When people search for the “best peptides for weight loss,” they usually want a ranked list that tells them what to take. This page deliberately does something more useful and more honest: it summarizes which peptides have been most studied and most discussed in the context of body weight, and — most importantly — what the human evidence actually shows for each one. “Most studied” is not the same as “proven to work,” and neither is the same as “right or safe for you.” Nothing here is a recommendation to use, buy, or dose any compound.
The context that matters up front: the compounds below sit at very different levels of evidence. A couple have large randomized Phase 3 trials and regulatory approval behind them; others have only early-phase human data, data collected for a completely different purpose, or nothing beyond animal studies. All information on this page is provided for research and educational purposes only (research-use-only) and is not medical advice. The evidence cited below is drawn from peer-reviewed studies indexed on PubMed.
Comparison at a glance
| Peptide | What it’s studied for (re: weight loss) | Evidence tier | Key caveat |
|---|---|---|---|
| Semaglutide | GLP-1 receptor agonist; body-weight reduction in adults with overweight/obesity | Strong — large Phase 3 RCTs; approved for chronic weight management | Gastrointestinal side effects; weight tends to return after stopping |
| Tirzepatide | GIP/GLP-1 dual agonist; body-weight reduction | Strong — large Phase 3 RCTs; approved for chronic weight management | GI side effects; long-term outcome data still accruing |
| Retatrutide | GIP/GLP-1/glucagon triple agonist; body-weight reduction | Moderate — Phase 2 only; Phase 3 ongoing, not approved | Not yet confirmed in Phase 3; safety profile still under study |
| Cagrilintide | Long-acting amylin analogue; body-weight reduction alone and with semaglutide | Moderate — Phase 1b/Phase 2; not approved as a standalone | Strongest data are the combination with semaglutide, not monotherapy |
| Tesamorelin | GHRH analogue; reduces visceral (abdominal) fat | Human clinical but narrow — approved only for HIV-associated lipodystrophy | Reduces visceral fat, not overall body weight; not studied for general weight loss |
| AOD-9604 | Growth-hormone fragment; weight/fat loss in animal models | Weak — preclinical/animal; no published human efficacy | No peer-reviewed human obesity trial has shown it produces weight loss |
Semaglutide
Semaglutide is the most robustly studied compound on this list for weight specifically. In the STEP 1 Phase 3 randomized trial, adults with overweight or obesity lost a mean of 14.9% of body weight over 68 weeks versus 2.4% with placebo (Wilding et al., NEJM 2021). A separate trial showed that weight loss was largely regained after treatment was stopped (Rubino et al., JAMA 2021), underscoring that the effect depends on continued use rather than being permanent. Common side effects are gastrointestinal. This is educational context, not a suggestion to use it — see the semaglutide dosage reference for how researchers describe the compound.
Tirzepatide
Tirzepatide showed the largest average reductions among the approved options. In the SURMOUNT-1 Phase 3 trial, mean weight change at 72 weeks was −15.0%, −19.5% and −20.9% at the 5 mg, 10 mg and 15 mg doses respectively, versus −3.1% with placebo (Jastreboff et al., NEJM 2022). Like semaglutide, effects are tied to ongoing use and the most common adverse events are gastrointestinal, mostly during dose escalation. Long-term cardiovascular-outcome data are still being generated. Compound details are catalogued in the tirzepatide dosage reference.
Retatrutide
Retatrutide is an investigational triple agonist that produced striking numbers in a Phase 2 trial: mean weight reduction of 24.2% at the 12 mg dose at 48 weeks versus 2.1% with placebo (Jastreboff et al., NEJM 2023). The honest caveat is important: this is Phase 2 data in 338 participants, not the large Phase 3 confirmation used for approval, and the safety profile is still being characterized. Promising is not the same as proven. Background is compiled in the retatrutide dosage reference.
Cagrilintide
Cagrilintide is a long-acting amylin analogue. As a standalone in a Phase 2 dose-finding trial, weekly doses produced weight reductions of roughly 6.0%–10.8% at 26 weeks versus 3.0% with placebo (Lau et al., Lancet 2021). Its most-discussed use is combined with semaglutide (the “CagriSema” combination), where an early Phase 1b study reported around 15%–17% weight loss at 20 weeks (Enebo et al., Lancet 2021). It is not approved as a standalone weight-loss product, and the standalone dataset is smaller than for the GLP-1 drugs above. See the cagrilintide dosage reference.
Tesamorelin
Tesamorelin is frequently listed among “weight-loss peptides,” but the evidence does not support that framing. It is a growth-hormone-releasing-hormone analogue approved only to reduce excess visceral abdominal fat in people with HIV-associated lipodystrophy. In those trials it reduced visceral adipose tissue but did not meaningfully change overall body weight, and it has not been studied or approved for general weight loss (Dhillon, Drugs 2011). In other words, its human data are about fat distribution in a specific medical population, not weight loss in the general sense people usually mean. Details are in the tesamorelin dosage reference.
AOD-9604
AOD-9604 is a synthetic fragment of human growth hormone (residues 176–191). In obese mice, it reduced body weight and body fat over chronic dosing (Heffernan et al., Endocrinology 2001). That is genuinely interesting mechanistically — but it is animal data. There are no published peer-reviewed randomized trials showing that AOD-9604 produces meaningful weight loss in humans, and its clinical development for obesity did not lead to an approved product. Its human weight-loss efficacy should be considered unproven. The AOD-9604 dosage reference catalogues the compound for research context only. Detailed side-by-side comparisons are in AOD-9604 vs semaglutide and AOD-9604 vs tesamorelin.
What the evidence actually supports
Reading the evidence honestly, the compounds fall into clear tiers:
- Best-evidenced for weight loss: semaglutide and tirzepatide. Both have large Phase 3 randomized trials and regulatory approval for chronic weight management. If “most studied and best-established” is the question, these two are the answer.
- Promising but not confirmed: retatrutide and cagrilintide. Both show meaningful weight reduction in early-phase human trials, but neither has completed the Phase 3 confirmation and approval process as a standalone weight-loss agent.
- A different target entirely: tesamorelin. Its human evidence is about reducing visceral fat in a specific condition, not overall weight loss — so ranking it as a “weight-loss peptide” misrepresents the data.
- Weak or unstudied in humans: AOD-9604. Its weight-loss evidence is preclinical/animal; there is no published human efficacy to inflate.
Higher numbers in a single trial also do not mean a compound is “better” for any individual — trial averages describe a study population under monitoring, not what will happen to a given person.
How fast does the weight come off?
The trials answer this more precisely than most summaries do. Change is gradual, it tracks a deliberately slow dose escalation, and most of the average reduction accumulates over the first nine to twelve months rather than the first few weeks.
| Compound | Trial length | Mean weight change | Time to reach the study dose |
|---|---|---|---|
| Semaglutide (injection, 2.4 mg weekly) | 68 weeks | −14.9% vs −2.4% placebo | about 16 weeks of stepped escalation |
| Semaglutide (oral, 25 mg daily) | 64 weeks | −16.6% vs −2.7% placebo | stepped escalation over the opening months |
| Tirzepatide (15 mg weekly) | 72 weeks | −20.9% vs −3.1% placebo | about 20 weeks of stepped escalation |
| Retatrutide (12 mg weekly, investigational) | 48 weeks | −24.2% vs −2.1% placebo | stepped escalation |
| Cagrilintide (weekly, standalone) | 26 weeks | −6.0% to −10.8% vs −3.0% placebo | stepped escalation |
| Tesamorelin (daily) | 26 weeks | visceral fat about −15%; body weight largely unchanged | fixed daily dose |
Two things follow from that shape. First, the headline percentages belong to people who stayed on treatment for more than a year under medical supervision alongside diet and activity changes — they are not a six-week outcome. Second, the curves flatten: in STEP 1 the average kept falling for roughly the first year and then levelled off. A longer timeline breakdown for one compound is set out in how long semaglutide takes to work.
What happens after stopping belongs to the same picture. When semaglutide was withdrawn in a controlled trial, most of the lost weight returned (Rubino et al., JAMA 2021, cited above). These are chronic-treatment results, not a course someone finishes.
Side effects reported in the trials
| Compound | Most commonly reported | What the label or the trial reports flag |
|---|---|---|
| Semaglutide, tirzepatide | Nausea, vomiting, diarrhoea, constipation — mostly mild to moderate and concentrated during dose escalation | Gallbladder events; pancreatitis reported rarely; a boxed warning about thyroid C-cell tumours seen in rodents, with use contraindicated where there is a personal or family history of medullary thyroid carcinoma or MEN 2 |
| Retatrutide | Gastrointestinal events, dose-dependent | Dose-dependent increases in heart rate were reported in Phase 2; there is no label, because it is not approved |
| Cagrilintide | Gastrointestinal events, injection-site reactions | The standalone dataset is small and it is not approved as a standalone product |
| Tesamorelin | Injection-site reactions, joint pain, fluid retention | Raises IGF-1 and can affect glucose handling, which is why its approved use is medically supervised and monitored |
| AOD-9604 | No large human safety dataset exists | An absence of reported problems in small studies is not the same as an established safety profile |
The pattern matters as much as the list. For the GLP-1-based compounds the complaints cluster in the escalation phase and ease afterwards for most participants, which is precisely why the trials raised the dose so slowly. A fuller breakdown for one compound is in semaglutide side effects. None of the above is a complete safety profile, and none of it replaces a prescriber who knows an individual’s history.
Injection, pill, or research-grade powder?
Format is now a real distinction rather than a detail. Semaglutide exists as a weekly injection and, since the FDA cleared an oral formulation for chronic weight management, as a once-daily tablet; the oral Phase 3 programme (OASIS 4) reported roughly 16.6% mean weight loss versus 2.7% with placebo. Small-molecule oral GLP-1 candidates such as orforglipron are still in late-stage trials — the three are set side by side in orforglipron vs semaglutide vs tirzepatide.
Research-grade material is a different category entirely. A vial sold for laboratory use is not a prescription product: its identity, purity and sterility are not verified by a regulator, and none of the trial results on this page were generated with it. Everything above describes pharmaceutical product studied under supervision, which is exactly why this page reports what was found rather than telling anyone what to take.
Important limitations
- Everything here is provided for research and educational purposes only and is not medical advice, diagnosis, or a treatment recommendation.
- Most peptides on this page are not approved for weight loss. Several are investigational, approved only for an unrelated condition, or unproven in humans.
- Efficacy figures come from specific study populations under medical supervision. Individual results, eligibility, and safety are unknown and can differ substantially — including serious risks not visible in short trials.
- Weight changes in these trials generally depend on continued use and were studied alongside lifestyle measures.
- Decisions about any of these compounds are medical questions. Consult a qualified healthcare professional. To explore how researchers describe reconstitution and measurement, you can use the peptide dosage calculator — a reference tool, not an endorsement to use any substance.
FAQ
Which peptide showed the most weight loss in studies?
In the trial data, tirzepatide and the investigational retatrutide showed the largest average reductions (about 21% and 24% at their top doses in their respective trials), while semaglutide showed roughly 15%. But a bigger number in one trial does not mean a compound is safer or right for any individual, and retatrutide is not approved. This is research context, not a ranking of what anyone should take.
Are any of these actually approved for weight loss?
Only semaglutide and tirzepatide are approved for chronic weight management. Retatrutide and cagrilintide are investigational, tesamorelin is approved for a different condition (HIV-associated visceral fat), and AOD-9604 is not an approved weight-loss product and lacks published human efficacy.
Is “most studied” the same as “best for me”?
No. Evidence tells you what happened, on average, in a monitored study population. It cannot tell you what will happen to you, whether a compound is appropriate for your situation, or whether it is safe for you. Those are individual medical questions for a qualified professional — which is exactly why this page is educational and research-use-only rather than a recommendation.
How long before the weight starts coming off?
In the trials the dose was raised in steps over roughly the first four to five months, and the average weight curve fell steadily across that period and beyond. Most of the reported reduction accumulated over the first nine to twelve months, not the first few weeks. Individual response varied widely around those averages.
What happens if someone stops?
In a controlled withdrawal trial of semaglutide, most of the lost weight was regained after treatment stopped (Rubino et al., JAMA 2021). The trial evidence describes ongoing treatment, so results should not be read as a permanent change that persists once the compound is discontinued.
Which one has the fewest side effects?
There is no head-to-head trial that answers this cleanly, and comparing adverse-event rates across different trials with different populations is not reliable. What the reports do show is a pattern: gastrointestinal effects dominate for the GLP-1-based compounds and are concentrated during dose escalation, while tesamorelin’s documented issues are injection-site reactions, joint pain, fluid retention and effects on IGF-1 and glucose handling.
Is a research-grade vial the same thing as the prescription version?
No. Research-grade material is sold for laboratory use, and its identity, purity and sterility are not verified by a medicines regulator. Every efficacy and safety figure on this page comes from trials that used pharmaceutical product under medical supervision, so those numbers cannot be transferred to a research vial.
