Weight Loss & Metabolic
Best Peptides for Weight Loss: Clinical Evidence, Efficacy & Safety
The honest, evidence-first ranking of peptides for weight loss — the GLP-1-based incretin agonists that work in human RCTs, and the 'fat-burning' GH-fragment peptides that failed in human trials.
weight-loss peptidesGLP-1 agonistsincretin agonistshuman RCT evidenceGH-fragment peptides
The quick verdict
Weight loss is the rare corner of peptide science with genuine human RCT evidence — but only for the GLP-1-based incretin class. Here the agents are ranked by trial strength and magnitude, with a blunt verdict on the 'fat-burning' GH-fragment peptides that failed in humans.
- Best overall
- Tirzepatide (Zepbound / Mounjaro) — The most effective single agent yet FDA-approved for weight — up to ~22.5% mean body-weight loss over 72 weeks in SURMOUNT-1, with 89–96% of participants losing ≥5%.
- Best value
- Semaglutide (Wegovy / Ozempic) — The best-validated peptide, with the deepest evidence base and the only proven hard-outcome benefit — a 20% reduction in major adverse cardiovascular events in SELECT — beyond the scale.
- Best for Maximum weight loss the class can achieve (as trial data, not an available option)
- Retatrutide (LY3437943) — The investigational triple agonist posted the largest weight loss reported for any anti-obesity drug — ~24% at 48 weeks in phase 2 — but remains not FDA-approved and trial-only.
How we evaluated
Agents were ranked by the strength, maturity, and magnitude of their human weight-loss evidence, not by hype or marketing. Every entry that ranks well is supported by completed human randomized controlled trials; we separated FDA-approved from investigational, reported weight loss strictly as seen in the trials, and were explicit where an agent is unapproved or where its best human data are negative. The GH-fragment 'fat-burning' peptides are included precisely to grade them honestly against their human trial record. This is informational and editorial content — not medical advice and not a sourcing guide.
- Evidence strength & maturity. Completed phase 3 RCTs and FDA approval outrank phase 2; positive human trials outrank preclinical or anecdotal data.
- Magnitude of weight loss. Mean percentage body-weight reduction over the trial duration, reported strictly as seen in the published trials.
- Mechanistic rationale. How the agent engages GLP-1, GIP, glucagon, and/or amylin signaling — and, for GH fragments, whether the lipolytic theory translated to humans.
- Regulatory & access reality. FDA approval status, compounding eligibility, and WADA standing — strong evidence does not equal legal availability.
- Honest safety & limitations. GI events, boxed warnings, lean-mass loss, weight regain on cessation, and negative human trials are reported even when they weaken the case.
Rating scale: 1–5 stars reflecting combined evidence strength, weight-loss magnitude, and regulatory maturity for weight loss specifically. Not a safety or recommendation score.
Last verified .
At a glance
| # | Name | Evidence | Rating | Best for | Pricing |
|---|---|---|---|---|---|
| 1 | Tirzepatide (Mounjaro / Zepbound) | A | 5.0 | The largest weight loss available from an FDA-approved, legally prescribable peptide | Brand list price commonly >$1,000/month; varies by coverage |
| 2 | Semaglutide (Wegovy / Ozempic) | A | 5.0 | The best-validated choice — and the only option with proven cardiovascular protection beyond weight | Brand list price commonly >$1,000/month; varies by coverage |
| 3 | Retatrutide (LY3437943) | A | 4.5 | Understanding the maximum weight loss the incretin class can achieve — strictly as trial data, not an available option | No legal retail price (trial-only) |
| 4 | CagriSema (cagrilintide + semaglutide) | A | 4.5 | Following the amylin-plus-GLP-1 combination approach with the deepest investigational phase 3 dataset | No legal retail price (not yet approved) |
| 5 | Survodutide (BI 456906) | A | 4.0 | Tracking the GLP-1/glucagon dual-agonist approach — solid but not class-leading, strictly as trial data | No legal retail price (trial-only) |
| 6 | Liraglutide (Saxenda / Victoza) | A | 3.5 | An approved, legal GLP-1 where a clinician has a specific reason to prefer daily liraglutide | Brand list price; varies by coverage |
| 7 | AOD-9604 | D | 1.5 | Understanding why a heavily marketed GH-fragment 'fat burner' failed the human evidence test | No legal weight-loss product |
| 8 | Fragment 176-191 (hGH frag 176-191) | D | 1.0 | Seeing why the raw GH-fragment theory has never been validated for human weight loss | No legal weight-loss product |
Tirzepatide (Mounjaro / Zepbound)
The most effective single agent yet approved
Tirzepatide is a once-weekly subcutaneous dual GIP/GLP-1 receptor agonist and the most effective single anti-obesity agent yet FDA-approved. Adding GIP agonism to the GLP-1 backbone produces larger weight loss than GLP-1 alone, plausibly via complementary effects on energy intake and adipose and insulin handling. The pivotal evidence is genuine Grade A: in SURMOUNT-1 (N=2,539 adults with obesity and no diabetes, 72 weeks), once-weekly tirzepatide produced mean weight reductions of 16.0% at 5 mg, 21.4% at 10 mg, and 22.5% at 15 mg versus just 2.4% for placebo, with 89 to 96% of participants losing at least 5% of body weight. It is approved as Zepbound for chronic weight management and Mounjaro for type 2 diabetes. Dosing in the label and trials is titrated from 2.5 mg upward in roughly 4-week steps to a 5, 10, or 15 mg maintenance dose to limit gastrointestinal effects. Adverse events are predominantly GI — nausea, diarrhea, vomiting, and constipation, mostly during titration — and it carries the class boxed warning for thyroid C-cell tumors plus pancreatitis and gallbladder cautions.
Strengths
- Largest weight loss of any FDA-approved single agent — up to ~22.5% over 72 weeks in SURMOUNT-1
- Dual GIP/GLP-1 mechanism outperforms pure GLP-1 agonism on weight
- Very high responder rate — 89 to 96% of participants lost at least 5% of body weight
- FDA-approved and legally prescribable (Zepbound for weight, Mounjaro for diabetes)
Weaknesses
- Dose-related GI events (nausea, diarrhea, vomiting, constipation) are the leading cause of discontinuation
- Boxed warning for thyroid C-cell tumors; pancreatitis and gallbladder-disease cautions
- Effect is pharmacological, not curative — weight regain follows discontinuation, as across the class
- Best for
- The largest weight loss available from an FDA-approved, legally prescribable peptide
- Pricing
- Brand list price commonly >$1,000/month; varies by coverage
Semaglutide (Wegovy / Ozempic)
Best-validated — and the only one with proven CV benefit
Semaglutide is a once-weekly subcutaneous GLP-1 receptor agonist and the most thoroughly studied weight-loss peptide. GLP-1 receptor activation slows gastric emptying, enhances glucose-dependent insulin secretion, and acts on hypothalamic and hindbrain appetite circuits to increase satiety and reduce food intake. In the pivotal STEP 1 trial (N=1,961, 68 weeks), once-weekly semaglutide 2.4 mg produced a mean weight loss of 14.9% versus 2.4% for placebo, with 86% of participants losing at least 5%, 69% at least 10%, and 50% at least 15%. Uniquely in the class, semaglutide also carries cardiovascular-outcomes evidence: in SELECT (more than 17,000 adults with established cardiovascular disease and no diabetes), it cut major adverse cardiovascular events by 20% (hazard ratio 0.80), making it the only weight peptide proven to reduce hard cardiovascular endpoints. Dosing is titrated from 0.25 to 2.4 mg over about 16 weeks. GI events are the most common adverse effect — nausea in 44% and diarrhea in 32% in STEP 1 — with about 4.5% discontinuing for GI reasons, and weight regain on cessation is well documented.
Strengths
- Deepest evidence base in the class — multiple large phase 3 RCTs plus a cardiovascular-outcomes trial
- Only weight-loss peptide with proven hard-outcome benefit — 20% MACE reduction in SELECT
- Strong, replicated efficacy — ~14.9% mean loss in STEP 1, with half of participants losing ≥15%
- FDA-approved (Wegovy for weight, Ozempic for diabetes) and legally prescribable
Weaknesses
- GI-predominant adverse events (nausea 44%, diarrhea 32% in STEP 1) drive discontinuations
- Boxed warning for thyroid C-cell tumors; pancreatitis and gallbladder cautions
- Weight regain on cessation is well documented — about two-thirds regained within a year in the STEP 1 extension
- Best for
- The best-validated choice — and the only option with proven cardiovascular protection beyond weight
- Pricing
- Brand list price commonly >$1,000/month; varies by coverage
Retatrutide (LY3437943)
Triple agonist — largest loss reported, but investigational
Retatrutide is an investigational once-weekly subcutaneous 'triple-G' agonist that activates the GLP-1, GIP, and glucagon receptors simultaneously. Adding glucagon-receptor agonism recruits increased energy expenditure and hepatic fat mobilization on top of appetite suppression, and it posted the largest weight loss reported for any anti-obesity drug in its phase 2 trial. In that trial (N=338, 48 weeks), mean reductions were −8.7% at 1 mg, −17.1% at 4 mg, −22.8% at 8 mg, and −24.2% at 12 mg versus −2.1% for placebo, with the weight-loss curve still descending at trial end. A liver-fat substudy showed a roughly 82% relative reduction in hepatic fat at 24 weeks — a striking metabolic signal beyond the scale. Dosing in the trial was subcutaneous once weekly, escalated to a 1 to 12 mg maintenance range. The honest catch is regulatory, not scientific: it is not yet FDA-approved, its phase 3 TRIUMPH program is ongoing, and long-term safety and durability are not established. A transient dose-dependent increase in heart rate was noted and remains under active phase 3 evaluation, alongside the dose-dependent GI events typical of the class. Treat current claims as strong but preliminary.
Strengths
- Largest weight loss reported for any anti-obesity drug — up to −24.2% at 12 mg over 48 weeks in phase 2
- Triple mechanism adds glucagon-driven energy expenditure and ~82% relative liver-fat reduction
- Weight-loss curve had not plateaued at 48 weeks — implying further loss with longer treatment
- Robust phase 2 human RCT evidence (Grade A for the trial)
Weaknesses
- Investigational — not FDA-approved, not compoundable, and only lawfully available inside a registered trial
- Transient dose-dependent heart-rate increase under active phase 3 evaluation; long-term safety unestablished
- Dose-dependent GI events; phase 3 durability and safety database still maturing
- Best for
- Understanding the maximum weight loss the incretin class can achieve — strictly as trial data, not an available option
- Pricing
- No legal retail price (trial-only)
CagriSema (cagrilintide + semaglutide)
Amylin + GLP-1 combination — deep phase 3 data
CagriSema is an investigational fixed-dose combination of cagrilintide, a long-acting amylin analogue, and semaglutide, a GLP-1 agonist — stacking two complementary appetite mechanisms, since amylin agonism suppresses food intake through a distinct hindbrain circuit largely non-overlapping with GLP-1's. Its evidence base is among the deepest in the peptide field. In phase 3 REDEFINE 1 (N=3,417, 68 weeks), CagriSema produced 20.4% mean weight loss, rising to 22.7% with full adherence, versus 14.9% for semaglutide alone, 11.5% for cagrilintide alone, and 3% for placebo — clear additivity over either component. Notably, 60% of CagriSema participants lost at least 20% of body weight and 23% lost at least 30%. Dosing in the trial was once-weekly subcutaneous at a fixed 2.4 mg / 2.4 mg. The honest nuance is that 22.7% fell short of the company's own 25% target — a useful reality check on hype — and cagrilintide as monotherapy has only phase 2 human data, so it grades B on its own. Adverse events were GI-predominant, consistent with the GLP-1 class. It is not yet FDA-approved and, like the other investigational agents, is not legally compoundable.
Strengths
- Deep phase 3 evidence base (N=3,417 in REDEFINE 1) with clear additivity over each component
- Strong magnitude — 22.7% with full adherence, with 60% losing ≥20% and 23% losing ≥30%
- First combination to stack amylin and GLP-1 appetite mechanisms in one weekly injection
- GI-dominant, mostly transient tolerability profile consistent with the class
Weaknesses
- Fell short of the company's own 25% weight-loss target — a check on hype
- Not FDA-approved; not legally compoundable; only lawful exposure is inside a trial
- Cagrilintide alone has only phase 2 data (Grade B), so the amylin arm is less mature than the GLP-1 arm
- Best for
- Following the amylin-plus-GLP-1 combination approach with the deepest investigational phase 3 dataset
- Pricing
- No legal retail price (not yet approved)
Survodutide (BI 456906)
GLP-1/glucagon dual agonist — solid phase 2
Survodutide is an investigational once-weekly GLP-1 and glucagon dual agonist. Like the other glucagon-arm agents, it adds energy expenditure and hepatic fat mobilization to GLP-1's appetite suppression. In a phase 2 dose-finding RCT (46 weeks), the 4.8 mg dose produced −18.7% weight loss versus −2.3% for placebo, a solid result that placed it ahead of semaglutide's roughly 15% but below tirzepatide and retatrutide. It has since advanced to phase 3. Dosing in the trial was once-weekly subcutaneous with a 20-week escalation to 4.8 mg; notably, that rapid escalation drove appreciable GI discontinuations of roughly 25%, a tolerability lesson for the glucagon-arm agents. The overall grade is A for the phase 2 trial but B for the agent as a whole, because it is not approved and its phase 3 program is still ongoing — long-term safety and durability are not yet established. As with all the investigational agents, it is not available through any legal channel outside a registered clinical trial, and any 'research chemical' vials marketed under its name carry none of the trial safety net. Keep expectations measured until phase 3 reports.
Strengths
- Solid phase 2 human RCT — −18.7% at 4.8 mg over 46 weeks, ahead of semaglutide's ~15%
- GLP-1/glucagon dual mechanism adds energy expenditure and hepatic fat mobilization
- Has advanced to phase 3 development, signaling sponsor confidence in the program
- Reported in a peer-reviewed phase 2 RCT (Lancet), not merely press toplines
Weaknesses
- Weight loss (~18.7%) trails tirzepatide, retatrutide, and CagriSema — not class-leading
- Rapid dose escalation drove notable GI discontinuations (~25%) in phase 2
- Investigational — not approved, phase 3 ongoing, long-term safety and durability unestablished
- Best for
- Tracking the GLP-1/glucagon dual-agonist approach — solid but not class-leading, strictly as trial data
- Pricing
- No legal retail price (trial-only)
Liraglutide (Saxenda / Victoza)
First-gen daily GLP-1 — approved but lowest efficacy
Liraglutide is the first-generation, once-daily GLP-1 receptor agonist — the earliest of the approved weight-loss peptides and now generally superseded by the weekly agents. In the SCALE Obesity and Prediabetes trial (N=3,731, 56 weeks), liraglutide 3.0 mg produced a mean weight loss of 8.0% versus 2.6% for placebo, with 63% of participants losing at least 5% and 33% at least 10%. It is FDA-approved as Saxenda for chronic weight management (and as Victoza for type 2 diabetes at lower doses), so its evidence is genuine Grade A. The honest limitation is efficacy and convenience: its effect size is roughly half that of semaglutide and about a third of tirzepatide, and it requires a daily rather than weekly injection, which is why the newer weekly agents have largely superseded it. Its safety profile is GI-predominant, with the same class warnings — the boxed warning for thyroid C-cell tumors and cautions for pancreatitis and gallbladder disease. It remains a legitimate, legal, FDA-approved option, particularly where a clinician has a specific reason to prefer it, but for most people seeking maximum weight loss the weekly agonists are the stronger choice.
Strengths
- FDA-approved (Saxenda) with a large phase 3 RCT behind it (SCALE, N=3,731)
- Genuine Grade A human evidence — 8.0% mean loss, 63% losing at least 5%
- Long real-world track record as the first-generation GLP-1 weight-loss agent
- Legally prescribable, unlike the investigational next-gen agents
Weaknesses
- Lowest efficacy of the approved peptides — roughly half of semaglutide and a third of tirzepatide
- Requires daily injection versus the once-weekly newer agents
- GI-predominant adverse events with the same class warnings (thyroid C-cell, pancreatitis, gallbladder)
- Best for
- An approved, legal GLP-1 where a clinician has a specific reason to prefer daily liraglutide
- Pricing
- Brand list price; varies by coverage
AOD-9604
GH-fragment 'fat burner' — human trial evidence is NEGATIVE
AOD-9604 is a 16-amino-acid modified fragment of human growth hormone (residues 176–191 plus an N-terminal tyrosine), designed around the theory of isolating GH's lipolytic C-terminal region to stimulate fat breakdown without GH's growth or glucose side effects, and heavily marketed for 'fat loss.' The mechanism is real in vitro and in rodents, but it did not translate to clinically meaningful fat loss in adequately powered human trials. Despite an early 12-week phase II signal of roughly 2.8 kg versus 0.8 kg placebo at 1 mg, the pivotal, well-powered phase IIb trial (N=536) failed to show statistically significant weight loss versus placebo, and the developer terminated the program in 2007. Safety across about 900 subjects was reassuring — no IGF-1 elevation and no glucose problems — but efficacy for weight loss was simply not there. It is unapproved by any major regulator and was 'nominated but withdrawn' from FDA 503A Category 2 as of April 2026. Because the best human data are negative, PeptideVox grades it D for weight loss. It is included here not as a recommendation but to grade a widely marketed peptide honestly against its human trial record.
Strengths
- Reassuring safety across ~900 human subjects — no IGF-1 elevation and no glucose problems
- Extensively studied for a wellness peptide — roughly six human trials and an early positive signal
- Mechanistically coherent lipolytic action in vitro and in rodent models
Weaknesses
- Pivotal, well-powered phase IIb trial (N=536) failed to beat placebo on weight loss
- Development terminated in 2007; unapproved by any major regulator
- Best available human evidence is negative — graded D for weight loss
- Best for
- Understanding why a heavily marketed GH-fragment 'fat burner' failed the human evidence test
- Pricing
- No legal weight-loss product
Source: AOD-9604 discontinued-candidate review, Emirati Times 2026
Fragment 176-191 (hGH frag 176-191)
Parent GH sequence — no qualifying human efficacy data
Fragment 176-191 is the unmodified parent growth-hormone sequence underlying AOD-9604, marketed for 'stubborn fat' on the same lipolytic theory. It is lipolytic in vitro and in rodent models, which is the entire basis of its marketing, but it has no positive human weight-loss randomized controlled trial at all — and its modified, more-studied descendant, AOD-9604, already failed in adequately powered humans. That combination is decisive: the preclinical promise did not translate, and the one modified version that was actually tested at scale in humans could not beat placebo. There is therefore no qualifying human efficacy evidence for fragment 176-191 as a weight-loss agent, and PeptideVox grades it D. It is unproven for human weight loss, unapproved by any major regulator, and typically sold only as a 'research chemical / not for human use,' meaning it sits outside any quality, sterility, or legal framework. GH fragments such as this also fall under prohibited peptide-fragment and growth-factor categories in anti-doping, so tested athletes should treat it as banned. It is listed here to close the honest gap between marketing and the human record.
Strengths
- Lipolytic activity demonstrated in vitro and in rodent models
- Simple, well-characterized fragment of a well-understood hormone (human growth hormone)
- Its more-studied modified descendant, AOD-9604, has an extensive human safety record
Weaknesses
- No positive human weight-loss RCT — no qualifying human efficacy data at all
- Its tested descendant (AOD-9604) already failed to beat placebo in humans
- Unapproved, sold only as a 'research chemical,' and in prohibited anti-doping categories — graded D
- Best for
- Seeing why the raw GH-fragment theory has never been validated for human weight loss
- Pricing
- No legal weight-loss product
Frequently asked
What is the single most effective peptide for weight loss right now?
Among FDA-approved options, tirzepatide (Zepbound) produces the largest weight loss — up to about 22.5% mean reduction over 72 weeks in the SURMOUNT-1 trial, with roughly 89 to 96% of participants losing at least 5% of body weight. The investigational triple agonist retatrutide reached about 24% in its phase 2 trial, but it is not yet FDA-approved and its long-term safety and durability are still being established in phase 3. Semaglutide (Wegovy) is the most thoroughly studied and the only weight-loss peptide with proven hard cardiovascular-outcome benefit. So the honest answer depends on what you weigh: tirzepatide for magnitude among approved drugs, semaglutide for depth of evidence and cardiovascular protection.
Do AOD-9604 or 'fragment 176-191' actually cause fat loss?
The best human evidence says no. AOD-9604 is a modified growth-hormone fragment heavily marketed for stubborn fat, but its pivotal, well-powered phase IIb trial (roughly 536 subjects) failed to show statistically significant weight loss versus placebo, and the developer terminated the program in 2007. Across about 900 humans in six trials, safety was reassuring, but efficacy for weight loss simply was not there. Fragment 176-191, the unmodified parent sequence, is lipolytic in test tubes and rodents but has no positive human weight-loss randomized controlled trial at all. PeptideVox grades both D for weight loss. Marketing claims of 'dramatic fat loss' from these peptides are not supported by the human data.
Will I keep the weight off after stopping?
Usually not, without continued treatment or a robust lifestyle program. The effect of these drugs is pharmacological, not curative. In the STEP 1 extension, participants regained roughly two-thirds of their lost weight within a year of stopping semaglutide, and weight regain after discontinuation is the documented pattern for the entire GLP-1 class. These agents manage a chronic condition rather than cure it. From a functional-medicine standpoint, they are best understood as powerful tools that buy metabolic improvement and time, but they work alongside — not instead of — addressing diet quality, sleep, muscle mass, insulin signaling, and the food environment that drive the underlying disease.
Can I still get a cheaper compounded version?
Generally no. The FDA declared the tirzepatide (December 2024) and semaglutide (February 2025) shortages resolved, and the enforcement-discretion window that had let compounding pharmacies make copycat versions has closed. The agency has further proposed not to add semaglutide, tirzepatide, or liraglutide to the 503B bulks list, and it has logged hundreds of adverse-event reports tied to compounded products, including dosing errors requiring hospitalization. The cheap 'compounded GLP-1' era — which had occupied roughly the $100 to $300 range versus over $1,000 a month for brand — is largely over. Unregulated 'research peptide' vials are not a verified-quality or legal substitute for prescribed, FDA-approved product.
Do these drugs do anything beyond weight loss?
Yes, and this is a genuine differentiator for the incretin class. Semaglutide has proven cardiovascular benefit: in the SELECT trial of more than 17,000 adults with established cardiovascular disease and no diabetes, it cut major adverse cardiovascular events by 20% (hazard ratio 0.80), making it the only weight peptide proven to reduce hard cardiovascular endpoints. Retatrutide showed a dramatic roughly 82% relative reduction in liver fat in its phase 2 substudy, and the glucagon-arm agents mobilize hepatic fat. These benefits beyond the scale — cardiovascular and hepatic — are part of why the incretin class has moved from a weight tool to a broader metabolic therapy.
Are the investigational agents like retatrutide and CagriSema available now?
No. Retatrutide, CagriSema, and survodutide have impressive trial numbers but are not FDA-approved as of mid-2026, and their long-term safety and durability are still being established in phase 3. Investigational does not equal available or proven-safe long-term — the only lawful human exposure is inside a registered clinical trial. The approved, legal options for weight loss remain semaglutide, tirzepatide, and liraglutide. Material sold online as a 'research chemical / not for human use' is unapproved, frequently mislabeled or contaminated, and outside any quality, sterility, or legal framework, so the trial efficacy and safety data do not transfer to it. Verify current approval and trial status before relying on any vendor claim.