Weight-loss trials: participants and duration
The cleanest comparison is inside one trial. Separate studies remain useful when their populations and observation periods stay visible.
The same 72-week window
SURMOUNT-5 compared tirzepatide and semaglutide directly in 751 adults with obesity and without type 2 diabetes. At 72 weeks, mean weight change was -20.2% and -13.7%, respectively. This comparison gives both treatments a common study population and observation period.
I start there because it removes some of the guesswork involved in comparing unrelated percentages. It still leaves questions about particular patients, other illnesses and outcomes after the study. The trial establishes a group difference within its own conditions.
Separate obesity studies
| Study | Who was studied | Follow-up | Mean body-weight change |
|---|---|---|---|
| Retatrutide Phase 2 | 338 adults with obesity, or overweight with a comorbidity | 48 weeks | -24.2% in the highest-treatment group; -2.1% placebo |
| Semaglutide STEP 1 | 1,961 adults with overweight or obesity, without diabetes | 68 weeks | -14.9% semaglutide; -2.4% placebo |
| Tirzepatide SURMOUNT-1 | 2,539 adults with obesity, or overweight with a weight-related complication, without diabetes | 72 weeks | -15.0%, -19.5% and -20.9% across tirzepatide groups; -3.1% placebo |
These rows identify distinct experiments. A percentage divided by the number of weeks would suggest a steady pace that the final average cannot establish. I want the intervening visits to describe the shape of change.
Other clocks inside the trials
Retatrutide’s diabetes trial assessed glucose at week 24 and weight at week 36. Its liver-fat substudy measured a substantial reduction at week 24 and followed participants to week 48. The obesity trial recorded a heart-rate increase peaking around week 24. Timing changes which question a result can answer.
Semaglutide’s SELECT cardiovascular trial and FLOW kidney trial counted serious illness in their respective populations. The 40-week tirzepatide diabetes comparison assessed glucose and weight against semaglutide. Their outcomes deserve separate space rather than being converted into a general score for speed.
AOD-9604’s failed obesity programme
The AOD-9604 safety programme included follow-up ranging from seven days to 24 weeks. Its human weight-loss development failed to show the sought benefit, despite positive mouse experiments. That gives it a fundamentally different place in this comparison.
I cannot interpret failed human efficacy as a slower version of the positive results above. The AOD-9604 account follows the animal experiments, tolerability reports and human disappointment separately.
Plateaus and discontinuation
A plateau requires observations showing that weight has settled over a period. A final visit can occur while change continues. What happens after treatment stops requires follow-up after stopping; a trial endpoint alone supplies no answer.
For retatrutide, the development review leaves durability and longer-term outcomes open. Across these compounds, the question of how quickly weight changed and the question of whether a benefit lasts require different observations. Those unanswered intervals defeat my urge to name a fastest peptide.