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Somapacitan

A once-weekly growth hormone analogue that hitches a ride on circulating albumin — the first long-acting GH approved in the United States for adults, now also approved in children for GH deficiency, small-for-gestational-age short stature, Noonan syndrome and idiopathic short stature.

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Last updated 29 citations
TL;DR

Somapacitan (Sogroya) is growth hormone modified to stick to albumin in the blood, so one injection lasts a week instead of a day. It grows children about as well as daily growth hormone and does the same things in adults with growth hormone deficiency, with a similar side effect profile. Its real advantage is 52 injections a year instead of 365.

What is Somapacitan?

Somapacitan is human growth hormone re-engineered so that it only has to be injected once a week instead of every day. The protein part is the familiar 191-amino-acid growth hormone sequence with a single amino acid swap — leucine to cysteine at position 101 — which creates an attachment point for a small chemical side-chain made of an albumin-binding group and a hydrophilic spacer. That side-chain lets the molecule bind reversibly to serum albumin, the most abundant protein in blood, which protects it from clearance and releases it gradually. The result is a 23.3 kDa molecule, produced in E. coli, that delivers a week of growth hormone exposure from one injection. Sold as Sogroya by Novo Nordisk, it was approved by FDA in August 2020 for adults with growth hormone deficiency — the first long-acting growth hormone approved in the US — and the paediatric label has since expanded to cover growth hormone deficiency, short stature in children born small for gestational age, Noonan syndrome and idiopathic short stature from age 2.5.

What Somapacitan Is Investigated For

Somapacitan's trial program is organized around a single question — can one weekly injection do what seven daily ones do — and across settings the answer has consistently been yes. In adults, the phase 3 REAL 1 trial randomized 301 treatment-naive patients with GH deficiency across 17 countries and used change in truncal fat percentage as its primary endpoint, a choice that reflects what GH replacement actually does for adults. Somapacitan beat placebo at 34 weeks (estimated difference -1.53%, 95% CI -2.68 to -0.38, P = 0.0090) and improved visceral fat, lean body mass and IGF-I, with benefits maintained to 86 weeks and a safety profile matching daily GH. In children, the phase 3 REAL4 trial randomized 200 treatment-naive children with GH deficiency 2:1 against daily Norditropin and confirmed non-inferiority at 52 weeks, with annualized height velocity of 11.2 versus 11.7 cm/year, comparable IGF-I standard deviation scores inside the normal range, and almost identical injection-site reaction rates (5.3% vs 5.9%). The three-year REAL4 data show sustained growth, with height SDS approaching mid-parental height in both the continuous and the switched groups. Phase 3 trials in children born small for gestational age, with Noonan syndrome, and with idiopathic short stature followed, supporting the expanded label, and a Turner syndrome phase 3 trial has been published without yet appearing in the US indications. The reason patients and clinicians care is simpler than any of this: REAL4 found a greater reduction in treatment burden with somapacitan, which is the entire point of a weekly injection in a therapy that runs for years.

Growth hormone replacement in adults with GH deficiency (FDA indication)
Strong90%
Growth failure in children with GH deficiency (FDA indication)
Strong90%
Short stature in children born small for gestational age without catch-up growth (FDA indication)
Strong90%
Growth failure associated with Noonan syndrome (FDA indication)
Moderate70%
Idiopathic short stature (FDA indication)
Moderate70%
Reducing treatment burden for patients switching from daily growth hormone
Strong90%
Short stature in Turner syndrome (phase 3 data published; not in the current US label)
Moderate70%

History & Discovery

Growth hormone replacement has had the same problem since recombinant somatropin replaced cadaver-derived pituitary extract in 1985: it works, and it requires an injection every day, for years, usually in a child. Adherence erodes predictably over long courses, and poor adherence costs height that cannot be recovered. The search for a long-acting growth hormone therefore ran for decades, and it produced a long list of failures — depot suspensions that released erratically, PEGylated molecules that accumulated in tissue, formulations that generated antibodies — before three different solutions arrived almost simultaneously in the late 2010s and early 2020s. Somapacitan, developed by Novo Nordisk as NN8640, took the albumin-binding route, borrowing a strategy the company had already proven in metabolic medicine: the same principle of attaching a fatty albumin-binding side-chain underlies liraglutide and semaglutide. Applied to growth hormone, it meant changing a single residue — leucine 101 to cysteine — to create a conjugation site, then attaching an albumin binder through a hydrophilic spacer. The GH protein itself was otherwise left alone, so receptor pharmacology was unchanged and only clearance was slowed. The clinical program was named REAL and ran in parallel across adults and children. REAL 1, a phase 3 trial in 301 treatment-naive adults with GH deficiency across 17 countries, used change in truncal fat percentage as its primary endpoint — a choice worth noticing, because it reflects that adult GH replacement is about body composition and metabolic function rather than growth. It met that endpoint against placebo and matched daily GH over 86 weeks. FDA approved Sogroya for adults with GH deficiency on 28 August 2020 under BLA 761156, the first long-acting growth hormone approved in the United States. Paediatric approval came later and required its own program. REAL 3, a phase 2 dose-finding trial, ran to four years. REAL4, the phase 3 trial, randomized 200 treatment-naive children at 86 sites in 20 countries against daily Norditropin and confirmed non-inferiority at 52 weeks, with three-year data published in 2025 showing both continuing and switched groups converging on mid-parental height. The label then expanded further on the strength of phase 3 trials in children born small for gestational age, in Noonan syndrome, and in idiopathic short stature, all reported in 2026 — an unusually rapid sequence of indication expansions. A phase 3 trial in Turner syndrome has been published without the indication yet appearing in the US label. Somapacitan entered a market it shares with two structurally unrelated solutions to the same problem — lonapegsomatropin, a cleavable PEG prodrug of unmodified somatropin, and somatrogon, a GH fused to hCG beta-subunit carboxy-terminal peptides. Network meta-analysis has not separated them, and the Growth Hormone Research Society issued an updated consensus statement on long-acting growth hormone in 2026 largely because clinical practice had to absorb three new products faster than guidance could be written.

How It Works

Growth hormone works well but disappears from the blood within hours, which is why normal treatment means an injection every single day for years. Somapacitan is growth hormone with a small chemical handle attached that grabs onto albumin, a protein already circulating in the blood in large amounts and designed to stay there. Holding onto albumin keeps the growth hormone from being cleared, and it is released slowly over the following week. The growth hormone itself works exactly as it always did — only how long it lasts has changed.

Somapacitan-beco is a human growth hormone analogue consisting of the 191-amino-acid hGH protein with a single L101C substitution, to which an albumin-binding side-chain is conjugated at position 101. The side-chain comprises a lipophilic albumin binder joined to the protein through a hydrophilic spacer, contributing 1,191.39 g/mol of the molecule's 23,305.10 g/mol total; the complete molecular formula is C1038H1609N273O319S9, and the protein is expressed in Escherichia coli. The albumin binder associates non-covalently and reversibly with circulating serum albumin, which has a half-life measured in weeks and is present at high concentration. Binding shields somapacitan from renal filtration and from GH receptor-mediated clearance, and the equilibrium between bound and free drug provides a slow, continuous release of active molecule. Because the growth hormone portion is otherwise unmodified, the free fraction engages the GH receptor conventionally, dimerizing it and activating JAK2/STAT5 signalling to induce hepatic and local IGF-1 production — the proximate driver of linear growth in children and of the body composition, lipid and bone effects of replacement in adults. This is one of three distinct engineering solutions to the same problem now in clinical use, and the differences matter for how each behaves. Somapacitan uses reversible albumin binding on a modified GH molecule. Lonapegsomatropin is a prodrug in which unmodified somatropin is released from a PEG carrier by a cleavable linker, so the circulating active species is native GH. Somatrogon is a fusion protein, GH joined to carboxy-terminal peptide sequences from the beta subunit of human chorionic gonadotropin. All three achieve weekly dosing; none has been shown superior to the others in head-to-head or network comparison. The pharmacodynamic consequence of weekly dosing is a weekly IGF-I profile rather than the steadier state produced by daily injection. IGF-I rises after each dose and falls across the interval, which makes the time of sampling relative to the last injection an essential part of interpreting a result — dedicated population modelling has been published for exactly this purpose. In the phase 3 trials, mean IGF-I SDS remained within the normal range of -2 to +2 and comparable to daily GH, and three-year data found bioactive IGF-I and the bioactive-to-total ratio similar between weekly and daily treatment.

Evidence Snapshot

Overall Confidence88%

Human Clinical Evidence

Extensive and recent. FDA-approved since August 2020 for adult GH deficiency on the basis of the 301-patient phase 3 REAL 1 trial across 17 countries, with paediatric approval resting on the 200-patient REAL4 trial at 86 sites in 20 countries and its three-year extension, four-year phase 2 data from REAL 3, and subsequent phase 3 trials in small-for-gestational-age, Noonan syndrome and idiopathic short stature populations. Supplemented by a Chinese phase 3 trial, a published Turner syndrome phase 3 trial, pooled analyses, and multiple network meta-analyses against the other long-acting agents.

Animal / Preclinical

Adequate and largely confirmatory. Growth hormone receptor pharmacology and the GH-IGF-1 axis are among the most thoroughly characterized endocrine systems; the preclinical work specific to somapacitan addressed the albumin-binding pharmacokinetics rather than the underlying biology, which was already established.

Mechanistic Rationale

Very strong. Growth hormone replacement in deficiency is foundational endocrinology, and the albumin-binding modification extends duration without altering receptor interaction — a pharmacokinetic intervention on a pharmacologically settled molecule.

Research Gaps & Open Questions

What the current literature has not yet settled about Somapacitan:

  • 01Final adult height on weekly dosing across a complete growth period. The longest datasets run three to four years; no cohort treated with somapacitan from diagnosis to epiphyseal closure has yet reported adult height.
  • 02Whether the weekly IGF-I excursion matters over a decade of treatment. Mean IGF-I SDS stays within the normal range and bioactive IGF-I is comparable to daily GH at three years, but a within-range mean conceals a peak and a trough that daily dosing does not produce.
  • 03How somapacitan compares with lonapegsomatropin and somatrogon. Three structurally unrelated long-acting growth hormones reached the market within a few years of each other, network meta-analysis has not separated them, and no head-to-head trial has been run.
  • 04Whether weekly dosing actually improves real-world adherence and therefore real-world outcomes. Trials measured treatment burden and found it reduced, but trial populations are not where adherence typically fails.
  • 05Long-term oncologic safety in children treated for non-deficiency indications such as idiopathic short stature, where the benefit is cosmetic rather than replacement of a missing hormone and the risk-benefit calculation is accordingly different.
  • 06Whether the Turner syndrome data will translate into an approved indication, and how somapacitan performs in the other conditions where daily growth hormone is established but weekly products have not been tested.

Forms & Administration

Subcutaneous injection once weekly, at any time of day, into the upper arms, thigh, abdomen or buttocks, with regular site rotation to avoid lipohypertrophy and lipoatrophy. Sogroya is supplied in single-patient-use prefilled pens with a deliverable volume of 1.5 mL, in multiple strengths — the 5 mg/1.5 mL pen contains 3.3 mg per mL and the 10 mg/1.5 mL pen 6.7 mg per mL — formulated with histidine, mannitol, phenol and poloxamer 188 at approximately pH 6.8. Paediatric dosing is weight-based: 0.16 mg/kg once weekly for GH deficiency in both treatment-naive children and those switching from daily somatropin, and 0.24 mg/kg once weekly for small-for-gestational-age short stature, Noonan syndrome and idiopathic short stature, with subsequent individualization based on growth response. Adult dosing is individualized and titrated against IGF-I, with specific considerations for patients over 65, those with hepatic impairment and women receiving oral oestrogen. Patients switching from daily growth hormone choose a preferred weekly day and stop the daily product the day before. Treatment should be supervised by a healthcare provider experienced in managing growth hormone deficiency and the relevant paediatric conditions.

Dosing & Protocols

The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.

Typical Range

Paediatric growth hormone deficiency: 0.16 mg/kg body weight once weekly, both for treatment-naive children and for those switching from daily somatropin. Small-for-gestational-age short stature, Noonan syndrome and idiopathic short stature: 0.24 mg/kg once weekly. Adult GH deficiency: individualized and titrated against IGF-I rather than weight-fixed, with lower starting doses and slower titration in patients over 65 and in women receiving oral oestrogen.

Frequency

Once weekly, on the same day each week, at any time of day.

Timing Considerations

Time of day

Any time of day — the albumin-bound reservoir makes timing irrelevant, unlike daily GH, which is conventionally given at bedtime

Relative to meals

No relationship to food

Relative to exercise

Not tied to exercise timing.

The same weekday each week. Clinics usually fix the IGF-I sampling day relative to the injection day so that serial results can be compared.

Cycle Length

Continuous. In children, treatment runs through the growth window until epiphyseal closure — the label contraindicates use for growth promotion once epiphyses are closed. In adults with GH deficiency, replacement is generally lifelong, with periodic reassessment of ongoing need.

Protocol Notes

The weekly schedule is the entire point of the drug, and the practical advice follows from it. Pick a day, keep it, and inject at whatever time of day suits — unlike daily GH, there is no attempt to mimic the nocturnal GH pulse, because the albumin-bound reservoir smooths exposure across the week regardless of when the dose is given. Patients switching from daily somatropin choose their preferred weekly day and stop the daily product the day before the first weekly dose. Injection sites — upper arms, thigh, abdomen, buttocks — should be rotated systematically. Both lipohypertrophy and lipoatrophy have been reported with growth hormone products, and a published case of reversible lipoatrophy in an adult on somapacitan is a reminder that rotation is not a formality. IGF-I monitoring is where weekly dosing genuinely changes practice. Because IGF-I rises after each dose and declines across the interval, a result is only interpretable alongside the time since the last injection, and population modelling has been published specifically to guide sampling and dose adjustment. Clinics typically standardize the sampling day relative to injection day so that serial results are comparable; titrating a dose on an IGF-I drawn at an unrecorded point in the week is a real way to get the dose wrong. Dosing in adults deserves separate mention because it is not weight-based in the way paediatric dosing is. Starting doses are lower and titration slower in patients over 65 and in those with hepatic impairment, and women taking oral oestrogen typically need higher doses because first-pass hepatic oestrogen blunts the IGF-I response to growth hormone — a transdermal oestrogen route avoids that effect, which is sometimes a reason to change the oestrogen rather than the GH. Children on growth hormone of any kind need periodic assessment for slipped capital femoral epiphysis and for scoliosis progression, and any new limp, hip or knee pain warrants prompt evaluation.

Somapacitan is approved for growth hormone deficiency in adults and for specific paediatric growth conditions, and should be prescribed and monitored by a clinician experienced in these diagnoses. It is not a wellness or anti-ageing product, and growth hormone use in adults without documented deficiency is neither approved nor supported by the evidence base described here.

Timeline of Effects

Onset

IGF-I responds within the first week and is the earliest measurable signal of adequate dosing. Clinical effects take longer and differ by population: in adults, improvements in body composition were measured at 34 weeks in REAL 1, with truncal fat the primary endpoint; in children, a meaningful change in height velocity needs at least three to six months of growth to measure reliably.

Peak Effect

In children, the first year of treatment produces the highest height velocity — 11.2 cm/year at 52 weeks in REAL4 — after which velocity settles to a lower but sustained rate, 7.4 to 7.8 cm/year between weeks 104 and 156 in the three-year data. This catch-up-then-plateau pattern is characteristic of growth hormone therapy rather than specific to somapacitan. In adults, body composition gains accrue over the first year and were maintained through 86 weeks.

After Discontinuation

Effects reverse. In children, growth velocity returns toward the untreated baseline and any height not gained before epiphyseal closure is permanently lost. In adults, the body composition and metabolic benefits of replacement regress over months as IGF-I returns to the deficient baseline, and the symptoms of adult GH deficiency — altered body composition, reduced exercise capacity, impaired quality of life — typically return. Because somapacitan is cleared from the albumin reservoir rather than stored in a depot, the washout is a matter of weeks rather than months.

Monitoring & Measurement

Bloodwork & Labs

  • •Serum IGF-I and IGF-I SDS — the central dose-titration marker, drawn at a standardized point relative to the weekly injection so that serial results are comparable
  • •Fasting glucose and HbA1c, given growth hormone's effect on insulin sensitivity
  • •Free T4 and TSH, because GH replacement can reveal central hypothyroidism
  • •Morning cortisol or dynamic adrenal testing in hypopituitary patients, since GH can unmask hypoadrenalism by reducing cortisone-to-cortisol conversion
  • •Lipid panel in adults, where dyslipidaemia is part of the adult GH deficiency phenotype

Functional & Performance Tests

  • •Accurate stadiometer height and height velocity in children, calculated over intervals of at least six months — the primary efficacy measure
  • •Bone age radiography annually in children, to track skeletal maturation and remaining growth potential
  • •DXA body composition in adults, which is what the adult trial endpoint actually measured and the most direct readout of replacement adequacy
  • •Fundoscopic examination if headache or visual change develops, given reports of intracranial hypertension with growth hormone
  • •Hip and spine examination in growing children, for slipped capital femoral epiphysis and scoliosis progression
  • •Sleep assessment where upper airway symptoms develop, particularly in children with predisposing conditions

When to Test

Baseline IGF-I, glucose, thyroid function, adrenal status and (in children) bone age before starting. IGF-I at roughly 6 to 12 weeks after initiation or any dose change, then at intervals once stable, always at a consistent point in the weekly cycle. Height every three to six months in children with velocity calculated over at least six months; bone age annually. Metabolic and thyroid panels at least annually. DXA in adults at baseline and periodically.

Interpretation & Notes

The discipline that distinguishes weekly from daily growth hormone is sampling timing. IGF-I varies predictably across the week on somapacitan, so a value drawn two days after an injection and one drawn six days after are not comparable, and titrating on an undated sample is a genuine way to end up over- or under-dosed. Fixing the sampling day relative to the injection day is the simple fix, and population modelling exists to support interpretation when that is not possible. The second thing worth attention is the rest of the pituitary: most adults on somapacitan have hypopituitarism rather than isolated GH deficiency, and starting GH can shift cortisol and thyroid hormone handling enough to require adjusting replacement of both — this is a common cause of someone feeling worse rather than better after starting treatment, and it is correctable. In children, the single most informative number remains height velocity over a six-month interval; shorter intervals are dominated by measurement error. All of this is specialist endocrinology monitoring rather than anything a patient manages alone.

Common Questions

How does somapacitan last a week when growth hormone lasts hours?

Through a borrowed carrier. A single amino acid in the growth hormone sequence is changed — leucine to cysteine at position 101 — and a small side-chain is attached there consisting of an albumin-binding group and a hydrophilic spacer. That side-chain binds reversibly to serum albumin, which circulates at high concentration and has a half-life of weeks. While bound, somapacitan is shielded from renal filtration and receptor-mediated clearance; it releases gradually, giving sustained exposure from one dose. Importantly the growth hormone portion itself is essentially unmodified, so it acts at the normal GH receptor in the normal way — the engineering changed the pharmacokinetics, not the pharmacology. Other long-acting growth hormones solve the same problem differently: lonapegsomatropin uses a cleavable PEG prodrug linker that releases unmodified somatropin, and somatrogon fuses GH to peptide sequences from the beta subunit of hCG.

Is weekly somapacitan as effective as daily growth hormone?

In the trials, yes. REAL4 randomized 200 treatment-naive children with GH deficiency to weekly somapacitan at 0.16 mg/kg or daily Norditropin at 0.034 mg/kg and confirmed non-inferiority at 52 weeks, with annualized height velocity of 11.2 versus 11.7 cm/year and comparable changes in height SDS, bone age and IGF-I SDS. At three years, height velocity between weeks 104 and 156 was 7.4 cm/year in children on somapacitan throughout and 7.8 cm/year in those switched from daily GH, with both groups approaching their mean mid-parental height SDS. In adults, REAL 1 demonstrated superiority over placebo on truncal fat and showed treatment effects consistent with daily GH over 86 weeks. Network meta-analyses comparing somapacitan with somatrogon and lonapegsomatropin have not established a clear winner among the long-acting agents.

Does a weekly injection mean weekly peaks and troughs in IGF-1?

It means a defined weekly IGF-I profile rather than a flat one, and this is a genuine difference from daily dosing that clinicians manage deliberately. IGF-I rises after the weekly dose and declines across the interval, so the timing of a blood draw relative to the last injection changes the number you get — model-based analyses have been published specifically to guide when to sample and how to interpret the result. In REAL4 and its extensions, mean IGF-I SDS stayed within the normal range of -2 to +2 and was similar to daily GH, and the three-year data also found bioactive IGF-I and the bioactive-to-total IGF-I ratio comparable between groups. The practical rule is that an IGF-I result is only interpretable if the time since the last dose is recorded.

Who should not take somapacitan?

The contraindications are those of growth hormone as a class, and several are absolute. Somapacitan must not be used in acute critical illness following open-heart surgery, abdominal surgery or multiple accidental trauma, or in acute respiratory failure, because pharmacologic GH in that setting increases mortality. It is contraindicated in active malignancy, in active proliferative or severe non-proliferative diabetic retinopathy, in children with closed epiphyses when used for growth promotion, and in children with Prader-Willi syndrome who are severely obese, have a history of upper airway obstruction or sleep apnoea, or have severe respiratory impairment, because of reports of sudden death. Hypersensitivity to somapacitan or its excipients is also a contraindication, and systemic hypersensitivity reactions have been reported post-marketing with somatropin.

Is somapacitan banned in sport?

Yes, explicitly and by name. WADA's class S2.2.3 covers 'Growth hormone (GH), its analogues and fragments' and names somapacitan directly alongside lonapegsomatropin and somatrogon. The prohibition is at all times, in and out of competition, for athletes of both sexes, and S2 substances are non-Specified. Being named on the List rather than merely covered by a category removes any ambiguity: somapacitan is a growth hormone analogue, it is prohibited, and an athlete with a genuine indication such as adult GH deficiency would need a Therapeutic Use Exemption. The same section separately names growth hormone fragments such as AOD-9604 and hGH 176-191, and GH-releasing factors and secretagogues are covered in S2.2.4.

Who Somapacitan Is NOT For

Contraindications
  • •Acute critical illness following open-heart surgery, abdominal surgery or multiple accidental trauma, and acute respiratory failure — pharmacologic growth hormone in this setting increases mortality.
  • •Active malignancy. Growth hormone and IGF-I are growth-promoting, and patients with a history of malignancy require clearance and ongoing surveillance before and during treatment.
  • •Active proliferative or severe non-proliferative diabetic retinopathy.
  • •Children with closed epiphyses, when somapacitan is being used for longitudinal growth promotion.
  • •Children with Prader-Willi syndrome who are severely obese, have a history of upper airway obstruction or sleep apnoea, or have severe respiratory impairment, because of reports of sudden death with growth hormone in this group.
  • •Known hypersensitivity to somapacitan-beco or to any excipient; systemic hypersensitivity reactions have been reported post-marketing with somatropin.
  • •Caution rather than contraindication in patients with diabetes or glucose intolerance, untreated hypoadrenalism, or untreated central hypothyroidism, all of which should be addressed before or alongside growth hormone replacement.

Drug & Supplement Interactions

Growth hormone interacts with several hormone systems in ways that matter clinically. The most important is with glucocorticoids: GH inhibits 11-beta-hydroxysteroid dehydrogenase type 1, reducing the conversion of cortisone to active cortisol, which can unmask previously undiagnosed central hypoadrenalism or require an increase in glucocorticoid replacement in patients already treated for it — a frequent and important consideration in hypopituitary adults, who often have multiple deficiencies. Conversely, supraphysiologic glucocorticoid therapy blunts the growth response in children. Growth hormone replacement can also reveal central hypothyroidism by altering peripheral thyroid hormone conversion, so thyroid function is checked before and during treatment and levothyroxine doses sometimes need adjustment. Oral oestrogen reduces the IGF-I response to growth hormone through a first-pass hepatic effect, so women on oral oestrogen typically need higher somapacitan doses; transdermal oestrogen does not have this effect, and switching route is sometimes the better adjustment. Because GH reduces insulin sensitivity, patients with diabetes may need higher doses of insulin or oral agents, and glucose should be monitored — though a dedicated analysis of weekly somapacitan found no adverse effect on glucose metabolism in adults with GH deficiency. Growth hormone can alter cytochrome P450-mediated clearance of some drugs, and caution is advised with agents metabolized by CYP3A4, including sex steroids, corticosteroids, ciclosporin and anticonvulsants. Combining somapacitan with another growth hormone product serves no purpose and risks over-replacement.

Safety Profile

Safety Information

Common Side Effects

HeadacheInjection-site reactions — low in the trials, reported by 5.3% on somapacitan versus 5.9% on daily GH in REAL4Arthralgia and musculoskeletal pain, particularly in adults starting replacementPeripheral oedema, more common in adults than childrenFatigueNasopharyngitisNausea

Cautions

  • • Contraindicated in acute critical illness after open-heart surgery, abdominal surgery or multiple accidental trauma, and in acute respiratory failure, because of increased mortality with pharmacologic GH doses in that setting
  • • Contraindicated in active malignancy; GH and IGF-I are growth-promoting and patients with a history of malignancy need surveillance before and during treatment
  • • Contraindicated in active proliferative or severe non-proliferative diabetic retinopathy
  • • Contraindicated in children with closed epiphyses when used for longitudinal growth promotion
  • • Contraindicated in children with Prader-Willi syndrome who are severely obese, have a history of upper airway obstruction or sleep apnoea, or have severe respiratory impairment, because of reports of sudden death
  • • Glucose intolerance and new-onset type 2 diabetes can occur with GH therapy; a dedicated analysis found no adverse effect of weekly somapacitan on glucose metabolism in adults with GHD, but monitoring remains standard
  • • Intracranial hypertension, usually reversible on dose reduction or discontinuation, has been reported with growth hormone
  • • Hypoadrenalism can be unmasked, and central hypothyroidism revealed, as GH replacement alters cortisol and thyroid hormone handling
  • • Slipped capital femoral epiphysis and progression of scoliosis can occur during rapid growth in children
  • • Lipoatrophy at injection sites has been reported, including a published case of reversible lipoatrophy in an adult on somapacitan, which is why site rotation matters

What We Don't Know

The core indications rest on an unusually complete phase 3 program — REAL 1 in adults, REAL4 in paediatric GH deficiency with three-year follow-up, REAL 3 with four-year phase 2 data, REAL 5 and phase 3 trials in small-for-gestational-age, Noonan syndrome and idiopathic short stature, plus a Chinese phase 3 and a published Turner syndrome trial. What is not yet established is longer-horizon outcome data: final adult height on weekly dosing across the full growth period, whether the weekly IGF-I excursion has any consequence over a decade of treatment that the within-range mean conceals, and comparative long-term safety and efficacy against the other long-acting agents, which network meta-analysis has so far been unable to separate. A 2026 Growth Hormone Research Society consensus statement on long-acting growth hormone reflects how recently this class has had to be assimilated into practice.

Myths & Misconceptions

Myth

Somapacitan is just growth hormone with PEG attached.

Reality

That describes lonapegsomatropin, not somapacitan. Somapacitan carries a single L101C substitution with an albumin-binding side-chain attached at that position; it persists by binding reversibly to circulating serum albumin, the same strategy used in liraglutide and semaglutide. Lonapegsomatropin is a PEG prodrug that releases unmodified somatropin through a cleavable linker, and somatrogon is a fusion with hCG beta-subunit peptides. Three different engineering answers to the same problem.

Myth

A weekly injection must be less effective than daily growth hormone.

Reality

REAL4 confirmed non-inferiority in 200 treatment-naive children, with height velocity of 11.2 cm/year on weekly somapacitan versus 11.7 on daily Norditropin at 52 weeks, and three-year data showing both the continuous and the switched groups approaching mid-parental height. In adults, REAL 1 met its primary endpoint against placebo and matched daily GH through 86 weeks. The albumin reservoir maintains exposure between doses rather than letting it lapse.

Myth

Long-acting growth hormone means you can stop monitoring IGF-1.

Reality

It means you have to monitor it more carefully, not less. IGF-I rises after each weekly dose and falls across the interval, so the result depends on when the sample was drawn relative to the injection — population modelling has been published specifically to guide sampling and interpretation. Clinics generally fix the sampling day relative to injection day so that serial results are comparable.

Myth

Growth hormone like somapacitan is available for anti-ageing or body composition in healthy adults.

Reality

It is approved for documented growth hormone deficiency, and in the United States distributing human growth hormone for any use not authorized by FDA is a federal offence under 21 U.S.C. 333(e). The adult trial endpoint was truncal fat in patients with diagnosed GH deficiency — replacing a missing hormone, not supplementing a normal one. Somapacitan is also named explicitly on the WADA Prohibited List.

Myth

Because it lasts a week, missing a dose does not matter much.

Reality

The weekly schedule exists to improve adherence, not to make it optional. Exposure is maintained by continuous equilibrium between albumin-bound and free drug, and that reservoir empties over the week rather than carrying a reserve into the next one. Doses should be taken on the same day each week, and missed-dose handling should follow the prescribing information and the clinic's advice rather than improvisation.

Published Research

29 studies

Treatment of growth hormone deficiency with long-acting growth hormones in children, adolescents and adults: Clinical evidence and practical considerations

ReviewPMID: 42727727

Long-acting growth hormone: an updated Growth Hormone Research Society consensus statement

The 2026 Growth Hormone Research Society consensus on long-acting growth hormone — the field's attempt to standardize how this class is dosed, monitored and switched to, written because weekly products arrived faster than the practice guidance for them. The best single orientation to how somapacitan sits alongside daily GH and its weekly competitors.

Consensus StatementPMID: 42676236

Once-weekly somapacitan enhances linear growth in girls with Turner syndrome: a randomized controlled phase 3 study

A 2026 phase 3 trial in girls with Turner syndrome — a population in which growth hormone is long-established but somapacitan is not yet in the US label. Worth knowing as a reader because it illustrates the gap between what a long-acting GH has been shown to do and what it is currently approved to do.

Randomized Controlled TrialPMID: 42538806

Efficacy and Safety of Somapacitan versus Daily Growth Hormone in Children with Growth Hormone Deficiency: A Pooled Analysis of Randomised Trial Data

Meta-AnalysisPMID: 42348474

Once-weekly somapacitan vs. daily norditropin in GHD: a systematic review and meta-analysis of efficacy and safety in children and adults

Meta-AnalysisPMID: 42081070

Metabolic and muscular effects of switching from somatropin to somapacitan in adults with growth hormone deficiency

Observational StudyPMID: 41955533

Somapacitan in children born small for gestational age: a randomized controlled phase 3 trial

Randomized Controlled TrialPMID: 41782416

Once-weekly somapacitan in children with Noonan syndrome: randomized controlled phase 3 trial

Randomized Controlled TrialPMID: 41774755

Somapacitan in children with idiopathic short stature: a randomized controlled phase 3 study

Randomized Controlled TrialPMID: 41712606

Somapacitan in children born small for gestational age: 4-year results from phase 2

Clinical TrialPMID: 41614610

Safety and efficacy of somapacitan in adults with growth hormone deficiency who were switched from daily growth hormone therapy: A systematic review and meta-analysis

Meta-AnalysisPMID: 41259829

A pharmacological profile of somapacitan for the treatment of growth hormone deficiency

ReviewPMID: 41173798

Efficacy, safety, and insulin-like growth factor I of weekly somapacitan in children with growth hormone deficiency: 3-year results from REAL4

Three-year REAL4 data in 188 of the original 200 children. Height velocity between weeks 104 and 156 was 7.4 cm/year on continuous somapacitan and 7.8 cm/year after switching from daily GH, with height SDS of -0.95 and -1.08 against a mean mid-parental height SDS of -0.74 — both groups converging on their genetic target. Total and bioactive IGF-I and the bioactive-to-total ratio were similar between groups and within the normal range.

Randomized Controlled TrialPMID: 40400262

Somapacitan Is Effective and Well Tolerated in Chinese Children with Growth Hormone Deficiency: A Randomized Controlled Phase 3 Study

Randomized Controlled TrialPMID: 40324364

Efficacy of Somapacitan in Treatment-Fatigue Adult Patients With Growth Hormone Deficiency Previously Treated With Once-Daily Growth Hormone Injections

Randomized Controlled TrialPMID: 40107502

Growth Response to Weekly Somapacitan Therapy in Children With GH Deficiency Is Related to GH Thresholds in GH Stimulation Testing

Clinical TrialPMID: 40104568

Somapacitan in Children Born SGA: 52-Week Efficacy, Safety, and IGF-I Response Results From the Phase 2 REAL5 Study

Clinical TrialPMID: 39271158

Efficacy and Safety of Somapacitan Relative to Somatrogon and Lonapegsomatropin in Pediatric Growth Hormone Deficiency: Systematic Literature Review and Network Meta-Analysis

The indirect comparison of the three long-acting growth hormones now on the market, each solving the duration problem by a different mechanism — albumin binding for somapacitan, a cleavable PEG prodrug for lonapegsomatropin, and a CTP fusion for somatrogon. No clear winner emerges, which is the honest current state of the question in the absence of head-to-head trials.

Meta-AnalysisPMID: 39261416

Somapacitan-induced reversible lipoatrophy in an adult woman with hypopituitarism

Case ReportPMID: 39120809

Utilizing Somapacitan, a Long-acting Growth Hormone Formulation, for the Treatment of Adult Growth Hormone Deficiency: A Guide for Clinicians

ReviewPMID: 38992799

Developments in the Management of Growth Hormone Deficiency: Clinical Utility of Somapacitan

ReviewPMID: 38333899

Model-Based Analysis of IGF-I Response, Dosing, and Monitoring for Once-Weekly Somapacitan in Children With GH Deficiency

The population modelling work that tells clinicians when to draw IGF-I on a weekly regimen and how to interpret the result. It addresses the practical problem created by weekly rather than daily dosing — that IGF-I varies predictably across the dosing interval, so a result is uninterpretable without knowing how long ago the last injection was given.

Pharmacokinetic StudyPMID: 37818403

Effective GH Replacement With Somapacitan in Children With GHD: REAL4 2-year Results and After Switch From Daily GH

Randomized Controlled TrialPMID: 37406251

Weekly Somapacitan in GH Deficiency: 4-Year Efficacy, Safety, and Treatment/Disease Burden Results From REAL 3

The four-year extension of the phase 2 REAL 3 trial at 29 sites in 11 countries, following 50 prepubertal GH-naive children through three years at the 0.16 mg/kg weekly dose and one year after switching from daily GH. The longest continuous somapacitan exposure dataset in children, and the source of the disease- and treatment-burden measures that underpin the weekly-dosing rationale.

Clinical TrialPMID: 36995872

Guidance for the treatment of adult growth hormone deficiency with somapacitan, a long-acting growth hormone preparation

ReviewPMID: 36619571

Weekly somapacitan had no adverse effects on glucose metabolism in adults with growth hormone deficiency

A dedicated analysis of the metabolic question that attaches to every growth hormone product — whether weekly dosing worsens glucose handling in adults with GH deficiency. It did not, which matters because glucose intolerance is a recognized class effect and the weekly exposure profile differs from daily dosing.

Clinical TrialPMID: 36380045

Weekly Somapacitan is Effective and Well Tolerated in Children With GH Deficiency: The Randomized Phase 3 REAL4 Trial

REAL4 (Miller 2022), 200 treatment-naive children with GH deficiency at 86 sites in 20 countries, randomized 2:1 to weekly somapacitan 0.16 mg/kg or daily Norditropin 0.034 mg/kg. Non-inferiority was confirmed at 52 weeks with annualized height velocity of 11.2 versus 11.7 cm/year, comparable height SDS, bone age and IGF-I SDS, nearly identical injection-site reaction rates (5.3% vs 5.9%), and a greater reduction in treatment burden on weekly dosing.

Randomized Controlled TrialPMID: 36062966

Once-weekly Somapacitan is Effective and Well Tolerated in Adults with GH Deficiency: A Randomized Phase 3 Trial

REAL 1 (Johannsson 2020), the pivotal adult trial behind the August 2020 approval: 301 treatment-naive patients with adult GH deficiency across 17 countries, randomized 2:2:1 to weekly somapacitan, daily GH or weekly placebo. The primary endpoint, change in truncal fat percentage at 34 weeks, favoured somapacitan over placebo (estimated difference -1.53%, 95% CI -2.68 to -0.38, P = 0.0090), with visceral fat, lean body mass and IGF-I also improved and benefits maintained to 86 weeks.

Randomized Controlled TrialPMID: 32022863

Once-Weekly Somapacitan vs Daily GH in Children With GH Deficiency: Results From a Randomized Phase 2 Trial

Randomized Controlled TrialPMID: 31917835

Quick Facts

Class
Growth Hormone Analog (Albumin-Binding)
Tier
B
Evidence
Strong
Safety
Well-Studied
Updated
Oct 2026
Citations
29PubMed

Also known as

SogroyaSomapacitan-becoNN8640Long-Acting Growth Hormone

Tags

FDA-ApprovedGrowth HormoneHormoneInjectable

Related Goals

Body Composition

Evidence Score

Overall Confidence88%

Clinical Trials

View Clinical Trials

Links to ClinicalTrials.gov for reference. Listing does not imply endorsement.