Retatrutide

Step	Weeks	Dose	Purpose
Weeks 1–4	—	2 mg	Initial tolerance assessment; GI acclimation
Weeks 5–8	—	4 mg	First escalation; meaningful weight loss begins
Weeks 9–12	—	8 mg	Second escalation; approaching therapeutic range
Week 13+	—	12 mg	Full therapeutic dose; sustained weight loss

Beginner Protocol

Intermediate Protocol

Advanced Protocol

Reconstitution and handling notes

Stacking Notes

Additional Dosage Notes

Retatrutide has a rapidly-accumulating but still incomplete evidence base: strong Phase 2 data in obesity, type 2 diabetes, and MASLD (fatty liver). Phase 3 results began arriving in December 2025, and the program (which also covers knee osteoarthritis and cardiovascular outcomes) is still running.

Pivotal Phase 2 obesity trial: Jastreboff et al., 2023 (NEJM; PMID 37366315)

338 adults with obesity (BMI >=30, or >=27 with a weight-related condition) were randomized to retatrutide 1, 4, 8, or 12 mg weekly (with lower starting doses and stepwise escalation) or placebo for 48 weeks. At the maximum 12 mg dose:

• Mean body weight reduction: 24.2% at 48 weeks (~26 kg from a ~109 kg baseline; placebo ~ -2.1%)
• Responder rates at 12 mg: 100% lost >=5%, 93% lost >=10%, 83% lost >=15%
• Systolic BP fell ~11 mmHg; triglycerides ~30%; HDL rose ~10%
• GI adverse events were the most common, dose-related, mostly mild-to-moderate, and partly mitigated by a lower (2 mg) starting dose

This is the foundational efficacy citation for retatrutide and the basis for the Phase 3 TRIUMPH program.

Phase 2 T2DM trial: Rosenstock et al., 2023 (Lancet; PMID 37385280)

281 adults with type 2 diabetes (managed with diet/exercise alone or stable metformin) were randomized to retatrutide, placebo, or dulaglutide 1.5 mg (active comparator); primary endpoint at 24 weeks, key secondary at 36 weeks. At the maximum retatrutide dose (12 mg weekly):

• HbA1c reduction: -2.02 percentage points at 24 weeks (vs -0.01 for placebo and -1.41 for dulaglutide)
• Mean body weight reduction: ~16.9% at 36 weeks

Retatrutide was significantly superior to the dulaglutide active comparator; cross-trial comparison suggests glycemic efficacy in the range of tirzepatide (no head-to-head exists). These Phase 2 data informed Phase 3 dose selection.

Phase 2a MASLD / fatty-liver substudy: Sanyal et al., 2024 (Nature Medicine; PMID 38858523)

Substudy (n=98) of the obesity trial, in participants with metabolic dysfunction-associated steatotic liver disease and >=10% liver fat. Primary endpoint (mean relative change in liver fat at 24 weeks): -81.4% at 8 mg and -82.4% at 12 mg, versus +0.3% for placebo (all P<0.001 vs placebo). Normal liver fat (<5%) was achieved by 79% (8 mg) and 86% (12 mg) of participants at 24 weeks. These are among the largest hepatic-fat reductions reported for any incretin-class agent, driving interest in a future MASH indication.

Phase 1b pharmacokinetics: Urva et al., 2022 (Lancet; PMID 36354040)

First multiple-ascending-dose study, in people with type 2 diabetes. Established a ~6-day half-life, dose-proportional exposure, and once-weekly dosing feasibility, with dose-dependent reductions in glucose and body weight and a mostly mild-to-moderate GI side-effect profile.

Phase 3 TRIUMPH program (obesity)

• TRIUMPH-1 (obesity without T2DM): 28.3% average weight loss at 80 weeks on 12 mg, and 30.3% at 104 weeks in an extension for participants who started with a BMI of 35 or higher (Eli Lilly topline, May 2026)
• TRIUMPH-2 (obesity + T2DM): met its primary endpoint, 20.8% weight loss at 80 weeks on 12 mg (Eli Lilly topline, July 2026)
• TRIUMPH-3 (severe obesity + established cardiovascular disease): met its primary endpoint, 22.6% weight loss at 80 weeks on 12 mg (Eli Lilly topline, July 2026)
• TRIUMPH-4 (knee osteoarthritis in obesity): 28.7% weight loss at 68 weeks on 12 mg; WOMAC knee pain scores fell 74.3% on 12 mg and 75.8% on 9 mg, versus 40.3% on placebo (Eli Lilly topline, December 2025)

The TRIUMPH obesity results so far are Eli Lilly toplines; the full peer-reviewed papers and long-term cardiovascular outcomes data are still to come. The first Phase 3 results paper, TRANSCEND-T2D-1 (Lancet 2026, PMID 42250575), reported HbA1c reductions of 1.69-1.94% and weight loss of 11.5-15.3% at 40 weeks with retatrutide monotherapy in type 2 diabetes.

What is still missing (as of 2026)

• No peer-reviewed TRIUMPH results yet: the only published Phase 3 results are from TRANSCEND-T2D-1 in type 2 diabetes
• No head-to-head results vs tirzepatide yet: a Phase 3 trial comparing the two in obesity is still running, so comparisons are cross-trial for now
• No definitive cardiovascular outcomes data yet: TRIUMPH-3 reported small, inconclusive counts of major cardiovascular events (Eli Lilly topline, July 2026), and the dedicated outcomes trial, TRIUMPH-Outcomes, is still running
• Long-term weight maintenance: peer-reviewed data cover up to 48 weeks; Eli Lilly's toplines run to 80 weeks (104 weeks in a TRIUMPH-1 extension), and a Phase 3b maintenance trial is still running
• Pregnancy / pediatric safety: no data; contraindicated
• Real-world safety: trial populations only

Off-label 'biohacker' use of retatrutide at 2-12 mg weekly extrapolates from the Phase 2 schedule and has not been validated in the general population.

Retatrutide has a GLP-1-class side-effect profile with additional considerations from its GIP and glucagon receptor components.

Common (>10% of Phase 2 participants)

• Nausea: most frequent adverse event; dose-related; typically worst in first 2-4 weeks of each dose titration step; resolves with continued dosing. Severity: mild-moderate in most; severe in ~10-15% at the 12 mg dose
• Vomiting: dose-related; more frequent than on semaglutide or tirzepatide at equivalent weight-loss rates
• Diarrhea: common across GLP-1 class
• Constipation: less common than nausea but still frequent
• Decreased appetite: this is the therapeutic effect; can be uncomfortable initially and causes some patients to discontinue
• Injection site reactions: mild erythema, pruritus; usually transient
• Dyspepsia / eructation: GLP-1-mediated gastric delay effects

Uncommon (1-10%)

• Heart rate elevation: mean ~6-8 bpm increase; larger than semaglutide or tirzepatide (likely glucagon receptor-mediated). Clinically usually asymptomatic but monitor in patients with baseline cardiac concerns
• Transient fasting hyperglycemia during uptitration: paradoxical elevation of fasting glucose during early dose escalation (glucagon-receptor-mediated hepatic glucose output); usually self-limited as GLP-1/GIP insulin-secretory effect catches up
• Mild hepatic enzyme elevation: ALT/AST modest increases; mechanism unclear; monitor
• Fatigue / lethargy: more common than with semaglutide; likely multifactorial
• Hypoglycemia: rare as monotherapy; can occur when combined with sulfonylureas or insulin (requires dose adjustment of co-therapy)
• Gallbladder events: cholelithiasis, cholecystitis; GLP-1 class effect; no retatrutide-specific signal beyond the class

Rare but important

• Acute pancreatitis: GLP-1 class signal; rare (~<0.5%); stop immediately if suspected and investigate
• Severe gastrointestinal events: gastroparesis, ileus, or gastric retention; rare but consistent with GLP-1 class mechanism
• Thyroid C-cell tumors / MTC: GLP-1 class signal from rodent carcinogenicity studies; absolute contraindication in MEN-2 and personal/family history of MTC
• Diabetic retinopathy progression: seen with rapid glycemic correction in GLP-1 trials; monitor in diabetic patients

Retatrutide-specific considerations (triple-agonist trade-offs)

• Higher GI burden at maximal dose: the 12 mg dose is associated with substantially more nausea/vomiting than semaglutide 2.4 mg or tirzepatide 15 mg. Users should uptitrate slowly and may need to hold at intermediate dose (4-8 mg) if 12 mg is not tolerated
• Heart rate elevation: the most clinically distinctive side effect vs other GLP-1-class drugs; consistent with glucagon receptor pharmacology; discuss with cardiologist if baseline resting HR >90 or any cardiac history
• Transient glycemic variation: the first 4-8 weeks of uptitration may feel metabolically unusual (fasting glucose slightly up even as weight drops); stabilizes at steady state
• Dysesthesia (unpleasant abnormal skin sensations): reported in the Phase 3 trials. It occurred in 12.5% of participants on 12 mg in TRIUMPH-1 and 20.9% on 12 mg in TRIUMPH-4, against 0.9% and 0.7% on placebo, and was generally mild to moderate (Eli Lilly toplines)
• Unknown long-term effects: no peer-reviewed data beyond 48 weeks yet (Eli Lilly's Phase 3 toplines run to 80 weeks, and 104 in one extension); long-term safety is extrapolated from GLP-1 class plus glucagon pharmacology

What users should monitor

• Baseline: HbA1c, fasting glucose, lipid panel, comprehensive metabolic panel, liver function, thyroid, blood pressure, resting heart rate, pregnancy test (women of childbearing age)
• Every 4 weeks during uptitration: fasting glucose, blood pressure, heart rate, subjective GI tolerance
• Every 12 weeks on maintenance: HbA1c, weight, liver function, lipids
• Annually: Full panel + cardiovascular assessment