# Peptides for weight loss: three approved ones cut 8% to 21%

URL: https://sciencebased.news/weight-loss-peptides/
Published: 2026-10-20  Updated: 2026-10-27
Claim: Approved peptides like Ozempic cut body weight 8% to 21% in large trials. Grade: Solid

What to do:
- Ask a doctor about the approved ones: semaglutide (Wegovy, also sold as Ozempic for diabetes) or tirzepatide (Zepbound, also sold as Mounjaro). A doctor prescribes them.
- Expect about 15% of body weight off on Wegovy and about 21% on Zepbound in 68 to 72 weeks. Zepbound beat Wegovy head to head, 20.2% against 13.7%.
- Plan to stay on it. People who stopped regained most of the loss within a year. Lift two or three times a week and eat enough protein to keep your muscle.
- Safety: skip vials sold for research use or not for human consumption, retatrutide included. The FDA has warned sellers, and nobody checks what is in them.
- Not proven: that retatrutide or CagriSema is safe outside a trial. Neither is approved yet, so there is no legal way to get them.


# Peptides for weight loss: three approved ones cut 8% to 21%

*Evidence check, October 20, 2026. Updated October 27, 2026.*

> **The claim:** "Approved peptides like Ozempic cut body weight 8% to 21% in large trials."
>
> **Our grade: Solid.** Three peptides are FDA-approved for weight loss in the US, and each cut weight in large randomized trials: liraglutide by 8%, semaglutide by 15% to 19%, tirzepatide by 21%. The ones sold online as "research" vials are a different story.

![Three weight-loss pens standing like bars in a chart under the words These 3 work: tirzepatide -21%, semaglutide -15%, liraglutide -8%](https://sciencebased.news/images/weight-loss-peptides-hero.jpg)

Jen is 44. Her sister lost 30 pounds on Ozempic, a coworker is on something called Zepbound, and a guy at her gym says "reta" works better than both and sells it in a vial.

Which of these is real medicine, and which one should she ask about?

Five brand names and one nickname cover just three tested drugs, and only some of them are legal to buy. Here is the map, then the trials.


## Where the claim came from

On September 28, 2026, Jeff Nippard, a coach with a degree in biochemistry, posted "Peptides Are Insane" [1]. His opening: "people can simply take a peptide like Ozempic and fat seems to melt off." He sorted peptides into three groups: fat loss, injury healing and anti-aging. He said the fat-loss group is the one backed by big trials, and named three drugs in it: semaglutide, tirzepatide and retatrutide.

He also flagged the problem this article is about. Because these drugs need a prescription, "swaths of people are buying them from black market and gray market sources online, where there's often zero quality control" [1].

A peptide is a short chain of amino acids, the building blocks of protein. The weight-loss peptides copy gut hormones that tell your brain you are full. They are injected because stomach acid breaks them down, though one now comes as a pill.

## What the studies found

### One drug, two names

Most of the confusion comes from drug makers selling the same drug under two names, one for diabetes and one for weight loss.

| You hear | The drug | Made by | FDA status |
|---|---|---|---|
| Ozempic | semaglutide | Novo Nordisk | Approved for type 2 diabetes |
| Wegovy (shot, pill, HD) | semaglutide | Novo Nordisk | Approved for weight loss [7, 9] |
| Mounjaro | tirzepatide | Eli Lilly | Approved for type 2 diabetes |
| Zepbound | tirzepatide | Eli Lilly | Approved for weight loss |
| Victoza | liraglutide | Novo Nordisk | Approved for type 2 diabetes |
| Saxenda | liraglutide | Novo Nordisk | Approved for weight loss |
| Foundayo | orforglipron (a pill, not a peptide) | Eli Lilly | Approved for weight loss [11] |
| CagriSema | cagrilintide + semaglutide | Novo Nordisk | Under FDA review; decision expected late 2026 [17, 18] |
| "Reta" | retatrutide | Eli Lilly | Experimental; Lilly plans to file in early 2027 [15] |

So Ozempic and Wegovy are the same medicine. So are Mounjaro and Zepbound. A doctor can prescribe Ozempic or Mounjaro for weight, but the weight-loss versions are the ones tested and dosed for it. One more peptide, setmelanotide (Imcivree), is approved only for a few rare genetic and brain-injury causes of obesity [22].

### How much each one took off

Here is what the three approved peptides did in their main trials, at the top dose, for someone who starts at 100 kg.


| Generic name | Brand names | Weight lost | After, from 100 kg | Trial length |
|---|---|---|---|---|
| Tirzepatide (weekly shot) | Zepbound; Mounjaro for diabetes | 20.9% (20.9 kg off) | 79.1 kg | 72 weeks (about 17 months) |
| Semaglutide (weekly shot) | Wegovy; Ozempic for diabetes | 14.9% (14.9 kg off) | 85.1 kg | 68 weeks (about 16 months) |
| Liraglutide (daily shot) | Saxenda; Victoza for diabetes | 8.0% (8.0 kg off) | 92.0 kg | 56 weeks (about 13 months) |
| *Placebo (a dummy shot)* | none | 2.4% to 3.1% | about 97 kg | 56 to 72 weeks |

*The average for everyone who started each trial [4, 5, 6]. Some people lost much more, some much less. The higher dose, Wegovy HD, took off 18.7%: 81.3 kg [7].*


![Animation still: average weight from 100 kg in each drug's main trial at the top dose. Placebo about 97 kg after 72 weeks, Saxenda 92.0 kg (−8.0%) after 56 weeks, Wegovy 85.1 kg (−14.9%) after 68 weeks, Zepbound 79.1 kg (−20.9%) after 72 weeks, and the experimental retatrutide 75.0 kg (−25.0%) after 80 weeks.](https://sciencebased.news/images/weight-loss-peptides-race.jpg)
*Tap to play (36 seconds). The same trials, week by week: each line ends at its trial's real result; the path to it is smoothed.*

Saxenda (liraglutide) is the oldest. In the SCALE trial, 3,731 adults injected it daily or a placebo (a dummy shot) for 56 weeks. They lost 8.0% of body weight, against 2.6% on placebo [6].

Wegovy (semaglutide) is a weekly shot. In STEP 1, 1,961 adults without diabetes took it or a placebo for 68 weeks, double-blind (neither they nor their doctors knew who got what). They lost 14.9%, against 2.4% on placebo [4]. A higher dose, Wegovy HD (7.2 mg), took off 18.7% in 72 weeks in the 1,407-person STEP UP trial, against 15.6% on the usual dose and 3.9% on placebo [7]. The FDA approved it on March 19, 2026 [8]. The Wegovy pill took off 13.6% in 64 weeks in 307 adults, against 2.2% on placebo [10].

Zepbound (tirzepatide) copies two gut hormones instead of one. In SURMOUNT-1, 2,539 adults took it or a placebo for 72 weeks. The top dose took off 20.9%, against 3.1% on placebo [5].

Every number here counts everyone who started, including people who quit. People who stayed on the drug lost more.

These were separate trials in different people, so the gaps between them are estimates. One trial did put two of them head to head.

### Zepbound vs Wegovy: which is better

SURMOUNT-5 randomly assigned 751 adults with obesity and no diabetes to the highest dose they could tolerate of tirzepatide or semaglutide, for 72 weeks [13]. Tirzepatide took off 20.2% of body weight, against 13.7% for semaglutide. Waists shrank by 18.4 cm against 13.0 cm. Everyone knew which drug they got, and Lilly, the maker of tirzepatide, paid for it.

For someone who starts at 220 pounds, that gap is about 14 pounds.

### The experimental ones

Retatrutide, the peptide people half-remember as "reta" or "the one that starts with R", copies three gut hormones. In TRIUMPH-1, 2,339 adults took it or a placebo for 80 weeks [14]. The top dose (12 mg) took off 25.0%, against 3.9% on placebo. That is the most any weight-loss drug has done in a large trial. It is not approved, and Lilly plans to ask the FDA in the first quarter of 2027 [15].

CagriSema adds a second hormone, amylin, to semaglutide. In REDEFINE 1, 3,417 adults lost 20.4% in 68 weeks, against 3.0% on placebo [16]. Stomach and gut side effects hit 79.6%, against 39.9% on placebo. Novo filed for approval in December 2025, and a decision is expected by the end of 2026 [17, 18].

![Bar chart of body weight lost at the top dose in each drug's main trial, counting everyone who started: retatrutide 25.0% (experimental), Zepbound 20.9%, CagriSema 20.4% (under FDA review), Wegovy HD 18.7%, Wegovy 14.9%, Wegovy pill 13.6%, Foundayo 11.2%, Saxenda 8.0% (all approved).](https://sciencebased.news/images/weight-loss-peptides-chart.png)

*Redrawn from the main results of each trial [4, 5, 6, 7, 10, 12, 14, 16]. They were separate trials of 56 to 80 weeks, so small gaps between bars mean little.*

So Jen's gym friend is right that reta took off the most. What he sells is not what the trial tested.

### Peptides besides GLP-1 drugs

A few peptides that are not GLP-1 drugs are sold for fat loss too. Tesamorelin (Egrifta) is FDA-approved, but only for belly fat in people with HIV. In two trials of 806 people, it cut the fat around the organs by about 15% in six months, and the fat came back after stopping; see [tesamorelin](/tesamorelin/). AOD-9604 did no better than a placebo in a 502-person trial; see [AOD-9604](/aod-9604/). Setmelanotide works only for the rare causes named above. For weight loss itself, the drugs that copy GLP-1 are the only peptides with large trials behind them.

### The gray market

There is no weight-loss peptide sold over the counter. Every approved one needs a prescription, and anything sold without one, online or in a vial, is not the drug the trials tested.

The FDA says retatrutide and cagrilintide "have not been found safe and effective for any condition" and cannot legally be compounded (mixed by a pharmacy) [2]. It has sent warning letters to companies selling semaglutide, tirzepatide, retatrutide and similar drugs labeled "for research purposes" or "not for human consumption" [2]. Nobody checks those vials for what is in them or how much.

Compounded copies of semaglutide and tirzepatide are a gray zone. While the drugs were in shortage, pharmacies were allowed to make copies. The FDA declared the tirzepatide shortage over in December 2024 and the semaglutide shortage over in February 2025, and the grace periods for copies ended in 2025 [3]. A pharmacy can still compound one for a patient with a documented medical need, but not a mass copy. By May 31, 2026, the FDA had 990 reports of side effects from compounded semaglutide and more than 730 from compounded tirzepatide, some from dosing mistakes, and says the true count is likely higher [2].

### What happens when you stop

This is the limit that matters most. The drugs work while you take them.

In the STEP 1 extension, 327 people were followed for a year after stopping. Those who had been on semaglutide had lost 17.3% by week 68. A year after stopping, they had regained two-thirds of it, for a net loss of 5.6% [19]. Blood pressure went back to where it started.

SURMOUNT-4 tested it the other way. 670 adults who had lost 20.9% on tirzepatide over 36 weeks were randomly split: keep taking it, or switch to placebo [20]. Over the next year, those who stayed lost another 5.5%. Those who switched regained 14.0%. Of those who stayed, 89.5% kept at least 80% of their loss, against 16.6% of those who stopped.

So back to Jen: the two shots her sister and coworker use are real, approved and tested. The question for her doctor is which one, and whether she is ready to stay on it.

## Our grade

| Claim | Evidence | Grade |
|---|---|---|
| The approved peptides cause large weight loss | 5 randomized, placebo-controlled trials, 307 to 3,731 people, 56 to 72 weeks: 8% to 21% | Solid |
| Zepbound takes off more than Wegovy | 1 randomized open-label trial, 751 people, 72 weeks: 20.2% vs 13.7%; agrees with the separate trials | Promising |
| Retatrutide works best | 1 large randomized trial, 2,339 people, 80 weeks: 25.0%; not approved | Promising |
| The weight stays off after you stop | 2 trials: two-thirds regained after semaglutide; 14% regained after tirzepatide | Debunked |
| "Research" vials are the same as the tested drug | No trial; FDA warning letters | Unproven |
| Overall: peptides like Ozempic make the fat melt off | Approved GLP-1 peptides: large, repeated randomized trials | Solid |

The case for the other side: the drug makers paid for every trial here. The head-to-head trial was run by Lilly, the maker of the winner, and was open-label.

"Melts off" hides the cost. In SCALE, 9.9% quit liraglutide for side effects, against 3.8% on placebo [6]. Nausea, vomiting and diarrhea are common on all of them, and Wegovy HD added burning or tingling skin in some people [8].

The fat comes off with some muscle. Up to about 40% of the weight lost can be lean mass when people don't lift or eat enough protein, as Nippard noted [1]; see [keeping muscle on GLP-1 drugs](/glp1-muscle-loss/).

What would change the grade: retatrutide's approval and a head-to-head trial against tirzepatide, and long-term data on stopping slowly instead of all at once.

## What this means for you

- If you want a weight-loss peptide, the legal, tested ones are semaglutide (Wegovy) and tirzepatide (Zepbound), and liraglutide (Saxenda) if a daily shot suits you. Ask your doctor [4, 5, 6].
- If you want the most weight loss from an approved drug, tirzepatide beat semaglutide head to head, about 20% against 14% [13].
- If needles stop you, there are pills: the Wegovy pill and Foundayo took off 11% to 14% in trials [10, 12]. See [the GLP-1 pills](/glp1-pill/).
- If you have heart disease, ask about semaglutide. In 17,604 people with heart disease it cut heart attacks, strokes and heart deaths from 8.0% to 6.5% [21].
- Plan to stay on it. People who stopped regained most of the loss within a year [19, 20].
- Lift two or three times a week and eat enough protein, about 1.6 g per kg of body weight a day. See our [protein target](/protein-target/).
- Skip vials sold "for research use". Retatrutide is not approved, and what is in those vials is unknown [2]. More on [retatrutide's trial](/retatrutide/) and on the [peptides that aren't the next Ozempic](/peptides/).



## What's next

The FDA is expected to decide on CagriSema by the end of 2026 [18]. Lilly plans to file retatrutide in early 2027 [15], and a trial testing it against tirzepatide is under way. We will update this page when either is approved.

More on this: [the GLP-1 pills](/glp1-pill/), [retatrutide's big trial](/retatrutide/), [keeping muscle on GLP-1 drugs](/glp1-muscle-loss/), [BPC-157 and the other popular peptides](/peptides/) and [every peptide we have graded](/peptide-guide/), including [AOD-9604](/aod-9604/), a "fat-loss peptide" that did no better than placebo.

## Sources

1. Nippard J. Peptides Are Insane. YouTube, September 28, 2026. https://www.youtube.com/watch?v=H6SiAe-VObA
2. US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Content current as of October 1, 2026. Compounding limits, adverse-event reports to May 31, 2026, and warnings about products sold "for research purposes". https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
3. US Food and Drug Administration. FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize. End of the tirzepatide (December 19, 2024) and semaglutide (February 21, 2025) shortages and of the grace periods for copies. https://www.fda.gov/drugs/drug-alerts-and-statements/fda-clarifies-policies-compounders-national-glp-1-supply-begins-stabilize
4. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). *N Engl J Med*, 2021. 1,961 adults, randomized, double-blind, placebo-controlled, 68 weeks. Funded by Novo Nordisk. https://doi.org/10.1056/NEJMoa2032183
5. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). *N Engl J Med*, 2022. 2,539 adults, randomized, double-blind, placebo-controlled, 72 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2206038
6. Pi-Sunyer X, Astrup A, Fujioka K, et al. A randomized, controlled trial of 3.0 mg of liraglutide in weight management (SCALE). *N Engl J Med*, 2015. 3,731 adults, randomized, double-blind, placebo-controlled, 56 weeks. Funded by Novo Nordisk. https://doi.org/10.1056/NEJMoa1411892
7. Wharton S, Freitas P, Hjelmesæth J, et al. Once-weekly semaglutide 7.2 mg in adults with obesity (STEP UP). *Lancet Diabetes Endocrinol*, 2025. 1,407 adults, randomized, double-blind, placebo- and active-controlled, 72 weeks. Funded by Novo Nordisk. https://doi.org/10.1016/S2213-8587(25)00226-8
8. US Food and Drug Administration. FDA approves fourth product under National Priority Voucher program, higher dose semaglutide. Press release, March 19, 2026. https://www.fda.gov/news-events/press-announcements/fda-approves-fourth-product-under-national-priority-voucher-program-higher-dose-semaglutide
9. Novo Nordisk. FDA approves Novo Nordisk's Wegovy pill, the first and only oral GLP-1 for weight loss in adults. Press release, December 22, 2025. https://www.prnewswire.com/news-releases/fda-approves-novo-nordisks-wegovy-pill-the-first-and-only-oral-glp-1-for-weight-loss-in-adults-302648344.html
10. Wharton S, Lingvay I, Bogdanski P, et al. Oral semaglutide at a dose of 25 mg in adults with overweight or obesity (OASIS 4). *N Engl J Med*, 2025. 307 adults, randomized, double-blind, placebo-controlled, 64 weeks. Funded by Novo Nordisk. https://doi.org/10.1056/NEJMoa2500969
11. Eli Lilly. FDA approves Lilly's Foundayo (orforglipron), the only GLP-1 pill for weight loss that can be taken any time of day without food or water restrictions. Press release, April 1, 2026. https://investor.lilly.com/news-releases/news-release-details/fda-approves-lillys-foundayotm-orforglipron-only-glp-1-pill
12. Wharton S, Aronne LJ, Stefanski A, et al. Orforglipron, an oral small-molecule GLP-1 receptor agonist for obesity treatment (ATTAIN-1). *N Engl J Med*, 2025. 3,127 adults without diabetes, randomized, double-blind, placebo-controlled, 72 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2511774
13. Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). *N Engl J Med*, 2025. 751 adults without diabetes, randomized, open-label, 72 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2416394
14. Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). *N Engl J Med*, 2026. 2,339 adults without diabetes, randomized, double-blind, placebo-controlled, 80 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2604169
15. Eli Lilly. Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials. Press release, July 23, 2026. Plan to file with the FDA in the first quarter of 2027. https://www.prnewswire.com/news-releases/lillys-triple-agonist-retatrutide-successful-in-two-additional-phase-3-obesity-trials-delivering-significant-improvements-in-weight-and-a1c-302832674.html
16. Garvey WT, Blüher M, Osorto Contreras CK, et al. Coadministered cagrilintide and semaglutide in adults with overweight or obesity (REDEFINE 1). *N Engl J Med*, 2025. 3,417 adults, randomized, double-blind, placebo- and active-controlled, 68 weeks. Funded by Novo Nordisk. https://doi.org/10.1056/NEJMoa2502081
17. Novo Nordisk. Novo Nordisk files for FDA approval of CagriSema. Press release, December 18, 2025. https://www.novonordisk-us.com/media/press-releases/novo-nordisk-cagrisema-fda-nda-submission.html
18. Novo Nordisk. CagriSema demonstrated 23% weight loss in the open-label head-to-head REDEFINE 4 trial. Company announcement, February 23, 2026. FDA decision expected by late 2026. https://www.novonordisk.com/content/nncorp/global/en/news-and-media/news-and-ir-materials/news-details.html?id=916501
19. Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. *Diabetes Obes Metab*, 2022. 327 adults followed 52 weeks after stopping, exploratory analysis. Funded by Novo Nordisk. https://doi.org/10.1111/dom.14725
20. Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity (SURMOUNT-4). *JAMA*, 2024. 783 adults enrolled, 670 randomized after a 36-week lead-in, double-blind, placebo-controlled withdrawal, 52 weeks. Funded by Eli Lilly. https://doi.org/10.1001/jama.2023.24945
21. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). *N Engl J Med*, 2023. 17,604 adults with heart disease, randomized, double-blind, placebo-controlled, about 40 months. Funded by Novo Nordisk. https://doi.org/10.1056/NEJMoa2307563
22. Rhythm Pharmaceuticals. Imcivree (setmelanotide) injection, prescribing information, revised April 2026. Approved for obesity from acquired hypothalamic obesity, Bardet-Biedl syndrome, and POMC, PCSK1 or LEPR deficiency only. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=70c3ccf7-4df0-4c75-ba07-fede9970c8d9&type=display