Peptides for Weight Loss: What the Evidence Actually Shows

Ordered by how far the published human evidence goes — strongest first. Availability is a separate question from evidence, so it is labeled separately.

1. 1.Tirzepatide (Zepbound, Mounjaro)

   FDA-approved
   Randomized trials

   Evidence strength: Randomized trials. Randomized controlled trials in humans, at scale.

   ▸Read the full write-up

   What it is

   A single molecule that activates two gut-hormone receptors at once, GIP and GLP-1. It is injected once a week.

   What the evidence shows

   In SURMOUNT-1, 72 weeks of the 15 mg dose produced a mean weight change of −20.9% against −3.1% on placebo, and 91% of people on that dose lost at least 5% of their body weight. A 2026 network meta-analysis of 25 trials put tirzepatide 15 mg first for percentage weight reduction across the whole class.^3,5

   The catch

   Gastrointestinal side effects scale with the dose, and the network meta-analysis found they rose with every drug in this class. It is also the class where stopping means regaining — see semaglutide below, where that was measured directly.

   Approved for this use and available by prescription.

2. 2.Semaglutide (Wegovy, Ozempic)

   FDA-approved
   Randomized trials

   Evidence strength: Randomized trials. Randomized controlled trials in humans, at scale.

   ▸Read the full write-up

   What it is

   A GLP-1 receptor agonist, injected weekly. The most-studied peptide for weight loss by a wide margin.

   What the evidence shows

   STEP 1 ran 1,961 adults for 68 weeks: mean weight change −14.9% on semaglutide 2.4 mg versus −2.4% on placebo, with 50.5% of the treated group losing 15% or more.^1,2

   The catch

   The trial extension followed people after they stopped. A year off the drug, they had regained 11.6 of the percentage points they had lost — a 17.3% loss became a 5.6% loss — and most of the cardiometabolic improvements drifted back toward baseline. That is the number to plan around, not the 14.9%.

   Approved for this use and available by prescription.

3. 3.Cagrilintide + semaglutide (CagriSema)

   Research use only
   Randomized trials

   Evidence strength: Randomized trials. Randomized controlled trials in humans, at scale.

   ▸Read the full write-up

   What it is

   An amylin analog paired with semaglutide, targeting two separate satiety pathways in one weekly injection.

   What the evidence shows

   The 2026 network meta-analysis placed the combination at −17.84% mean weight reduction, essentially level with tirzepatide 15 mg at −17.97%, and ahead of everything else at the 20%-or-more threshold.⁵

   The catch

   Not approved, so there is no legitimate prescription route to it yet. Cagrilintide on its own performed well below the combination — buying the amylin half from a gray-market seller is not a cheap version of this result.

   Sold for laboratory use. Not a legal medicine for people.

4. 4.Tesamorelin (Egrifta)

   FDA-approved
   Randomized trials

   Evidence strength: Randomized trials. Randomized controlled trials in humans, at scale.

   ▸Read the full write-up

   What it is

   A growth-hormone-releasing factor analog, approved for one narrow use: excess visceral abdominal fat in people with HIV-associated lipodystrophy.

   What the evidence shows

   The pivotal NEJM trial found it reduced visceral adipose tissue in that population, which is what its approval covers.⁶

   The catch

   It is approved for a specific condition, not for general weight loss, and it moves visceral fat rather than the number on the scale. If you do not have HIV-associated lipodystrophy, no evidence here applies to you.

   Approved for this use and available by prescription.

5. 5.Retatrutide

   Research use only
   Early human

   Evidence strength: Early human. Small, open-label, or phase 1/2 trials. Promising, unproven.

   ▸Read the full write-up

   What it is

   A triple agonist — GIP, GLP-1 and glucagon receptors — from Eli Lilly. Still investigational, but no longer a phase 2 story: as of August 2026 a ClinicalTrials.gov intervention search for retatrutide returns 33 studies, 14 of them phase 3.

   What the evidence shows

   A phase 2 trial in 338 adults reported a mean −24.2% at 48 weeks on the 12 mg dose against −2.1% on placebo. A phase 3 result has since published: TRANSCEND-T2D-1 gave retatrutide as a monotherapy to 537 adults with type 2 diabetes for 40 weeks and reported a mean −15.3% on 12 mg against −2.6% on placebo, alongside its primary endpoint, a 1.94-percentage-point fall in HbA1c against 0.81 on placebo.^4,9

   The catch

   That phase 3 ran in type 2 diabetes, over 40 weeks, with HbA1c as its primary endpoint and weight as a secondary one, and it reports under a different estimand than the phase 2 trial — so it is not a read on obesity without diabetes and it neither confirms nor refutes the 24.2%. The trials that would are the four TRIUMPH registrational trials, 5,878 participants between them, completed between November 2025 and June 2026; as of August 2026 none of the four has posted results on ClinicalTrials.gov. A published trial is also not an approval — retatrutide has no FDA-approved product for any indication, so nothing you can buy today labeled 'retatrutide' came from Lilly. Wait for it, or take one of the approved options above.

   Sold for laboratory use. Not a legal medicine for people.

6. 6.CJC-1295 and ipamorelin

   Compounding restricted
   Animal only

   Evidence strength: Animal only. Rodent or cell studies. Nothing published in humans.

   ▸Read the full write-up

   What it is

   Two growth-hormone secretagogues, usually sold together as a blend, marketed on the premise that more growth hormone means more fat burned.

   What the evidence shows

   CJC-1295 does what it says on the mechanism: a 2006 trial in healthy adults showed it raises growth hormone and IGF-1 for days after a dose. What no trial shows is that this produces weight loss.^7,8

   The catch

   Raising a hormone is not the same as changing a body. There is no human weight-loss outcome trial for either compound, and peptide compounding is under active FDA restriction — compliant pharmacies decline to sell these.

   Under active FDA restriction — compliant pharmacies decline to sell it.

7. 7.MOTS-c

   Research use only
   Animal only

   Evidence strength: Animal only. Rodent or cell studies. Nothing published in humans.

   ▸Read the full write-up

   What it is

   A peptide encoded in mitochondrial DNA, studied for its effects on metabolism and insulin sensitivity.

   What the evidence shows

   The metabolic work is in rodents and cell models. It appears in the 2026 review of unapproved peptides on exactly that basis — favorable animal metabolic outcomes, scarce human safety data.⁸

   The catch

   Nothing published tells you what it does to body weight in a person. Sold for research use, which is a legal category, not a quality standard.

   Sold for laboratory use. Not a legal medicine for people.

8. 8.AOD-9604

   Research use only
   Anecdotal

   Evidence strength: Anecdotal. User reports and forum consensus. No controlled data.

   ▸Read the full write-up

   What it is

   A fragment of human growth hormone, sold specifically as a fat-loss peptide. The name is short for 'anti-obesity drug 9604.'

   What the evidence shows

   There is no published human weight-loss efficacy trial for it. A 2026 review of unapproved peptides sold direct to patients covers AOD-9604 among compounds where favorable animal results have not been matched by rigorous human data.⁸

   The catch

   A compound named after the outcome it is sold for, with no trial demonstrating that outcome. The same review notes the placebo effect as a real mediator of perceived peptide efficacy, amplified by social media — which is most of what you will find if you search for results.

   Sold for laboratory use. Not a legal medicine for people.