Retatrutide vs Tirzepatide: Weight Loss, Side Effects, and FDA Status

Both are once-weekly injectable compounds that mimic gut hormones controlling appetite and blood sugar.

Tirzepatide is a dual agonist. It activates GLP-1 and GIP receptors, which reduce appetite and improve blood sugar control.

Retatrutide is a triple agonist. It hits the same two receptors and adds the glucagon receptor, which is thought to increase energy expenditure and fat burning. In short, tirzepatide helps you eat less; retatrutide aims to help you eat less and burn more.

These results come from separate trials, not a head-to-head study, so comparisons are approximate.

Tirzepatide: In SURMOUNT-1, adults on the 15 mg dose lost an average of 20.9% of their body weight at 72 weeks. In SURMOUNT-5, tirzepatide outperformed semaglutide (Wegovy), 20.2% vs 13.7%.

Retatrutide: In the Phase 3 TRIUMPH-1 trial, participants on 12 mg lost an average of 28.3% (about 70 pounds) over 80 weeks, and nearly half lost at least 30%. Among people with a BMI of 35 or higher, weight loss reached 30.3% at 104 weeks. Even the lowest 4 mg dose produced close to 20% weight loss.

Based on current data, retatrutide produces roughly 7 to 9 percentage points more weight loss than tirzepatide, approaching results seen with bariatric surgery.

Both compounds share common GI side effects, especially during dose increases: nausea, diarrhea, constipation, and vomiting.

Retatrutide differs in two ways:

• Dysesthesia: About 12% of people on higher retatrutide doses reported tingling, burning, or pins-and-needles skin sensations, compared with under 1% on placebo. It was usually mild and often resolved.
• Higher dropout at top dose: 11.3% of people on 12 mg stopped due to side effects in TRIUMPH-1, versus 4.9% on placebo.

Tirzepatide’s advantage is a well-established safety record from years of use by millions of people. Retatrutide’s long-term safety is still unknown.

Tirzepatide is FDA-approved as Mounjaro for type 2 diabetes and as Zepbound for weight management and obstructive sleep apnea.

Retatrutide is not approved. Lilly plans to file with the FDA in early 2027, which points to possible approval in late 2027 or 2028. Any “retatrutide” sold online today is not a legitimate product and isn’t tested for purity or safety.

Retatrutide leads on weight loss. Tirzepatide leads on certainty: it’s approved, available, and backed by years of safety data. For now, tirzepatide is the only one a doctor can prescribe.

• Is retatrutide stronger than tirzepatide? In trials, yes: about 28% average weight loss versus about 21%. They haven’t been compared head-to-head.
• Is retatrutide the same as Zepbound or Mounjaro? No. Those are brand names for tirzepatide. Retatrutide is a separate compound.
• When will retatrutide be available? Likely late 2027 or 2028, if the FDA approves it.

• Eli Lilly – Retatrutide TRIUMPH-1 Phase 3 topline results
• Endocrine Society – Retatrutide Phase 3 safety data
• The Pharmaceutical Journal – Phase III retatrutide study demonstrates 30% weight loss
• Drugs.com – Retatrutide FDA Approval Status
• American College of Cardiology – SURMOUNT-1 trial summary
• Weill Cornell Medicine – SURMOUNT-5 head-to-head trial