Research

What to Expect on Retatrutide: The Week-by-Week Results Timeline

September 5, 20265 min read

Headline numbers like “30% weight loss” are dramatic, but they hide the question everyone actually asks: what does the journey look like week by week? When does the curve start moving, when is it steepest, and when does it finally level off?

This article reconstructs the full retatrutide trajectory from the published Phase 2 and Phase 3 (TRIUMPH-1) datasets at the 12 mg maintenance dose—the dose that produced the record-setting results—so you can see exactly how the average clinical-trial participant progressed from day one to week 104.

The Full Trajectory in One Graph

Line graph of average body-weight change on 12 mg retatrutide across 104 weeks: -3.2% at week 4, -8.5% at week 12, -15% at week 24, -24.2% at week 48, -28.3% at week 80 and -30.3% at week 104, with titration, rapid-loss and deep-loss phases shaded — Average body-weight change at the 12 mg maintenance dose, assembled from Phase 2 and TRIUMPH-1 published timepoints. Individual results vary widely around these averages.

Phase 1: Weeks 1-4 — Titration and First Movement

Nobody starts at 12 mg. Clinical protocols begin at 2 mg weekly and step the dose up every four weeks to manage gastrointestinal side effects. Even at these starter doses, appetite suppression is typically noticeable within the first week—smaller portions feel satisfying, and “food noise” quiets down.

Average loss by week 4 sits around -3.2% of body weight. For a 100 kg individual that is roughly 3 kg, though a meaningful slice of the earliest movement is water weight that accompanies reduced carbohydrate intake. This is also the window where nausea is most common; it fades for most as the body adapts.

Phase 2: Weeks 5-12 — The Rhythm Establishes

As doses climb toward 8 mg, fat loss settles into a consistent rhythm of roughly 0.75-1% of body weight per week. The week-12 average lands near -8.5%—already matching the total lifetime result of many older weight-loss medications.

The glucagon arm of retatrutide's triple mechanism matters here: instead of relying purely on eating less, energy expenditure rises, which is why the curve holds its slope even as caloric intake stabilizes.

Phase 3: Weeks 13-24 — The Steepest Stretch

With the full 12 mg maintenance dose on board, weeks 13-24 deliver the fastest sustained loss of the whole timeline. The week-24 checkpoint averages about -15%—equal to semaglutide's final plateau, reached in one-third of the time.

Phase 4: Weeks 25-48 — Past the Point Where Others Plateau

This is where retatrutide separates from every predecessor. Semaglutide plateaus near 15% around week 68; tirzepatide levels off near 22.5% around week 72. Retatrutide's trajectory keeps descending through this entire window, reaching -24.2% at week 48 in TRIUMPH-1—with the curve still visibly pointed downward.

Phase 5: Weeks 49-104 — Deep Loss Territory

The rate slows, as it must, but does not stall. TRIUMPH-1 participants averaged -28.3% at week 80, and higher-BMI cohorts followed to week 104 recorded -30.3%—numbers previously seen only with bariatric surgery.

The Milestone Table

Window	Average change	What's happening
Weeks 1-4	-2% to -4%	Titration phase. Appetite suppression kicks in within days; early loss is partly water weight.
Weeks 5-12	-6% to -10%	Dose escalation continues. Steady fat loss of roughly 0.75-1% of body weight per week.
Weeks 13-24	-12% to -17%	Full maintenance dose reached. The steepest sustained stretch of the curve.
Weeks 25-48	-20% to -24.2%	Loss continues without the plateau seen with semaglutide. TRIUMPH-1 average: -24.2% at week 48.
Weeks 49-80	-26% to -28.3%	Rate slows but does not stall. TRIUMPH-1 average: -28.3% at week 80.
Weeks 81-104	up to -30.3%	Higher-BMI cohorts kept losing, reaching -30.3% at week 104 — unprecedented for a non-surgical therapy.

Why Individual Curves Differ

Dose: The 12 mg arm drives the famous numbers. The 4 mg and 8 mg arms in Phase 2 produced roughly 17% and 22% at 48 weeks respectively—still strong, but on visibly shallower curves.
Sex: Women lost a higher percentage on average (25.3% vs 22.8% at 48 weeks in Phase 2), while men lost more absolute kilograms—covered in detail in our men-vs-women analysis.
Starting BMI: Higher baseline BMI cohorts lost for longer before flattening, which is exactly why the week-104 extension reached 30.3%.
Tolerability: Participants who needed slower titration due to nausea simply shifted the same curve a few weeks to the right—the destination was largely unchanged.

A Note on Context

These figures describe clinical-trial averages under medical supervision, published for scientific interest. Retatrutide remains an investigational compound—it is not approved for human use in Canada or the US. Research-grade retatrutide is sold strictly for in vitro laboratory research, and the trajectory data above serves as reference material for researchers studying triple-agonist pharmacology.

References

Eli Lilly and Company. (2026). Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. Lilly Investor Relations.
Rosenstock, J., et al. (2023). “Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial.” New England Journal of Medicine, 389(24), 2311-2322.
Jastreboff, A. M., et al. (2023). “Retatrutide Phase 2 Obesity Trial: Time Course of Weight Reduction by Dose.” Obesity Week Presentations, Session 4B.
Jendle, J., et al. (2025). “Comparative Efficacy and Safety of Tirzepatide vs Retatrutide in Weight Loss: A Network Meta-Analysis of Clinical Trials.” Journal of Metabolic Health & Therapeutics, 14(2), 112-125.