Retatrutide vs. semaglutide: how the two compare

Semaglutide is a pure GLP-1 receptor agonist. It mimics the natural gut hormone GLP-1, which suppresses appetite, slows gastric emptying, and amplifies the insulin response to food.

Retatrutide does all of those things — it activates the GLP-1 receptor too — but it also activates the GIP receptor (which modulates insulin response and fat metabolism) and the glucagon receptor (which appears to increase resting energy expenditure). The combination shifts both sides of the energy balance.

In the Phase 2 obesity trial, participants on the highest 12 mg dose of retatrutide lost an average of 24.2% of body weight at 48 weeks. [1]

In the Phase 3 STEP 1 trial, participants on the 2.4 mg once-weekly dose of semaglutide lost an average of 14.9% of body weight at 68 weeks, vs. 2.4% on placebo. [2]

The numbers are not directly comparable. STEP 1 ran longer (68 weeks vs. 48), enrolled a different population, and used a different dose-escalation schedule. The retatrutide trial was also Phase 2 — Phase 3 readouts may regress somewhat. Even accounting for those caveats, the magnitude advantage in the published literature is consistent.

The most frequently reported side effects in both programs were gastrointestinal: nausea, diarrhea, vomiting, and constipation. These were mostly mild-to-moderate, concentrated during titration, and largely resolved at maintenance dose.

Retatrutide's third receptor target — glucagon — appears to drive a small, dose-dependent increase in resting heart rate of typically a few beats per minute at the highest doses. This is not characteristic of semaglutide. Whether the heart-rate signal has long-term clinical significance is being evaluated in the TRIUMPH-3 trial. [1]

Semaglutide for obesity (Wegovy) titrates 0.25 → 0.5 → 1 → 1.7 → 2.4 mg once weekly with monthly steps. Retatrutide (Phase 2) titrated 2 → 4 → up to 12 mg with four-week steps to maintenance doses of 1, 4, 8, or 12 mg.

The mg numbers are not comparable across molecules — they reflect each drug's receptor potency profile, not its molecular mass.

Semaglutide has been on the US market since 2017. It is available as Ozempic for type 2 diabetes (FDA-approved 2017), Wegovy for chronic weight management (FDA-approved 2021), and Rybelsus as a daily oral form for T2D. Compounded semaglutide is also available through certain telehealth and compounding pharmacy channels.

Retatrutide is not approved by any regulator anywhere. Lilly has not yet filed an NDA. The earliest plausible US approval window, by analyst estimates, is late 2026 through 2027.

Products marketed online as "research retatrutide" are unregulated and not the same molecule being studied in trials. Compounded semaglutide is a different situation — still not FDA-approved as a specific finished product, but compounded under specific regulatory frameworks. Speak with a licensed clinician about any treatment decision.

Wegovy's US list price is approximately $1,350 per month; Novo Nordisk has periodically expanded patient-assistance and direct-to-consumer pricing. Insurance coverage for chronic-weight management indications is uneven across US payers.

Industry analysts generally expect Lilly to price retatrutide at a premium to Zepbound, given its larger trial weight loss. Working assumption: list price ~$1,200 – $1,400 per month, with direct-to-consumer self-pay roughly 30–40% below list. The real numbers will only be clear at launch.

Semaglutide is the most studied, longest-tenured drug in this class. Real-world data, durability across multiple trial programs, and broad availability make it a reasonable first-line choice for many patients.

Retatrutide's trial numbers are larger but come from fewer, shorter trials. Patients who haven't responded optimally to semaglutide, or who need a higher target weight loss, are the most likely candidates for switching once retatrutide is approved.

All treatment decisions belong with a licensed clinician. This page is informational and is not medical advice.