Appetite Regulation: Peptides, Hunger and Satiety Hormones

How appetite is regulated

Hunger and fullness are set by signals that travel to the brain from the gut and pancreas, and from fat tissue. Most of those signals are peptides. That's why this area has produced the most successful peptide drugs of the past decade. It's also why some research peptides sold for other goals change appetite as a side effect.

Hunger signals, ghrelin above all, have their own page on hunger hormone modulation. The signals that end a meal are covered under satiety enhancement. Compounds aimed at fat metabolism rather than appetite sit in the wider fat-loss and metabolic peptides hub.

The main hunger and satiety hormones

Small human experiments show the effect directly. In a 2001 crossover study, nine healthy volunteers ate 28% more from a buffet during an intravenous ghrelin infusion than during saline. A year later, a team from the same London hospital reported that infusing PYY(3-36) at normal after-meal levels cut food intake by 33% over 24 hours.

Leptin is the cautionary case. In a 1999 randomized trial of daily leptin injections, weight loss in adults with obesity rose with dose, but the top-dose group had only eight people at 24 weeks and lost about 7 kg on average. Most people with obesity already have high leptin levels. The drugs that worked target satiety instead.

Approved prescription medicines (as of October 2026)

Everything in this section is a prescription medicine approved at specific doses with a step-up schedule. The doses below are what trials and labels report. They aren't guidance.

Semaglutide is a GLP-1 receptor agonist. In the STEP 1 trial, adults with obesity on 2.4 mg weekly injections lost 14.9% of body weight at 68 weeks, compared with 2.4% on placebo. As of October 2026, the FDA has approved two newer forms for weight management:

• Wegovy pill (oral semaglutide 25 mg daily), approved December 22, 2025. In the 64-week OASIS 4 trial, average weight loss was 13.6% counting everyone randomized.
• Wegovy HD (7.2 mg weekly injection), approved March 19, 2026, for adults who have tolerated 2.4 mg for at least four weeks. In the 72-week STEP UP trial it produced 18.8% weight loss versus 15.5% on 2.4 mg. Novo Nordisk reports that altered skin sensation (dysesthesia) affected 22% on 7.2 mg versus 6% on 2.4 mg.

The semaglutide profile has the full label history.

Tirzepatide activates both GLP-1 and GIP receptors and is approved for weight management as Zepbound. In SURMOUNT-1, the top dose of 15 mg weekly produced 20.9% weight loss at 72 weeks, versus 3.1% on placebo. Gastrointestinal side effects clustered in the dose-escalation period. Researchers still debate how much the GIP component adds to appetite control itself.

Late-stage candidates: retatrutide and CagriSema

Retatrutide adds glucagon receptor activity to GLP-1 and GIP. As of October 2026 it has five positive Phase 3 trials and is not approved anywhere. Lilly says it plans to file with the FDA in the first quarter of 2027. In TRIUMPH-4 (adults with obesity and knee osteoarthritis), the 12 mg weekly dose produced 28.7% average weight loss at 68 weeks among participants who stayed on treatment. Participants started at 2 mg weekly and stepped up every four weeks to their target dose.

The appetite effect showed up in that trial's safety table. "Decreased appetite" was logged as an adverse event in about 18-19% of retatrutide participants versus 9.4% on placebo. Dysesthesia reached 20.9% at 12 mg. The retatrutide profile lists all five trials.

CagriSema pairs semaglutide 2.4 mg with cagrilintide 2.4 mg, a long-acting amylin analogue, in one weekly injection. In REDEFINE 1 it produced 20.4% weight loss at 68 weeks versus 3.0% on placebo. Gastrointestinal side effects affected 79.6% of participants. Novo Nordisk filed for FDA approval in December 2025 and expects a decision by late 2026; as of October 2026 it is not approved in the US or EU.

In the open-label REDEFINE 4 trial, CagriSema lost to tirzepatide 15 mg (23.0% versus 25.5% at 84 weeks) and missed its non-inferiority goal. Cagrilintide alone entered its own Phase 3 program, RENEW, in November 2025; the cagrilintide profile follows it.

Ghrelin mimetics push appetite the other way

Growth hormone secretagogues such as GHRP-6 and ipamorelin act on the ghrelin receptor. They're sold for research use to raise growth hormone, but because they mimic ghrelin, some also raise hunger.

GHRP-6 is the clearest example. In a 1995 rat study, GHRP-6 injected into the brain made already-fed rats start eating, in a dose-dependent way that didn't track growth hormone levels. Users report the same thing: a strong wave of hunger soon after an injection. Some lifters welcome that while bulking; people cutting usually avoid it. The GHRP-6 profile covers its other effects.

User communities and vendor copy both describe ipamorelin as causing much less hunger. The evidence is thinner than that reputation. Its 1998 development paper showed it was more selective than GHRP-6 for growth hormone release (it didn't raise ACTH or cortisol in pigs), but that study didn't measure appetite. A 2001 mouse study found that two weeks of either ipamorelin or GHRP-6 increased food intake and body fat by a route independent of growth hormone. We found no human study comparing hunger on the two, so the "much less hunger" claim rests on user reports.

AOD-9604 and fragment 176-191

AOD-9604, a modified version of growth hormone fragment 176-191, is often lumped in with appetite peptides. It was developed as an obesity drug and failed its human trials. In the largest (OPTIONS, about 500 adults with obesity taking oral doses of 0.25-1 mg daily for 24 weeks), weight loss wasn't significantly different from placebo. The developer then stopped work on it for obesity. FDA's 2024 review for its compounding advisory committee found no human data for injected AOD-9604 and noted that its molecular target has never been identified.

What users report

Community reports are self-selected and unverified, and many involve products of unknown quality.

• People on prescription GLP-1 drugs commonly describe less "food noise" (fewer intrusive thoughts about food) and feeling full sooner. That fits the reduced intake seen in trials, though "food noise" isn't a standard trial endpoint.
• Many people using gray-market retatrutide describe starting well below the trial's 2 mg weekly dose and splitting it across the week. No trial has tested those schedules.
• Some users who add cagrilintide to a GLP-1 describe very strong appetite loss, and a minority describe low mood or anxiety. We haven't seen that mood signal in trial reports.

Research-use vials aren't the prescription drugs

Semaglutide and tirzepatide are FDA-approved prescription medicines made under drug manufacturing controls. A vial labeled "retatrutide" and sold "for research use only" is a different product. Nobody has verified what's in it or whether it's sterile.

As of October 2026, the FDA says it has warned companies selling GLP-1 drugs falsely labeled "for research purposes" or "not for human consumption." It also states that retatrutide and cagrilintide can't be used in compounding under federal law. The trial results on this page come from the manufacturers' own products and say nothing reliable about a gray-market vial.

What we still don't know

• Whether the FDA approves CagriSema by late 2026, and whether Lilly's retatrutide filing goes ahead in early 2027.
• How much of the extra weight loss with tirzepatide and retatrutide comes from eating less rather than burning more. Retatrutide's glucagon component is thought to raise energy use, but trials don't separate the two.
• Whether ipamorelin really causes less hunger than GHRP-6 in people. The only direct comparison we found is in mice.
• Whether the mood changes some users describe with cagrilintide hold up in controlled data.