Retatrutide Results in the Clinical Trials

Before the numbers

Retatrutide results from Phase 1 and Phase 2 trials are some of the largest weight-reduction figures produced by a pharmacological agent in a randomized controlled trial. They are also Phase 2 results in a carefully selected population, administered by clinical investigators, using pharmaceutical-grade product with real-time safety monitoring.

The retatrutide results below are study-design outcomes — what investigators measured in enrolled participants under controlled conditions. They describe what the trials found for those populations, not what any individual would experience. They are not predictions, not guarantees, and not guidance. Phase 3 data will determine whether these results hold in larger, more diverse populations.

Phase 1b results: first-in-human weight and pharmacokinetics

The Phase 1b study (Urva et al., Lancet, 2022) enrolled 72 adults with type 2 diabetes in a 12-week multiple-ascending-dose trial ^[4].

Key retatrutide results: placebo-adjusted weight change at the highest dose -8.96 kg (90% CI: -11.16 to -6.75 kg). Daily blood glucose -2.8 mmol/L at 3 mg. Half-life approximately 6 days. Treatment-emergent adverse events in 63% of participants, predominantly GI and mostly mild to moderate. The Phase 1b established that weekly dosing was pharmacokinetically feasible and that weight loss was dose-dependent — the core findings that justified proceeding to Phase 2.

Phase 2 obesity results: the primary endpoint

The NEJM Phase 2 obesity trial (Jastreboff et al., 2023) is where the headline retatrutide results come from ^[1]. 338 adults with obesity (BMI ≥30 or ≥27 with a weight-related comorbidity; 51.8% men) were randomized to 1, 4, 8, or 12 mg once weekly or placebo over 48 weeks.

Primary endpoint — mean percentage change in body weight at 48 weeks:

• 12 mg: -24.2% (vs -2.1% placebo)
• 8 mg: -17.3%
• 4 mg: -8.7%
• 1 mg: -4.1%

All active doses showed statistically significant separation from placebo. The -24.2% figure at 12 mg represents the largest weight-loss result produced by any drug in a randomized obesity trial at the time of publication ^[6].

Safety outcomes in this trial: GI adverse events were the most common — nausea up to 45% at 12 mg, diarrhea up to 39%, vomiting up to 26%, constipation up to 24%. Discontinuation rate at 12 mg: 18%, primarily GI-driven. Dose-dependent heart-rate increase: mean elevation peaking around 24 weeks, partial attenuation thereafter. Injection-site reactions in approximately 8% of participants.

Phase 2 type 2 diabetes results

The Lancet Phase 2 diabetes trial (Rosenstock et al., 2023) enrolled 281 adults with type 2 diabetes over 36 weeks ^[2].

Retatrutide results at 12 mg:

• HbA1c change at 24 weeks: -2.02% versus -0.01% placebo
• Body weight change at 36 weeks: -16.94% versus -3.00% placebo

No severe hypoglycemia and no deaths in the trial. GI adverse events in 35% of participants. Participants on background insulin required insulin dose reductions during the study — a finding that underscores the interaction risk between retatrutide and existing insulin regimens ^[2].

Phase 2a MASLD substudy results

The Nature Medicine MASLD substudy (Sanyal et al., 2024) enrolled 98 participants with obesity or overweight and metabolic dysfunction-associated steatotic liver disease (MASLD — the current term for fatty liver linked to metabolic risk) having ≥10% liver fat by MRI-PDFF ^[5].

Relative liver-fat change at 24 weeks:

• 12 mg: -82.4% (vs +0.3% placebo)
• 8 mg: -81.4%
• 4 mg: -57.0%
• 1 mg: -42.9%

Participants reaching normal liver fat (below 5%): 86% at 12 mg. Liver-fat reduction sustained to 48 weeks at -86.0% at 12 mg. These are among the largest liver-fat reduction figures measured in a randomized pharmacological intervention trial ^[5].

Phase 3 and head-to-head: results pending

The TRIUMPH Phase 3 program is ongoing. NCT06662383 — the head-to-head Phase 3 trial comparing retatrutide versus tirzepatide — is the most closely watched trial in the retatrutide results pipeline ^[9]. NCT06383390 is the dedicated cardiovascular outcomes trial ^[8]. Neither has published results as of mid-2026.

A cardiology review noted that agents achieving ~24% weight loss (a figure drawn from both retatrutide and tirzepatide trial data) raise the possibility of greater cardiovascular benefit than earlier incretin agents — but explicitly frames this as hypothesis, not established finding, given the absence of long-term outcomes data for retatrutide specifically ^[11]. These are Retatrutide references on the cardiovascular hypothesis page.