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Best Peptides for Weight Loss: What the Evidence Shows

Which peptides have evidence for weight loss? FDA-approved vs investigational, with the trials and the criteria. Educational, not medical advice.

By Best Peptides For Editorial Team · Updated

U.S. status verified:

The short answer

Among the peptides we reviewed, the options with the strongest evidence for weight loss are semaglutide (Wegovy) and tirzepatide (Zepbound): both are FDA-approved for weight reduction, and both have large randomized trials. Retatrutide has strong published results but is not approved and, according to FDA, cannot be compounded. Nothing else we reviewed for this guide has human evidence of weight loss.

This guide does not yet cover every peptide with human weight-loss evidence. Liraglutide (Saxenda) is FDA-approved for weight reduction in the group named on its label, and we have not reviewed its trials here. Setmelanotide is covered below, for the rare forms of obesity its label names.

Whether any of these is right for you is a decision for a prescriber.

On this page

“Best” here means best evidence, not best marketing. Among the peptides we reviewed, two FDA-approved drugs lead on evidence, one promising drug is still unapproved, and several popular “fat-burning” peptides have no weight-loss trial behind them.

The ranking, by strength of evidence

Ordered by the strength of the evidence that it helps with this goal: the type of study first, then its quality and its result. A rank isn’t a recommendation.
PeptideU.S. statusStrongest evidence
1. Semaglutide FDA-approvedFor long-term weight management in adults with obesity, or overweight plus a weight-related condition, and in children 12 and older with obesityCompounded versions: not FDA-approved Human trials
2. Tirzepatide FDA-approvedFor weight reduction and maintenance in adults with obesity, or overweight plus a weight-related conditionCompounded versions: not FDA-approved Human trials
3. Retatrutide Investigational Human trials
4. Setmelanotide FDA-approvedFor weight reduction and maintenance in acquired hypothalamic obesity, Bardet-Biedl syndrome, and POMC, PCSK1 or LEPR deficiency confirmed by genetic testing Human trials
5. Tesamorelin FDA-approvedFor other uses Human trials
6. CJC-1295 and ipamorelin Not FDA-approved Limited human data

How do we decide what is “best”?

We rank by evidence. For each peptide we ask:

  1. Is there a randomized, controlled trial in people, with weight measured directly?
  2. Is it published in a peer-reviewed journal, or only announced by the company?
  3. Does FDA approve it for this use, and what does the label warn about?
  4. Who funded the trial, and was the comparison fair?
  5. What do we know about safety, and for how long?

Animal studies, lab studies and hormone levels alone do not count as evidence of weight loss in humans.

Which peptides have evidence for weight loss?

SemaglutideTirzepatideRetatrutide
FDA status for weightApproved (Wegovy)Approved (Zepbound)Not approved (investigational)
Best human evidenceSTEP 1: 1,961 adults, 68 weeksSURMOUNT-1: 2,539 adults, 72 weeksTRIUMPH-1: 2,339 adults, 80 weeks
Study typeRandomized, placebo-controlledRandomized, placebo-controlledRandomized, placebo-controlled, phase 3
Average weight change−14.9% vs −2.4%−15.0% to −20.9% vs −3.1% (by dose arm)−17.6% to −25.0% vs −3.9% (by dose arm)
Compounded versionsNot FDA-approvedNot FDA-approvedFDA: cannot be used in compounding
Main caveatBoxed warning: thyroid C-cell tumors (rodents)Same boxed warningNo label; long-term safety unknown

Do not read across the columns as a ranking. These are three separate trials with different participants and designs. A direct comparison is below.

Is semaglutide or tirzepatide better for weight loss?

In adults without diabetes, the direct comparison is SURMOUNT-5 (751 adults with obesity, 72 weeks, open-label, funded by Lilly): tirzepatide produced −20.2% weight loss and semaglutide −13.7%. An earlier Lilly-funded, open-label trial in type 2 diabetes, SURPASS-2, also favored tirzepatide. SURMOUNT-5 measured weight and waist, not heart attacks. For the full picture, including approved uses and heart-trial differences, see our semaglutide vs tirzepatide comparison, and for the trials behind semaglutide, our semaglutide guide.

What about retatrutide?

Retatrutide is an investigational drug. It is not FDA-approved for any use. The company developing it, Eli Lilly, says it plans to submit an application to FDA in the first quarter of 2027. That is a company plan, not an approval timeline.

What has been published:

  • TRIUMPH-1 (NEJM): in adults with obesity and no diabetes, average weight change at 80 weeks was −17.6%, −23.7% and −25.0% across the three dose arms (low, medium, high), vs −3.9% on placebo.
  • TRIUMPH-2 (Lancet): in adults with obesity and type 2 diabetes, −11.9%, −16.8% and −18.8% vs −5.1%.
  • Phase 2 trial (NEJM, 338 adults, 48 weeks): up to −24.2% vs −2.1%.

Why do you see “28%” in headlines and 25% in the journal?

For TRIUMPH-1, Lilly’s May release gives 28.3% on the highest dose; NEJM reports 25.0%. For TRIUMPH-2, Lilly’s September release gives 20.8%; The Lancet reports 18.8%.

The reason is a statistical choice. Lilly labels its figures the “efficacy estimand,” which it defines as the effect had all randomized participants remained on treatment. The journal figures use the treatment-regimen estimand, which Lilly describes as the average effect regardless of whether people kept taking the drug or started prohibited weight-loss treatments. Lilly’s May release gives the same 25.0% under that estimand. Neither is wrong, and they answer different questions. We use the journal figures here, and a company’s 28% should not be compared with journal figures for other drugs.

Is retatrutide better than tirzepatide?

Unknown. We found no published head-to-head result; a trial of that kind is listed as still active.

Side effects seen in the trials

There is no label, so this comes from the trials. In TRIUMPH-2, nausea occurred in 14%, 21% and 28% across dose arms vs 8% on placebo; low blood pressure in up to 6% vs under 1%; and abnormal skin sensations in up to 7% vs 1%. Stopping because of side effects or death was 4%, 12% and 8% in the low, medium and high arms vs 5% on placebo. Six people across the retatrutide groups and one on placebo died; the investigators deemed the deaths unrelated to treatment. Heart rate rose with dose in the phase 2 trial. Long-term safety is unknown (TRIUMPH-2; phase 2).

Can retatrutide be bought legally?

FDA says: “Retatrutide and cagrilintide cannot be used in compounding under federal law,” and that they “have not been found safe and effective for any condition” (FDA, Oct. 1, 2026). FDA says it has also warned telehealth companies, API distributors and outsourcing facilities over retatrutide. HHS’s Oct. 30, 2026 interim compounding policy does not include retatrutide. There is no FDA-approved retatrutide product to buy. We do not link to or recommend any seller.

Setmelanotide: approved, but only for rare forms of obesity

Setmelanotide is FDA-approved as Imcivree to reduce weight and maintain the reduction in specific, rare conditions: acquired hypothalamic obesity (from age 4), and, from age 2, Bardet-Biedl syndrome or POMC, PCSK1 or LEPR deficiency confirmed by genetic testing (label). The label says it is not indicated for general obesity, where it would not be expected to work. It is not a GLP-1 drug.

The trials are small because the conditions are rare. In TRANSCEND, a 52-week trial in acquired hypothalamic obesity sponsored by the manufacturer, BMI fell 16.5% on setmelanotide and rose 3.3% on placebo; serious adverse events occurred in 28% vs 8%. In Bardet-Biedl and Alström syndromes (38 people, 14 controlled weeks followed by open-label treatment), 32.3% of participants over 12 with Bardet-Biedl syndrome reached at least a 10% weight loss at 52 weeks; the Alström results were inconclusive. Its label also warns of spontaneous erections, depression and suicidal ideation, severe hypersensitivity and skin darkening. We do not compare it with semaglutide or tirzepatide, because the people studied are different.

Are “fat-burning” peptides like CJC-1295 and ipamorelin worth it?

Not on the evidence we have. In small studies of healthy adults, CJC-1295 raised growth hormone and IGF-I levels (2- to 10-fold and 1.5- to 3-fold). Those are hormone markers, not fat loss. We found no published trial of CJC-1295 and ipamorelin taken together, and neither is FDA-approved. Our review of their evidence is in our muscle growth guide.

Tesamorelin: an approved peptide that is not a weight-loss drug

Tesamorelin (Egrifta) is FDA-approved to reduce excess abdominal fat in adults with HIV and lipodystrophy, a specific condition. Its label states it is not indicated for weight loss management. In two pooled phase 3 trials of 806 people with HIV, visceral fat fell by about 15% relative to placebo at 26 weeks (Falutz 2010). Those trials did not test people without HIV.

What about compounded semaglutide and tirzepatide?

They are not FDA-approved, and FDA does not review compounded drugs for safety, effectiveness or quality before they are sold. FDA has said compounded products should not be called “generic” or “the same as” an approved drug (FDA), and neither drug is on the shortage list or the 503B list (FDA). The details and dates are in our semaglutide guide.

What should you ask a doctor?

  • Am I a candidate for an FDA-approved weight-management drug, given my health history?
  • Do I have a personal or family history of medullary thyroid carcinoma or MEN 2? (Both Wegovy and Zepbound are contraindicated in that case.)
  • Which product would I be prescribed, and is it FDA-approved or compounded?
  • What side effects should make me call you?
  • What is the plan if I stop?

Frequently asked questions

What is the best peptide for weight loss?

Among the peptides we reviewed: semaglutide and tirzepatide, both FDA-approved with large randomized trials. Between them, one Lilly-funded, open-label head-to-head trial in adults without diabetes found more weight loss with tirzepatide.

Is retatrutide approved?

No. It is investigational, and FDA says it cannot be used in compounding.

Do BPC-157 or CJC-1295 help with weight loss?

We found no trial showing they do. BPC-157’s human evidence is limited to two controlled studies reported only as abstracts (one on effectiveness in colitis, one phase 1 tolerability study) and a few small uncontrolled reports, none about weight (see our BPC-157 guide).

Can a peptide replace a clinician’s advice?

No. The evidence above comes from trials run under medical supervision, and the approved drugs carry boxed warnings and contraindications that need individual review.

How did we rank them?

We rank by the type of evidence first, then its quality and its result. If no peptide has good evidence for a goal, we say so.

  1. Human trialsControlled trials in people, published in a journal, that tested a clinical outcome and showed a benefit. The strongest kind of evidence we report.
  2. Limited human dataSmall, short or inconclusive human studies, including observational studies, uncontrolled trials and controlled trials that did not show a clinical benefit.
  3. Animal studiesResults in animals often don’t carry over to people.
  4. Lab studiesCells or tissue in a dish. An early signal, not an answer.

Sources we checked

  1. STEP 1 trial (PubMed)PubMed. Accessed .
  2. SURMOUNT-1 trial (PubMed)PubMed. Accessed .
  3. SURMOUNT-5 trial (PubMed)PubMed. Accessed .
  4. SURPASS-2 trial: tirzepatide vs semaglutide in type 2 diabetes (PubMed)PubMed. Accessed .
  5. Saxenda (liraglutide) label (DailyMed)FDA. Accessed .
  6. Imcivree (setmelanotide) prescribing information (DailyMed)FDA. Accessed .
  7. Setmelanotide in acquired hypothalamic obesity, TRANSCEND, NEJM 2026 (PubMed)PubMed. Accessed .
  8. Setmelanotide in Bardet-Biedl and Alström syndromes, Lancet Diabetes Endocrinol 2022 (PubMed)PubMed. Accessed .
  9. TRIUMPH-1 trial, retatrutide (PubMed)PubMed. Accessed .
  10. TRIUMPH-2 trial, retatrutide (PubMed)PubMed. Accessed .
  11. Retatrutide phase 2 trial in obesity (PubMed)PubMed. Accessed .
  12. Lilly press release on retatrutide, Sept. 29, 2026Press release. Accessed .
  13. Lilly press release on retatrutide TRIUMPH-1, May 21, 2026Press release. Accessed .
  14. ClinicalTrials.gov NCT06662383 (retatrutide comparison trial, active)ClinicalTrials.gov. Accessed .
  15. Wegovy prescribing information (DailyMed, rev. 06/2026)FDA. Accessed .
  16. Zepbound prescribing information (DailyMed, rev. 08/2026)FDA. Accessed .
  17. Egrifta WR prescribing information (DailyMed, rev. 03/2025)FDA. Accessed .
  18. Tesamorelin pooled phase 3 trials, Falutz 2010 (PubMed)PubMed. Accessed .
  19. CJC-1295 trials in healthy adults, Teichman 2006 (PubMed)PubMed. Accessed .
  20. FDA's concerns with unapproved GLP-1 drugs used for weight lossFDA. Accessed .
  21. FDA clarifies policies for compounders as national GLP-1 supply stabilizesFDA. Accessed .
  22. FDA: telehealth companies and promoting compounded drugsFDA. Accessed .

Written and maintained by the Best Peptides For Editorial Team. How we rate evidence.