Retatrutide vs. Semaglutide: What Clinical Research Shows

How each drug works

Semaglutide is a GLP-1 receptor agonist. It mimics the gut hormone GLP-1, which increases insulin when blood sugar is high, lowers glucagon, slows stomach emptying, and reduces appetite through the brain. It is modified so it lasts about a week in the body.

Retatrutide activates the GLP-1 receptor plus two more:

• The GIP receptor, a second gut hormone pathway that also supports insulin release and appears to influence fat tissue.
• The glucagon receptor, which increases energy expenditure and fat burning. On its own glucagon raises blood sugar, so pairing it with GLP-1 and GIP is meant to keep glucose controlled while adding calorie burn.

The practical difference: semaglutide works mainly by reducing how much you eat. Retatrutide is designed to reduce intake and increase energy use at the same time.

Weight loss in trials

In separate trials, average weight loss was about 15% with semaglutide 2.4 mg (STEP-1, 68 weeks) and 25% with retatrutide 12 mg (TRIUMPH-1, 80 weeks). Lilly’s press release also reported 28.3% for TRIUMPH-1 at 12 mg, an estimate of the effect if everyone had stayed on the drug. No trial has compared the two drugs, so these figures can’t show which works better.

Blood sugar and diabetes

Semaglutide is approved for type 2 diabetes as Ozempic (injection) and Rybelsus (tablet). Both drugs lower A1c substantially in trials.

In the published TRIUMPH-2 paper (Lancet, September 29, 2026), retatrutide lowered A1c by 1.4 to 1.6 percentage points at 80 weeks across doses. Its earlier phase 2 trial reported reductions of up to about 2 points at 36 weeks. Without a head-to-head trial, it isn’t known whether one lowers it more than the other; TRANSCEND-T2D-2 is testing this directly.

Heart, kidney, and liver outcomes

This is where semaglutide has a clear lead, simply because it has been studied longer.

• Cardiovascular: In the SELECT trial of 17,604 adults with cardiovascular disease and overweight or obesity but no diabetes, semaglutide 2.4 mg reduced major adverse cardiovascular events by 20% over about 40 months. Wegovy carries an FDA-approved indication for reducing cardiovascular risk.
• Kidney: In FLOW, semaglutide 1 mg reduced kidney disease progression in people with type 2 diabetes and chronic kidney disease. Ozempic carries an FDA-approved indication for that use.
• Liver: Wegovy injection is approved for metabolic dysfunction-associated steatohepatitis (MASH) with moderate to advanced liver fibrosis. That approval is an accelerated approval, which means a confirmatory trial is still required.

Retatrutide’s TRIUMPH-3 trial in adults with cardiovascular disease reported 44 major cardiovascular events on retatrutide versus 52 on placebo, a hazard ratio of 0.82 (95% CI 0.55 to 1.22, not statistically significant). That trial was not designed to prove cardiovascular benefit. A dedicated outcomes trial, TRIUMPH-OUTCOMES, is ongoing.

Side effects

Both cause nausea, diarrhea, vomiting, and constipation, mostly during dose escalation. In STEP 1, 4.5% of semaglutide participants stopped because of side effects. In TRIUMPH-1, Lilly’s press release reported that 11.3% on retatrutide 12 mg did.

Retatrutide trials have also reported dysesthesia (abnormal skin sensations) in up to about 21% of participants at 12 mg. In the phase 2 trial, heart rate rose with higher doses, peaked around 24 weeks, then declined. Both need more study.

Semaglutide’s label includes a boxed warning about thyroid C-cell tumors in rodents, plus warnings for pancreatitis, gallbladder disease, and other class effects. Retatrutide’s label does not exist yet.

Dosing and devices

Semaglutide for weight management: the label starts at a low dose and raises the dose in steps every 4 weeks; see the semaglutide calculator’s label-dose table for the steps. The Wegovy label also lists a 7.2 mg dose; who it is for is set out in the label. Wegovy comes as single-dose pens and syringes, a four-dose FlexTouch pen, and a once-daily tablet. Ozempic comes as pens and prefilled syringes for diabetes doses up to 2 mg.

Retatrutide trials tested 4, 9, and 12 mg maintenance doses reached by stepwise increases; this is reported here as trial design, not a schedule for anyone to follow. There is no approved strength, device, or schedule.

Availability

Semaglutide is prescription-only and dispensed by licensed pharmacies. Retatrutide is available only in clinical trials. The FDA has said retatrutide cannot be used in compounding, and “research use only” products sold online are unapproved drugs of unknown quality. Lilly plans to file for FDA approval in the first quarter of 2027.