Peptides for weight loss: what the trials and studies show

A peptide is a short chain of amino acids. Many of the body’s appetite and metabolism signals are peptides, including the gut hormones GLP-1 and GIP and the pancreatic hormone amylin. When people search for peptides for weight loss, they usually mean one of three quite different groups of products, and the evidence behind each group is very different.

The first group is licensed medicines. Semaglutide, sold as Wegovy for weight management, and tirzepatide, sold as Mounjaro and in the US also as Zepbound, are modified versions of gut hormones. They were approved after randomised trials in thousands of people, are made under pharmaceutical standards and are prescription-only in the UK and the US ^{[34] [32] [33]}. Our GLP-1 brand names guide explains which brand contains which drug.

The second group is drugs still in development. Retatrutide and cagrilintide have been tested in large trials run by Eli Lilly and Novo Nordisk, but neither is an approved medicine ^{[9] [15] [35]}. Products sold online under these names are not the trial drugs.

The third group is research-labelled vials and capsules sold for weight or fat loss with little or no human evidence: tesamorelin (a licensed drug for a narrow HIV use, also sold as a research product), AOD-9604, MOTS-c, and two compounds that are not peptides at all, 5-amino-1MQ and SLU-PP-332. These are sold by the same stores, which is why PepFinder tracks them together, but a research label means no regulator has assessed the product’s content, purity or safety. Our guide to what research peptides are covers what that label does and does not mean.

So there is no single peptide for weight loss that covers all of these. The sections below take each compound in turn, say what kind of study the evidence comes from (a randomised trial in people, a mouse study or a cell experiment), and then compare them.

Semaglutide is a long-acting analogue of GLP-1. Its developers changed two amino acids and attached a fatty-acid chain so that it binds to albumin in the blood and lasts about a week, allowing once-weekly injection ^[1]. It acts on the GLP-1 receptor to reduce appetite and slow stomach emptying.

The pivotal obesity trial, STEP 1, randomised 1,961 adults without diabetes to semaglutide 2.4 mg or placebo once weekly for 68 weeks, alongside lifestyle advice. Average weight fell by 14.9% on semaglutide against 2.4% on placebo ^[2]. In SELECT, 17,604 adults with cardiovascular disease and overweight or obesity but without diabetes had fewer major cardiovascular events on semaglutide 2.4 mg than on placebo (6.5% against 8.0%) ^[8].

Semaglutide is also made as a tablet. In OASIS 4, 307 adults with overweight or obesity took oral semaglutide 25 mg daily or placebo; average weight change at 64 weeks was −13.6% against −2.2% ^[5]. The evidence here is human randomised trials, the strongest kind, and it sits behind licensed products.

Tirzepatide is a single peptide that activates two receptors, GIP and GLP-1 ^[33]. In SURMOUNT-1, 2,539 adults without diabetes took tirzepatide 5 mg, 10 mg or 15 mg or placebo once weekly for 72 weeks. Average weight fell by 15.0%, 19.5% and 20.9% on the three doses, against 3.1% on placebo ^[3].

It is the only drug on this page that has been compared head to head with another for obesity. In SURMOUNT-5, 751 adults with obesity but without diabetes took the maximum tolerated dose of tirzepatide or semaglutide for 72 weeks. Average weight loss was 20.2% with tirzepatide and 13.7% with semaglutide; the trial was open-label and funded by Eli Lilly, which makes tirzepatide ^[4]. The detail is in our tirzepatide vs semaglutide comparison.

Retatrutide, also from Eli Lilly, adds a third receptor to tirzepatide’s two: glucagon. In obese mice, the glucagon activity raised energy expenditure on top of the reduced food intake from GIP and GLP-1 activity ^[11]. Online, it is sometimes called GLP-3, but there is no hormone of that name.

Its main peer-reviewed obesity trial is a phase 2 study of 338 adults. At 48 weeks, average weight loss was 8.7% on 1 mg, 17.1% on 4 mg, 22.8% on 8 mg and 24.2% on 12 mg once weekly, against 2.1% on placebo ^[9]. In the phase 3 TRIUMPH-1 trial of 2,339 adults, Lilly reported average weight loss of up to 28.3% at 80 weeks on 12 mg for people who stayed on treatment, or 25.0% counting everyone randomised ^[10]. We could not find TRIUMPH-1 in a peer-reviewed journal as of September 2026, so those are company figures.

A 2026 network meta-analysis of 58 randomised trials estimated weight loss 22.10 percentage points greater than placebo for retatrutide and 19.28 points for tirzepatide, while noting limited head-to-head evidence and overlapping confidence intervals ^[13]. The direct comparison, TRIUMPH-5, has not reported. Our retatrutide vs tirzepatide comparison covers both drugs in more depth.

Cagrilintide is a long-acting analogue of amylin, a hormone the pancreas releases with insulin after meals that promotes fullness. It is not a GLP-1 drug. On its own, in a 26-week phase 2 trial of 706 adults with obesity or overweight, weekly doses from 0.3 mg to 4.5 mg reduced body weight by 6.0% to 10.8%, against 3.0% on placebo; the top dose did better than daily liraglutide 3.0 mg (10.8% against 9.0%) ^[14].

Most of the larger trials test cagrilintide together with semaglutide, a combination Novo Nordisk calls CagriSema. In REDEFINE 1, 3,417 adults without diabetes took cagrilintide 2.4 mg with semaglutide 2.4 mg, or placebo, weekly for 68 weeks; average weight fell by 20.4% against 3.0% ^[15]. In REDEFINE 5, in Japan and Taiwan, CagriSema produced 18.4% weight loss against 11.9% with semaglutide alone, which shows what adding cagrilintide contributed in that trial ^[16].

Novo Nordisk has reportedly filed CagriSema with the FDA ^[17]. As of September 2026 we found no approval of cagrilintide or CagriSema, and the FDA states that cagrilintide is not a component of any approved drug ^[35].

Tesamorelin is a modified growth hormone-releasing hormone. It makes the pituitary release more growth hormone, and growth hormone breaks down visceral fat, the fat around the organs. It is licensed in the US as Egrifta for one narrow use: reducing excess abdominal fat in adults with HIV-associated lipodystrophy ^[19].

In the first phase 3 trial, 412 people with HIV took tesamorelin 2 mg or placebo daily for 26 weeks. Visceral fat measured by CT scan fell by 15.2% with tesamorelin and rose by 5.0% with placebo ^[18]. The fat came back after treatment stopped ^[20]. The US label says tesamorelin is not indicated for weight loss because its effect on body weight is neutral ^[19].

That makes tesamorelin a special case among peptides for fat loss. The trials show less visceral fat in a specific group of patients, not lower weight in people without HIV. No trial has tested it for weight loss in the general population, and the European marketing application was withdrawn in 2012 after the regulator’s committee doubted that the fat reduction translated into meaningful health benefits ^[40].

AOD-9604 is a 16-amino-acid fragment of human growth hormone, developed in Australia in the late 1990s as an oral anti-obesity drug. In obese mice, daily treatment for 14 days reduced body weight and fat and increased fat breakdown ^[22].

In people it did not work. The company ran six randomised trials, and the largest, a phase 2b trial that enrolled 536 adults with obesity, gave oral AOD-9604 0.25 mg, 0.5 mg or 1 mg daily or placebo for 24 weeks. It found no significant difference in weight loss at 12 weeks, its primary end point, and in February 2007 the company ended development for obesity. Reviewing the evidence in 2024, the FDA concluded there is a lack of evidence that AOD-9604 is effective for obesity by any route, and noted that no study of injection under the skin, the way it is now usually sold, has been published ^[21].

MOTS-c is a 16-amino-acid peptide encoded in mitochondrial DNA, first described in 2015. In that study, mice given 5 mg/kg a day by injection into the abdominal cavity were protected against diet-induced obesity and insulin resistance, and the peptide activated AMPK, an enzyme that senses cellular energy ^[23]. In female mice whose ovaries had been removed, a model of menopause, MOTS-c prevented the expected weight gain ^[24].

The human data so far are observational: in 10 sedentary young men, MOTS-c levels in muscle rose about 11.9-fold after cycling ^[38]. That shows the body makes more MOTS-c during exercise, not that injecting it helps weight. The first placebo-controlled trial of MOTS-c itself began in 2026 in an estimated 120 adults with prediabetes and overweight or obesity, with a 12-week primary outcome of insulin sensitivity; it had not reported when we checked ^[25].

Neither 5-amino-1MQ nor SLU-PP-332 is a peptide. Both are small synthetic molecules with no amino acids, sold by peptide stores and often searched for as peptides.

5-amino-1MQ blocks an enzyme called NNMT. In obese mice given it by injection three times a day for 11 days, the main abdominal fat pad was about 35% lighter than in untreated obese mice, with no significant change in food intake ^[26]. In a 28-day study, obese mice that stayed on a high-fat diet gained less fat on the higher dose (1.3 g against 4.7 g in controls), so the compound limited further gain rather than causing weight loss ^[27]. No human trial has been registered ^[28].

SLU-PP-332 activates the estrogen-related receptors, which control energy genes in muscle and heart. In obese mice given 50 mg/kg by injection twice a day for 28 days, energy expenditure rose and the mice ended about 12% lighter than untreated obese mice, without a change in food intake ^[29]. Its developers have since written that SLU-PP-332 lacks oral bioavailability, which is why they made a different compound for oral use ^[30]. No human trial has been registered ^[31].

For both compounds, every result comes from mice, rats or cells. Mouse obesity models respond to many compounds that later fail in people.

Asking which are the best peptides for weight loss is really asking how strong the evidence is for each one, and the answer falls into clear tiers. PepFinder does not rank them for personal use; this is a ranking of evidence only.

Tier 1, licensed medicines with large phase 3 trials: semaglutide and tirzepatide. Both have placebo-controlled trials in thousands of people, a head-to-head obesity trial ^[4], long-term safety monitoring and approved labels ^{[32] [33]}.

Tier 2, investigational drugs with large randomised trials: retatrutide and cagrilintide (mainly as CagriSema). Their trials report large average weight loss ^{[9] [15]}, but neither is approved, and some of retatrutide’s phase 3 data are so far only in company announcements ^[10].

Tier 3, human trials that do not support weight loss: tesamorelin, which reduces visceral fat in HIV but is weight-neutral ^[19], and AOD-9604, whose largest trial failed ^[21].

Tier 4, animal and cell evidence only: MOTS-c, 5-amino-1MQ and SLU-PP-332 ^{[23] [26] [29]}. MOTS-c has a phase 2a trial under way ^[25]; the other two have no registered human trial.

Two cautions apply to every tier. Figures from separate trials cannot be compared directly, because the trials differ in length, dose and who took part; the 2026 network meta-analysis made this point about the GLP-1 family ^[13]. And the trial results describe the manufacturers’ products, not research-labelled vials of uncertain content.

The figures below are the doses trials used or labels approve. They are reported as research findings, not as a recommendation, and PepFinder does not advise on dosing.

Semaglutide was studied at 2.4 mg once weekly by injection in STEP 1 ^[2]. The US Wegovy label starts at 0.25 mg weekly, increases gradually, and gives maintenance doses of 1.7 mg or 2.4 mg, with up to 7.2 mg weekly in some adults; the Wegovy tablet reaches 25 mg daily ^[32]. Tirzepatide was studied at 5 mg, 10 mg and 15 mg weekly ^[3]; the US Zepbound label starts at 2.5 mg weekly and gives maintenance doses of 5 mg, 10 mg or 15 mg ^[33].

Retatrutide has no approved dose. Its phase 2 obesity trial tested 1 mg to 12 mg once weekly ^[9], and the phase 3 trials use 4 mg, 9 mg and 12 mg ^[10]. Cagrilintide alone was tested at 0.3 mg to 4.5 mg once weekly ^[14]; the phase 3 CagriSema trials used 2.4 mg with semaglutide 2.4 mg ^[15].

Tesamorelin was given at 2 mg daily in the phase 3 trials ^[18]; the current US formulation, Egrifta WR, is labelled at 1.28 mg daily ^[19]. AOD-9604 was given by mouth at 0.25 mg to 1 mg daily in its failed 24-week trial ^[21]. MOTS-c, 5-amino-1MQ and SLU-PP-332 have only animal doses in mg/kg ^{[23] [26] [29]}, which should not be converted into human doses.

Milligram figures are not interchangeable between these compounds, which differ in potency and in how long they last. For research vials, our peptide calculator works out concentration from vial size and diluent volume; that is arithmetic, not a dose.

For the GLP-1 family, the most common side effects are gastrointestinal: nausea, diarrhoea, vomiting and constipation, mostly during dose increases. In the pooled Wegovy weight trials, nausea affected 44% on semaglutide 2.4 mg against 16% on placebo ^[32]; in the pooled Zepbound trials, 25% to 29% on tirzepatide against 8% ^[33]. In SURMOUNT-1, 4.3% to 7.1% stopped tirzepatide because of adverse events, against 2.6% on placebo ^[3].

Both US labels carry a boxed warning because the drugs caused thyroid C-cell tumours in rodents; whether this happens in humans is not known. The labels also warn about pancreatitis, gallbladder disease, kidney injury from dehydration and serious allergic reactions ^{[32] [33]}. The MHRA notes very rare reports linking semaglutide to an eye condition called NAION ^[34].

Retatrutide’s side effects come from trials only. In the phase 2 trial, gastrointestinal events were dose-related and heart rate rose in a dose-dependent way before declining ^[9]. Lilly reported nausea in up to 42.4% on 12 mg in TRIUMPH-1, against 14.8% on placebo ^[10]. For cagrilintide alone, nausea affected 20% to 47% depending on dose, against 18% on placebo ^[14].

Tesamorelin’s label lists joint pain, injection-site reactions, pain in the limbs, swelling and muscle pain; diabetes developed in 5% against 1% on placebo ^[19]. AOD-9604’s oral trials reported headache, diarrhoea and flatulence, and the FDA found no safety data for injection under the skin ^[21]. For MOTS-c, 5-amino-1MQ and SLU-PP-332 there are no human safety data at all. A 2026 review of unapproved peptides marketed in sports medicine found rigorous human safety data scarce ^[37].

Independent tests suggest often not. In a 2024 study, semaglutide ordered from illegal online pharmacies arrived as vials whose measured purity was 7.7% to 14.4% against a claimed 99%, with bacterial endotoxin in every sample ^[36]. A 2026 Australian analysis of three products each labelled as 10 mg of retatrutide found 5.13 mg, 19.0 mg and 16.5 mg ^[12].

Regulators have said the same. The MHRA states that licensed GLP-1 medicines come as prefilled pens or tablets and that powder in vials to be mixed before injection is not authorised ^[34]. In the US, the FDA has warned about semaglutide, tirzepatide and retatrutide sold falsely labelled as for research purposes ^[35]. None of the trial results on this page can be assumed to apply to such products.

The GLP-1 medicines have randomised withdrawal trials, and they show weight returning. In STEP 4, people who had lost 10.6% on semaglutide over 20 weeks and were switched to placebo regained 6.9% over the next 48 weeks, while those who continued lost a further 7.9% ^[6]. In SURMOUNT-4, people who had lost 20.9% over 36 weeks on tirzepatide and were switched to placebo regained 14.0% over 52 weeks ^[7]. Tesamorelin’s effect on visceral fat also reversed after stopping ^[20].

Searches for peptides for weight loss and muscle gain combine two goals that the trials above did not test together. The GLP-1 trials measured total body weight as their main outcome ^{[2] [3]}, and none of the compounds on this page has been shown to build muscle while reducing weight in people.

The closest human data are for tesamorelin: in its phase 3 trials, lean body mass rose by about 1.2 to 1.3 kg more than on placebo, in people with HIV ^[19]. The other claims are animal findings. MOTS-c improved running capacity in mice of all ages ^[38], and SLU-PP-332 increased endurance in mice ^[29], but neither has been tested for muscle in people. Growth hormone-releasing peptides marketed for muscle, such as ipamorelin, are covered on their own pages.

Searches for peptides for weight loss women often ask whether anything differs by sex. The licensed trials enrolled both women and men, and their results are reported for everyone together ^{[2] [3]}. The practical differences are about pregnancy and contraception, and they come from the labels and the regulator.

The MHRA advises stopping semaglutide at least 2 months, and tirzepatide at least 1 month, before a planned pregnancy ^[34]. The tirzepatide labels advise people who use oral contraceptives to switch to a non-oral method, or add a barrier method, for 4 weeks after starting and after each dose increase, because tirzepatide may reduce how well the pill works ^{[33] [34]}. Tesamorelin is contraindicated in pregnancy ^[19]. The MOTS-c menopause-model study was in mice ^[24], and no human study has tested MOTS-c in women.

Most peptides are broken down in the gut, which is why nearly all the weight-loss trials used injections. Semaglutide is the exception with human evidence. The tablets contain an absorption enhancer, and even so only about 0.4% to 1% of a Rybelsus dose reaches the bloodstream, so tablet doses are several milligrams a day while injections are a few milligrams a week ^[41]. In OASIS 4, oral semaglutide 25 mg daily produced 13.6% average weight loss at 64 weeks ^[5]. The MHRA approved the Wegovy tablet for weight management in the UK in June 2026 ^[42].

For the other oral peptides for weight loss sold online, the evidence is weak or negative. AOD-9604 was tested by mouth in people and failed ^[21]. In mice, only 3.5% of an oral dose of 5-amino-1MQ reached the blood ^[27], and SLU-PP-332’s developers say it lacks oral bioavailability ^[30]. There are no published human absorption data for oral MOTS-c, 5-amino-1MQ or SLU-PP-332 capsules.

GLP-1, amylin and MOTS-c are natural peptides the body makes, but the drugs studied in trials are modified versions designed to last longer: semaglutide was altered so it survives about a week in the blood rather than minutes ^[1], and cagrilintide was built as a stable, long-acting form of amylin ^[14]. Eating foods or supplements does not deliver these molecules.

Collagen peptides sold as powders are a different thing again. They are hydrolysed protein from animal collagen, sold as food supplements and digested like other dietary protein. None of the trials on this page tested them, and they are unrelated to GLP-1 medicines.

In the UK, semaglutide (Wegovy, Ozempic, Rybelsus) and tirzepatide (Mounjaro) are licensed prescription-only medicines. The MHRA says selling them through unregulated channels is against the law, and advises consulting a healthcare professional before switching from one GLP-1 medicine to another ^[34]. Retatrutide is not approved for UK use, and the MHRA says products claiming to contain it outside authorised trials are likely to be illegal ^[39]. See our UK legal status page.

In the US, semaglutide and tirzepatide are FDA-approved prescription medicines ^{[32] [33]}. Tesamorelin is approved only for HIV-associated abdominal fat ^[19]. The FDA states that retatrutide and cagrilintide are not components of any approved drug ^[35], and its pharmacy compounding advisory committee voted 12 to 0 against adding AOD-9604 to the list of substances pharmacies may use ^{[43] [21]}. MOTS-c, 5-amino-1MQ and SLU-PP-332 are not approved medicines. See our US legal status page and the legal status overview for other countries.

PepFinder does not sell any of these products. We track research-labelled listings so that buyers can compare price and testing in one place. Price pages exist for semaglutide, tirzepatide, retatrutide, cagrilintide, tesamorelin, AOD-9604, MOTS-c, 5-amino-1MQ and SLU-PP-332, with UK-specific listings such as retatrutide UK prices.

Because published tests found content from about half to nearly double the label ^[12], price per milligram means little without a batch-specific certificate of analysis. Our guides to reading a certificate of analysis, third-party testing and how to spot a fake peptide supplier explain what to check, and you can filter for third-party tested suppliers. How peptide prices work explains why per-milligram prices vary.

How we assess suppliers is set out in our methodology. Nothing on this page is medical advice (see our disclaimer); decisions about licensed weight-loss medicines sit with a prescriber.