Retatrutide Clinical Trial Doses and Escalation Schedule

The Phase 2 clinical trial for retatrutide evaluated five dose levels administered as weekly subcutaneous injections: 1 mg, 2 mg, 4 mg, 8 mg, and 12 mg. Participants were randomly assigned to one of these dose groups or a placebo group, and treatment continued for 48 weeks.

The trial enrolled adults with obesity (BMI of 30 or greater) or overweight (BMI of 27 or greater) with at least one weight-related comorbidity. This is the same general eligibility criteria used in pivotal trials for semaglutide and tirzepatide, allowing for rough comparisons between the medications.

Participants in the higher-dose groups did not start at their target dose. Instead, the trial used a gradual escalation protocol to reduce gastrointestinal side effects, similar to the approach used with semaglutide and tirzepatide.

For the 8 mg and 12 mg groups, the escalation followed this general pattern:

Weeks 1-4: starting dose (typically 2 mg) Weeks 5-8: intermediate dose increase Weeks 9-12: further dose increase Weeks 13+: target maintenance dose

The exact escalation steps varied by dose group. Participants in the 1 mg and 2 mg groups started at their target dose without escalation. The 4 mg group had a brief ramp-up period. This design mirrors real-world clinical practice where gradual dose increases help the body adjust to GLP-1-class medications and improve long-term tolerability.

The results demonstrated a clear dose-response relationship. Higher doses produced greater weight loss, with all active-treatment groups significantly outperforming placebo:

1 mg: approximately 8% body weight loss at 48 weeks 2 mg: approximately 13% body weight loss 4 mg: approximately 17% body weight loss 8 mg: approximately 22% body weight loss 12 mg: approximately 24.2% body weight loss Placebo: approximately 2% body weight loss

The 12 mg result -- 24.2% average body weight loss -- represents the highest mean weight loss ever observed in a randomized pharmaceutical trial. Even the 4 mg dose (17%) exceeded the weight loss typically seen with semaglutide 2.4 mg in the STEP trials.

Gastrointestinal side effects were the most commonly reported adverse events and were dose-dependent. The most frequent were nausea, diarrhea, vomiting, and decreased appetite. These side effects were generally mild to moderate in severity and most common during the dose escalation phase.

Participants in the 12 mg group reported higher rates of GI side effects compared to the 1 mg group, which is consistent with the dose-dependent pattern seen across all GLP-1-class medications. Notably, the side effect profile was qualitatively similar to semaglutide and tirzepatide -- no novel or unexpected adverse events emerged from the triple-agonist mechanism.

The Phase 3 program will include larger, longer trials with more diverse patient populations. These trials are expected to test the higher doses (likely 8 mg and 12 mg) that showed the most impressive results in Phase 2, along with potentially refined escalation schedules.

Phase 3 trials will also evaluate retatrutide in specific populations such as patients with type 2 diabetes, cardiovascular disease, and non-alcoholic steatohepatitis (NASH). These broader studies are required by the FDA before a New Drug Application can be submitted. Results from Phase 3 will determine whether the Phase 2 weight loss numbers hold up in larger populations and over longer treatment periods.