Retatrutide Results in the Clinical Trials

What the results pages covers — plain English first

This page reports the numerical results from the retatrutide Phase 2 clinical trials — what actually happened in the studies, broken down by dose arm. Retatrutide is an investigational drug (not yet approved anywhere), developed by Eli Lilly. 'Phase 2 trial' means a study in human participants designed to test whether a drug works and at what dose, before the larger Phase 3 trials that precede a regulatory approval submission. The numbers here are real, peer-reviewed study results. They tell us what happened to specific groups of participants under specific trial conditions — not what will happen to any given individual. The retatrutide results at the headline dose (12 mg once weekly) were striking: a mean 24.2% body-weight reduction over 48 weeks, a three-receptor mechanism producing larger weight reductions than were seen with earlier single- or dual-receptor drugs in equivalent Phase 2 timelines. The body-composition split — how much of that loss was fat versus lean mass — is covered in the section below.

Retatrutide results — Phase 2 obesity trial, by dose arm

Trial: 48-week Phase 2 randomized controlled trial. N = 338 adults with obesity or overweight with comorbidity. Doses: 1, 4, 8, 12 mg once weekly subcutaneous versus placebo. Primary endpoint: mean % body-weight change at 48 weeks ^[1].

| Dose arm | Mean body-weight change at 48 wks | |---|---| | Placebo | -2.1% | | 1 mg | Not reported separately at 48 wks | | 4 mg | Meaningful reduction below placebo | | 8 mg | Dose-dependent, substantial | | 12 mg | -24.2% |

Note: 63% of participants at higher doses achieved ≥20% total body-weight loss, per the 2026 CKM review ^[11]. Systolic blood pressure fell by an average of 8.79 mmHg ^[11]. Urine albumin-to-creatinine ratio (a marker of kidney protein leakage) was significantly attenuated ^[11].

Adverse events: nausea up to 45% at 12 mg (principal GI event); dose-dependent heart-rate increase (approximately +5-7 bpm at 12 mg, peaking at week 24); 18% discontinuation rate at 12 mg, primarily GI-driven; injection-site reactions in approximately 8% of participants.

Phase 2 type 2 diabetes trial results

Trial: 36-week Phase 2 randomized double-blind trial. N = 281 adults with type 2 diabetes (HbA1c 7.0-10.5%). Dose escalation from 0.5 to 12 mg once weekly. Active comparator arm included. Key outcomes ^[2]:

• HbA1c (three-month blood-sugar average) at 24 weeks: -2.02% (12 mg) vs -0.01% (placebo).
• Body weight at 36 weeks: -16.94% (12 mg) vs -3.00% (placebo).
• GI adverse events (nausea, diarrhea, vomiting, constipation) in approximately 35% of participants.
• No severe hypoglycemia; no deaths.
• Background insulin dose-reduction required for participants on insulin.

The T2D trial's shorter endpoint (36 vs 48 weeks for the obesity trial) means direct comparison of the -16.94% vs -24.2% figures is confounded by duration, not solely by the population difference.

MASLD substudy results — liver fat

A substudy within the 48-week Phase 2 obesity trial enrolled 98 participants with MASLD (metabolic dysfunction-associated steatotic liver disease — excess fat stored in the liver, as measured by MRI-PDFF, or magnetic resonance imaging proton density fat fraction) and at least 10% liver fat at baseline ^[5].

Liver-fat change at 24 weeks:

• Placebo: +0.3%
• 1 mg: -42.9%
• 4 mg: -57.0%
• 8 mg: -81.4%
• 12 mg: -82.4%

86% of participants in the 12 mg arm reached normal liver fat content (<5%) at 24 weeks. These reductions were sustained at 48 weeks (-86.0% at 12 mg).

Body-composition results — fat versus lean mass

The 2025 Lancet Diabetes & Endocrinology body-composition substudy used DXA (dual-energy X-ray absorptiometry — an imaging technique that precisely measures fat mass and lean mass) in a subset of the Phase 2 type 2 diabetes trial ^[7]. Findings: dose-dependent reductions in total fat mass, with expected proportional change in lean mass during retatrutide-induced weight loss.

Key context: absolute lean-mass reduction was confirmed. The fat-to-lean loss ratio was more favorable than historic bariatric surgery benchmarks, but for individuals with lower muscle reserve (older adults, those with sarcopenia), absolute lean loss is clinically meaningful. Higher dietary protein has been shown in preclinical models to defend lean mass during pharmacologic weight reduction without compromising fat loss or metabolic benefits ^[8].

Community discussion of retatrutide results on this axis is extensive — resistance training and protein intake are the most consistently cited protective practices. Those reports are anecdotal, not trial data; they appear on the effects page with that label.

What the retatrutide results do and do not tell us

Phase 2 results establish proof of concept and dose-response — they are the basis for proceeding to Phase 3. They do not establish long-term durability. Related GLP-1-class agent data indicate substantial weight regain after discontinuation ^[14]; whether retatrutide's triple-agonist mechanism produces more durable weight loss off-treatment is an open Phase 3 question. The TRIUMPH program cardiovascular outcomes trial (NCT06383390), chronic kidney disease trial (TRANSCEND-CKD), and active-comparator versus tirzepatide trial are all ongoing as of mid-2026. No approved indication exists. These results are what was measured under clinical trial conditions; extrapolation to any individual case is not warranted.