Retatrutide Weight Loss Timeline: Week by Week and Month by Month

Most of the weight comes off in the first 6 months, and it keeps coming off more slowly after that. That's the retatrutide weight loss timeline the trials show: in Lilly's Phase 2 trial, people on 12 mg had lost 17.5% of their body weight on average at 24 weeks and 24.2% at 48 weeks, and in the Phase 3 TRIUMPH-1 trial the 12 mg average reached 28.3% at 80 weeks. The first month is the slow part, because every Phase 3 trial started people at 2 mg.

Search for a week-by-week retatrutide chart and you'll find plenty of precise-looking numbers for week 2, week 6 and week 10. Almost none of them come from a trial. Below are the time points that have actually been measured, and what they mean when your own scale tells a different story. As of September 2026, retatrutide is still in Phase 3 trials and no approved version exists yet; Lilly plans to submit a Biologics License Application (BLA) to the FDA in the first quarter of 2027.

The retatrutide weight loss timeline in measured numbers

Here's every published time point we could find where retatrutide weight loss was measured. Different trials enrolled different people, so read down the last column with care.

Notice the gap between week 12 and week 24. Nobody has published a tabulated week 4, week 8 or week 12 weight for retatrutide in obesity. The Phase 2 registry entry on ClinicalTrials.gov lists body weight only at weeks 24 and 48. So when a chart tells you people lose 4% by week 8, ask where that came from.

To put the percentages in pounds: on a 250 lb start, 17.5% is about 44 lb and 24.2% is about 60 lb. TRIUMPH-1 did this math for its own group, whose average starting weight was 248.5 lb: the 12 mg average at 80 weeks was 70.3 lb. The weight loss calculator runs the same numbers for your starting weight.

How long does reta take to kick in after an injection?

We couldn't find a published time to peak blood level for retatrutide after a shot. What has been published is the half-life: about 6 days, from the Phase 1b trial in The Lancet. That's long enough for once-a-week dosing, and it means each injection is still working on day 6 and 7.

The closest class evidence comes from tirzepatide, Lilly's two-receptor drug. The Zepbound label puts its peak level a median of 24 hours after the injection (range 8 to 72 hours) and says steady levels build up after 4 weeks of weekly shots. That's tirzepatide data, not retatrutide.

Our read: if retatrutide behaves like tirzepatide, a smaller appetite in the first day or two after a shot is plausible, while the full effect of any one dose takes several weeks to build. That fits the way the trials held each dose for 4 weeks before the next step.

The trials counted a smaller appetite as a side effect but didn't say when it started. In TRIUMPH-4, decreased appetite was reported by 19.0% of people on 9 mg and 18.2% on 12 mg, against 9.4% on placebo.

Weeks 1 to 16 follow the dose ladder

The early weeks are slow on purpose. In every TRIUMPH trial, people started at 2 mg once a week and stepped up every 4 weeks until they reached their target dose. The ladder, per Lilly's TRIUMPH-1 release:

People aiming for 4 mg stayed there from week 5 on, and people aiming for 9 mg stayed there from week 13. So "how much reta per week" depends on the week. Someone aiming for 12 mg spends the first month at a sixth of that dose, and only reaches it at week 17. The Phase 2 trial used a slightly different ladder (2, 4, 8 and then 12 mg), with all dose increases finished by week 12, according to its ClinicalTrials.gov record. Our dosage guide covers the doses in more detail; decisions about your own dose belong with a doctor.

What does that mean for week 2 or month 1? No trial has put a number on it. The earliest measured point is the Phase 1b trial in The Lancet: people with type 2 diabetes who were stepped up through 3, 6 and 9 mg to 12 mg within the 12 weeks lost 8.96 kg more than placebo, the most of any group. That's a small trial in a different group, but it shows real loss inside the first 3 months.

Scale noise is loudest early. Less food in your gut changes the number from day to day, and the Zepbound label says tirzepatide slows stomach emptying most after the first dose, an effect that fades over time. Weigh at the same time of day and compare weekly averages, not single mornings.

How fast does reta work once you reach your dose?

The fastest stretch is the first 6 months. In the Phase 2 trial, the 12 mg group lost 17.5% by week 24 and 24.2% by week 48. Put another way, about 72% of their 48-week loss had already happened in the first half.

Not everyone lands on the average. Here's how many people in the 12 mg group crossed each line, from the trial's ClinicalTrials.gov results:

That's about 7 in 10 people (70%) past 15% by week 24. Waist size moved in step: the same group's waist shrank by 14.33 cm at 24 weeks and 19.60 cm at 48 weeks, which is about 5.6 and 7.7 inches. For what that looks like on real bodies, see before and after results.

In the NEJM paper the 8 mg and 12 mg groups were almost level at week 24 (17.3% and 17.5%), and the top dose had pulled only 1.4 points ahead by week 48.

Month 12 and beyond

Loss slows but keeps going. After 24.2% at 48 weeks in Phase 2, the 12 mg averages were 28.7% at 68 weeks in TRIUMPH-4 and 28.3% at 80 weeks in TRIUMPH-1. Those are different trials with different people, so the line between them isn't a single curve.

The clearest look at year 2 is the TRIUMPH-1 extension. Its 532 people had a BMI of 35 or more and had finished 80 weeks on their assigned dose without stopping or cutting it. They then spent 24 more weeks with the dose raised to the most they could tolerate, 9 or 12 mg, and those first assigned 12 mg averaged 30.3% at 104 weeks. It's a selected group of people who tolerated the drug, so the number flatters the typical case a little.

Our read: if you're past month 6 and losing more slowly, you're following the trial pattern. A long, flat stretch with no change at all is a different thing, and our page on the retatrutide plateau covers what the trials and user reports say about it.

Why your timeline won't match the trial average exactly

The trial averages come from screened adults on a known dose, seen at regular trial visits. Several things can push your timeline off them.

The target dose changes the whole curve. At 80 weeks in TRIUMPH-1, 4 mg averaged 19.0%, 9 mg averaged 25.9% and 12 mg averaged 28.3%.

Type 2 diabetes slows it. In TRIUMPH-2, adults with obesity and type 2 diabetes lost 20.8% on 12 mg at 80 weeks, against 28.3% in TRIUMPH-1 without diabetes. Different trials, but the gap is large, and tirzepatide shows the same pattern: on the Zepbound label, 15 mg averaged 20.9% at 72 weeks in people without diabetes and 14.7% in people with it. That's tirzepatide data, not retatrutide.

Then there's how the average is counted. TRIUMPH-1's headline 28.3% assumes everyone stayed on treatment. Counting everyone randomized, including people who stopped, the 12 mg average was 25.0%.

Placebo moves too. People on placebo lost 1.6% by week 24 in Phase 2 and 2.2% by week 80 in TRIUMPH-1, so a small part of any early drop would have happened anyway.

And the trials used Lilly's own drug at known doses. Many people posting timelines on Reddit use their own schedules; thread titles mention 3 mg for months or 4 mg every 5 days, which no trial tested. Anything sold online is not Lilly's product, and no regulator checks how much is really in a vial, so an unusually slow timeline can also mean a vial that holds less than its label says. If you're weighing that risk, our page on retatrutide for sale explains what batch test reports can and can't tell you.

Those forums show the full range: a thread about 10 weeks with no results sits next to one reporting 235 lb down to 197 lb in 2 months. Forum posts, not a study, but a fair reminder that the trial average hides a wide spread.

When the timeline is a reason to call a doctor

Side effects have their own timeline. In the Phase 2 trial, stomach side effects were dose-related and mostly mild to moderate, and starting at 2 mg instead of 4 mg partly reduced them. In TRANSCEND-T2D-1, Lilly said nausea, diarrhea and vomiting happened mainly during dose escalation, so the weeks around each step up the ladder are when they're most likely to come back. The Phase 2 trial also found that heart rate rose with dose, peaked at week 24 and then fell. Our side effects guide covers each one.

Losing weight much faster than the trial averages isn't a win to chase either. The Phase 2 12 mg group's 17.5% over the first 24 weeks works out to about 0.7% of body weight a week. If you're losing well beyond that, eating very little or feeling faint, tell your doctor, and bring a log of your weekly weights and doses so the conversation starts with numbers.