Peptide YY

What is Peptide YY?

Peptide YY (PYY) is a 36-amino-acid peptide hormone co-secreted with GLP-1 by L-cells in the distal small intestine and colon in response to nutrient ingestion. It circulates primarily as two forms — the full-length PYY(1-36) and the truncated PYY(3-36), cleaved by the enzyme dipeptidyl peptidase-4 (DPP-4). PYY(3-36) is the biologically active satiety fragment, selective for the Y2 receptor, and is the form targeted by essentially all therapeutic development to date. Together with GLP-1, PYY is half of the gut's postprandial satiety signaling axis — the endogenous basis for why meals make you feel full.

What Peptide YY Is Investigated For

Peptide YY matters on two levels. As a piece of physiology, it is one of the best-characterized postprandial satiety hormones — the Batterham et al. 2002 Nature paper and its 2003 NEJM follow-up in obese subjects established PYY(3-36) as an endogenous Y2-receptor-driven brake on food intake, and the roughly tenfold postprandial surge seen after Roux-en-Y gastric bypass is widely regarded as one of the mechanistic reasons bariatric surgery produces sustained satiety in a way caloric restriction alone does not. As a drug, PYY(3-36) has repeatedly been harder to translate than the physiology suggested. The intranasal PYY(3-36) program (Nastech/MDRNA) failed Phase 2 for weight loss in the mid-2000s, and Novo Nordisk's long-acting PYY3-36 analogue NNC0165-1875 / PYY1875 reported only modest add-on benefit over semaglutide in Phase 2 and was tolerability-limited. The consistent pattern: nausea and vomiting dose-limit the satiety effect, and the therapeutic window is narrower than GLP-1 alone. The honest framing today is that PYY is the other half of the gut-hormone satiety story alongside GLP-1, that endogenous PYY physiology is important for understanding both obesity and bariatric surgery outcomes, and that a pharmaceutical PYY product for obesity has not yet crossed the efficacy-and-tolerability threshold to reach the market.

History & Discovery

Peptide YY was isolated in 1980 by Kazuhiko Tatemoto and Viktor Mutt at the Karolinska Institute in Stockholm. Working from porcine upper intestinal tissue, they used a then-novel chemical detection method that picked peptides out by their C-terminal amide rather than by bioassay, and reported two new intestinal hormones in the same Nature paper: PHI and PYY. Tatemoto published the complete 36-amino-acid sequence in PNAS in 1982, and the same chemical method applied to brain tissue yielded the family's third member, neuropeptide Y, later that year. The name 'peptide YY' referenced the tyrosine (Y) residues at both the C- and N-termini of the 36-amino-acid sequence. PYY was placed in the pancreatic polypeptide family and shown to inhibit pancreatic exocrine secretion and gastrointestinal motility — but its central role in satiety signaling would take another two decades to establish. The transformative paper came in August 2002, when Rachel Batterham and colleagues at Imperial College London published in Nature that peripheral infusion of PYY(3-36) at physiologic postprandial concentrations reduced ad libitum caloric intake by roughly 33% over 24 hours in healthy human volunteers. The paper linked PYY(3-36) to Y2-receptor-mediated inhibition of orexigenic NPY/AgRP neurons in the arcuate nucleus, establishing PYY as a genuine endogenous satiety hormone rather than a secondary motility regulator. A follow-up study in the New England Journal of Medicine in 2003 extended the finding to obese subjects, showing comparable ~30% suppression of caloric intake in both obese and lean individuals and — crucially — that obese subjects had lower endogenous postprandial PYY, suggesting that PYY deficiency might contribute to obesity pathogenesis. These results triggered a wave of therapeutic development, and the intranasal route then failed twice. Nastech Pharmaceutical (later MDRNA) developed an intranasal PYY(3-36) spray and licensed it to Merck in 2004. The trial published in 2007 was Merck's: 133 obese adults on placebo, 200 mcg or 600 mcg three times daily for 12 weeks, which missed its efficacy endpoint outright and in which 27 of 46 patients in the high-dose arm — 59% — discontinued because of nausea and vomiting, leaving only 12 to finish. Merck had already returned the rights by then. Nastech went on to run its own larger Phase 2, a 24-week dose-ranging study in 551 obese patients, and that one missed its weight-loss endpoint too. Novo Nordisk developed a long-acting PYY(3-36) analogue, NNC0165-1875 (PYY1875), designed for once-weekly dosing and intended primarily as an add-on to semaglutide; Phase 2 results reported in 2025 showed only modest incremental weight loss and tolerability limitations, and the program was subsequently discontinued. In parallel with the drug development story, observational and mechanistic work established that Roux-en-Y gastric bypass surgery produces roughly tenfold exaggerated postprandial PYY release, sustained for years — a finding now widely regarded as one of the central mechanisms underlying bariatric surgery's durable satiety and weight-loss effects. This has made PYY biology a consistent reference point in both the gut-hormone pharmacology literature and the bariatric-physiology literature, even though a PYY-based drug has yet to succeed commercially.

How It Works

After a meal, your intestines release PYY along with GLP-1. PYY then travels through the bloodstream to appetite centers in your brain, essentially telling them 'food has arrived, you can stop looking for more.' The larger the meal — especially protein and fat — the more PYY is released.

PYY is produced by enteroendocrine L-cells in the distal small intestine and colon and is co-secreted with GLP-1 in response to nutrient ingestion, with release proportional to caloric load and particularly driven by protein and long-chain fatty acids. The full-length PYY(1-36) is cleaved at the N-terminus by DPP-4 to yield PYY(3-36), the Y2-receptor-selective active fragment. PYY(3-36) crosses the blood-brain barrier and acts on Y2 autoreceptors on orexigenic NPY/AgRP neurons in the arcuate nucleus of the hypothalamus, suppressing their firing and thereby disinhibiting downstream anorexigenic POMC neurons. Additional sites of action include the vagus nerve, brainstem (area postrema, nucleus tractus solitarius), and reward-processing regions of the cortex and limbic system. Functional MRI studies in humans have shown that PYY(3-36) infusion modulates activity in hypothalamic, brainstem, and corticolimbic appetite circuits, with the pattern of activation shifting toward what is seen in the fed state. Peripheral effects include slowed gastric emptying and inhibition of pancreatic exocrine secretion, both of which reinforce the satiety signal. The half-life of endogenous PYY(3-36) is short (roughly 8-12 minutes), which is why therapeutic development has focused on longer-acting analogues or alternative delivery routes.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about Peptide YY:

• 01Why PYY(3-36) drug development has repeatedly failed the tolerability-efficacy test while GLP-1 agonism has succeeded — whether this reflects pharmacology (narrow therapeutic window at Y2) or molecule engineering (short half-life, delivery challenges) is not settled.
• 02Whether a next-generation long-acting PYY(3-36) analogue with better tolerability could add clinically meaningful benefit on top of GLP-1 or GLP-1/GIP agonists.
• 03The causal status of low endogenous PYY in obesity — whether blunted postprandial PYY is a driver of obesity or a consequence of altered meal patterns, gut flora, or adiposity itself. A 2026 Gastroenterology paper identified a distinct obesity subphenotype with reduced enteroendocrine GLP-1 and PYY synthesis that showed enhanced tirzepatide response — early evidence that low-incretin/PYY signaling defines a clinically actionable subgroup rather than just being a correlate of adiposity.
• 04Long-term cardiovascular, pancreatic, and bone effects of chronic PYY receptor agonism — not characterized because no drug has reached chronic licensed use.
• 05The relative contribution of PYY versus GLP-1 versus other gut-hormone changes to the satiety and weight-loss effects of bariatric surgery — observational correlations are strong but causal dissection is harder.
• 06Whether dietary strategies that maximize endogenous PYY release (high-protein meals, fiber, long-chain fatty acids) translate into meaningful long-term weight or appetite outcomes beyond the short-term satiety effect.
• 07The role of PYY in Y1 versus Y2 versus Y5 receptor signaling balance and whether selective Y2 agonists could separate satiety from adverse GI effects.

Forms & Administration

Native PYY(3-36) has a short plasma half-life (~8-12 minutes) and is not orally bioavailable. Clinical studies have used IV infusion (investigational only), subcutaneous injection, and intranasal spray (Nastech program, discontinued). No FDA-approved PYY product exists for any indication. Investigational long-acting analogues such as NNC0165-1875 (Novo Nordisk, discontinued after Phase 2) have used weekly SC dosing. Any peptide administered outside an approved indication should only be considered under qualified medical supervision, and compounded PYY does not offer the quality controls of sponsor-manufactured trial product.

Timeline of Effects

Common Questions

Who Peptide YY Is NOT For

Drug & Supplement Interactions

PYY(3-36) is a peptide cleared by DPP-4 and peptidase-mediated degradation, so classical CYP-based drug-drug interactions are not expected. Theoretical and mechanism-based interactions include the following. DPP-4 inhibitors (sitagliptin, linagliptin, saxagliptin) alter PYY processing, and the direction is the opposite of what intuition suggests. DPP-4 is the enzyme that creates active, Y2-selective PYY(3-36) by clipping two residues off PYY(1-36) — so inhibiting it shifts the balance toward the less selective full-length form rather than prolonging the active one. This has been tested directly in humans, in a small study infusing PYY(1-36) with and without sitagliptin alongside PYY(3-36) to characterise the conversion. The real-world significance in people taking DPP-4 inhibitors for type 2 diabetes is modest and not considered a safety concern. GLP-1 receptor agonists (semaglutide, tirzepatide, liraglutide) share overlapping pharmacology with PYY; co-administration has been formally studied in the Novo Nordisk NNC0165-1875 plus semaglutide Phase 2 program, where additive GI tolerability burden was observed. Drugs that slow gastric emptying (opioids, anticholinergics, amylin analogues) can compound PYY's gastric-emptying effect, potentially worsening nausea or delaying oral drug absorption. For medications with narrow absorption windows or time-sensitive pharmacokinetics (oral contraceptives, certain antibiotics, levothyroxine), slowed gastric emptying is a theoretical consideration though not well characterized for PYY specifically. Beyond these mechanism-based considerations, the pharmacokinetic drug-interaction profile of PYY(3-36) is limited by the absence of a marketed product on which to generate comprehensive data.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions