Goal page
Peptides studied for weight loss
Two compounds in our data have randomised weight loss trials in people: tirzepatide and retatrutide. Tirzepatide is an FDA approved prescription drug. In its main obesity trial, average weight fell 15 to 20.9 percent over 72 weeks against 3.1 percent on placebo, and a follow up trial shows the loss reverses when the drug stops. Retatrutide is still in trials. Its published phase 2 study reported up to 24.2 percent at 48 weeks, the largest figure in the class, but its pivotal obesity results so far exist only in company press releases.
Byline: Mark Sommers, editor. Sources checked 08-24-2026. Every study below links to its PubMed record. We do not publish amounts or schedules.
Approval status varies on this page. At least one compound here is an FDA approved prescription medicine; the rest are not approved for any use, and each entry below says where it stands. This page tells you what has been studied. It does not tell you to use anything, how much, or how often. That belongs with a licensed doctor. Why we draw that line.
How we ranked these, before you see the ranking
The order below is arithmetic, not opinion. Each peptide gets four scores out of 100, and they are added up with fixed weights. Every score on this page is shown, so you can check the sum yourself or decide the weights are wrong.
- Evidence strength, 40 percent. The strongest single study we found for this goal. A randomised trial in people scores 100, a systematic review 75, a small human study 50, a review article 30, an animal study 25, cells in a dish 10.
- Human data, 25 percent. How many of the studies for this goal were done in people. None scores 0, one scores 40, two 60, three 80, four or more 100.
- Safety record, 20 percent. An FDA approved drug with a full label and years of market surveillance scores 100. Some human safety reporting scores 70. Animal safety data only scores 35. No human safety data found scores 10.
- Regulatory clarity, 15 percent. An FDA approved drug scores 100. A drug in FDA trials but not yet approved scores 60. A substance on the FDA list of compounding nominations that were withdrawn scores 25. If the FDA also says it found no human exposure data, it scores 10.
Read the evidence score carefully. It measures how strong the study was, not how well the peptide worked. A well run trial that found nothing scores 100 here. The finding column tells you what it actually found, and on this site a well run trial that found nothing is the most useful kind of result there is.
Full rules and any changes to them: How we check.
The ranking
Sorted by total score. Every number that went into the total is in the row.
| Score | Peptide | Evidence 40% | Human data 25% | Safety 20% | Regulatory 15% | Strongest study we found |
|---|---|---|---|---|---|---|
| 100#1 | Tirzepatide An approved drug with randomised weight loss trials in thousands of people, including head to head and stopping trials. | 100evidence | 100human data | 100safety | 100regulatory | Human trial In adults with obesity and without diabetes, average body weight fell 15.0 to 20.9% over 72 weeks versus 3.1% on placebo, and 85 to 91% lost at least 5% of their starting weight. (n = 2539) |
| 83#2 | Retatrutide The largest published early trial weight loss in the class, but not yet approved, with pivotal results still unpublished. | 100evidence | 80human data | 70safety | 60regulatory | Human trial Over 48 weeks, adults with obesity lost about 8.7% of body weight in the lowest dose group and about 24.2% in the highest, against 2.1% on placebo, and 83% of the highest dose group lost at least 15% of their weight. (n = 338) |
What counts as this goal: Randomised trials in people that measured body weight change as a primary or major outcome.
How to read the study tags
Cells in a dish means it never touched a living animal. Animals means mice or rats, usually. Small human study means a handful of people with no comparison group. Human trial means people were randomly split into treated and untreated groups, which is the only kind that can show an effect is real. Review and Systematic review sum up other studies. The full rule is on How we check.
Tirzepatide
A weekly injection that activates the GLP-1 and GIP receptors. It is an FDA approved prescription drug for type 2 diabetes and for weight management.
Score for this goal: 100 out of 100. The math: (100 x 40 + 100 x 25 + 100 x 20 + 100 x 15) divided by 100 = 100.
Safety, before the studies
FDA approved with a full label and years of market surveillance. Trials show mostly gut side effects, concentrated in the first months, and stopping for side effects ran a few points above placebo. The label carries the serious warnings. Read the label, not a summary of it.
Approved by the FDA. We do not publish amounts or schedules for any of it.
What has been studied for weight loss
| Who or what was studied | What was found, and the catch | Source |
|---|---|---|
| Human trial n = 2539 people | In adults with obesity and without diabetes, average body weight fell 15.0 to 20.9% over 72 weeks versus 3.1% on placebo, and 85 to 91% lost at least 5% of their starting weight. Limit: People with diabetes were excluded, so these numbers do not carry over to them; the companion trial in people with diabetes produced clearly smaller losses. Placebo comparator. 72 weeks says nothing about year five. Blinding is fragile when one group visibly loses a fifth of its body weight. Stopping for side effects was 4.3 to 7.1% versus 2.6% on placebo. Eli Lilly funded. | Jastreboff 2022 PMID 35658024 |
| Human trial n = 938 people | In adults who had both obesity and type 2 diabetes, body weight fell 12.8 to 14.7% over 72 weeks versus 3.2% on placebo. Limit: Weight loss here was noticeably smaller than in people without diabetes, and that is the honest comparison to hold against the widely quoted obesity numbers. Placebo comparator. Only the two higher dose levels were tested, so the lowest is unstudied in this group. 72 weeks. Eli Lilly funded. | Garvey 2023 PMID 37385275 |
| Human trial n = 670 people | After 36 weeks of open label treatment that produced about 21% weight loss, people switched to placebo gained back enough to end 14.0% heavier over the following 52 weeks, while those who kept taking the drug lost a further 5.5%. Limit: This is the trial that shows the benefit depends on staying on the drug indefinitely, and no trial has tested beyond 176 weeks. The first 36 weeks were open label, and only people who tolerated treatment reached randomization, so the randomized group is a filtered, tolerant population. It compares continuing with abrupt stopping, and says nothing about whether a gradual taper or a structured maintenance plan would land differently. Eli Lilly funded. | Aronne 2024 PMID 38078870 |
| Human trial n = 751 people | Head to head against a once weekly GLP-1 only drug over 72 weeks in adults with obesity and no diabetes, weight fell 20.2% versus 13.7%, and waist circumference fell 18.4 cm versus 13.0 cm. Limit: Open label, and weight related outcomes plus side effect reporting are exactly the things knowing your assignment can shift. Phase 3b, designed and funded by the company that makes the winning drug. People with diabetes were excluded. 72 weeks, so nothing here speaks to durability. | Aronne 2025 PMID 40353578 |
| Human trial n = 1032 people | Among the participants who had obesity plus prediabetes, weight was still down 12.3 to 19.7% at 176 weeks versus 1.3% on placebo, and 1.3% had developed type 2 diabetes versus 13.3%, a gap that held after 17 weeks off treatment. Limit: This covers only the prediabetes subgroup, 1032 of the 2539 people in the parent trial, and diabetes onset was a key secondary endpoint rather than the trial's main question. Three years plus is the longest randomized human exposure published for this drug, which means long term thyroid, pancreas and gallbladder outcomes past about four years are simply not established. Eli Lilly funded. | Jastreboff 2025 PMID 39536238 |
Most cited author in this list: Jastreboff, 2 of 5 sources. When a small number of groups produce most of the evidence, independent replication is thinner than the source count suggests.
Retatrutide
A weekly injection that activates three gut hormone receptors at once: GLP-1, GIP and glucagon. It is in FDA trials for obesity and diabetes and is not approved or sold as a medicine.
Score for this goal: 83 out of 100. The math: (100 x 40 + 80 x 25 + 70 x 20 + 60 x 15) divided by 100 = 83.
Safety, before the studies
Some human safety reporting exists. Trial safety reporting covers several thousand participants. The published pattern is gut side effects and a heart rate rise that climb with the amount, plus a nerve sensation signal at the top trial level that has no peer reviewed report yet.
In FDA trials but not yet approved. We do not publish amounts or schedules for any of it.
What has been studied for weight loss
| Who or what was studied | What was found, and the catch | Source |
|---|---|---|
| Human trial n = 338 people | Over 48 weeks, adults with obesity lost about 8.7% of body weight in the lowest dose group and about 24.2% in the highest, against 2.1% on placebo, and 83% of the highest dose group lost at least 15% of their weight. Limit: This is the trial the whole reputation rests on, and it is one trial, run and funded by Eli Lilly, with Lilly employees on the author list. It ran 48 weeks, so nothing here says what happens after that. Heart rate rose in a dose related way, peaking at 24 weeks. No independent group has ever repeated it. | Jastreboff 2023 PMID 37366315 |
| Small human study n = 103 people | DXA scans in a slice of the diabetes trial showed fat mass fell substantially in the higher dose groups, with no significant change in the lowest dose group. Limit: Only 103 of the 189 people enrolled in the substudy had scans at both the start and the end, so more than 40% are missing and it is not random who dropped out. It is a substudy of an already published Lilly trial. The lead author is a Lilly employee who appears on 12 of the 16 retatrutide papers. | Coskun 2025 PMID 40609566 |
| Small human study | Retatrutide slows how fast the stomach empties, the same mechanism that makes gut hormone drugs curb appetite and that can change how other swallowed medicines are absorbed. Limit: PubMed carries no abstract for this paper and the full text is paywalled. The only thing that can be verified is the claim in the title. No participant count, no effect size, no time course. Nobody has published how much this matters for other drugs a person might take. | Urva 2023 PMID 37311727 |
What is missing
- Retatrutide's pivotal phase 3 obesity trials have reported results only in Eli Lilly press releases. Not one has a peer reviewed publication yet.
- Every trial on this page was funded by Eli Lilly, which makes both drugs. No independent group has replicated any of these results.
- Weight regain after stopping is documented for tirzepatide and unstudied for retatrutide. Nothing on this page speaks to year five for either.
What this page does not cover, and why
Other approved weight loss medicines, including the GLP-1 only drugs these two were tested against in the trials above, are prescription products a doctor should compare for you. And the research peptides sometimes sold for weight loss have no weight loss trials we could rank. We do not add a compound to a goal page until we have read its studies.
Sources
- Aronne (2024). PMID 38078870
- Aronne (2025). PMID 40353578
- Coskun (2025). PMID 40609566
- Garvey (2023). PMID 37385275
- Jastreboff (2022). PMID 35658024
- Jastreboff (2023). PMID 37366315
- Jastreboff (2025). PMID 39536238
- Urva (2023). PMID 37311727
FDA list of bulk drug substances nominated for compounding and withdrawn, last checked 08-24-2026: fda.gov. Every claim above is also on our evidence table.
Other goals
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Studies about skin appearance, collagen, scalp and hair, in people or in human skin cells.
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Studies about inflammation of the bowel, in animals or in cells.
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