Retatrutide Weight Loss Week by Week: The Short Answer
In its clinical trials, people taking the highest dose of retatrutide, 12 mg, lost an average of 17.5% of their body weight by 24 weeks, 24.2% by 48 weeks and about 28% by 68 to 80 weeks. In a two-year extension, those originally on 12 mg reached 30.3%.
These are the figures Lilly and the trial investigators report for people who stayed on treatment as intended. Counting everyone who started, including people who stopped, the 80-week figure in TRIUMPH-1 was 25.0%. Retatrutide is investigational and not approved; for where it stands, see retatrutide's approval status.
Retatrutide Weight Loss Per Week in the Trials
The trials report totals at set points rather than weekly amounts, but the averages give a rough pace. Dividing the Phase 2 results for 12 mg by time, average weight loss worked out to about 0.7% of body weight per week over the first 24 weeks, and about 0.3% per week from week 24 to week 48. For a participant starting at 250 lb, that would be roughly 1.8 lb a week in the first six months and under 1 lb a week in the next six.
These are calculations from group averages, not figures the trials report, and weight does not come off at an even rate: individual results in the trials varied considerably, and the pace slowed over time.
Weeks 1–24: The First Six Months
Treatment in the trials started at a low dose that was increased step by step. Weight loss built steadily through this period: in the Phase 2 trial, published in the New England Journal of Medicine in 2023, people on 12 mg had lost an average of 17.5% of their weight by week 24, compared with 1.6% on placebo.
The Phase 2 trial weighed participants at weeks 1, 4, 8, 12, 16 and 20, but reported exact figures only at weeks 24 and 48; earlier weeks appear only as points on a graph, so percentages quoted online for week 2, week 4 or the first month are estimates. This is also when side effects were most common, while the dose was being increased.
Weeks 25–48: Continued Loss
By week 48, people on 12 mg in Phase 2 had lost an average of 24.2%, compared with 2.1% on placebo. The investigators wrote that weight was still falling when treatment ended and that a plateau had not been reached.
At 48 weeks on 12 mg, 100% of participants had lost at least 5% of their weight, 93% at least 10%, 83% at least 15%, 64% at least 20%, 48% at least 25% and 26% at least 30%.
Weeks 49–68: The First Phase 3 Results
TRIUMPH-4, the first Phase 3 trial with results, announced by Lilly in December 2025, followed 445 adults with obesity and knee osteoarthritis for 68 weeks. Lilly reported average weight loss of 28.7% with 12 mg and 26.4% with 9 mg, compared with 2.1% on placebo.
Weeks 69–80: TRIUMPH-1
TRIUMPH-1 is the largest retatrutide trial reported to date, with 2,339 adults with obesity and without diabetes, followed for 80 weeks and published in the New England Journal of Medicine in September 2026. With 12 mg, weight fell by an average of 28.3%, compared with 2.2% on placebo. The full results by dose are in our TRIUMPH-1 results article.
Lilly reported that 62.5% of people on 12 mg lost at least 25% of their body weight, 45.3% at least 30% and 27.2% at least 35%.
Beyond 80 Weeks: Results at Two Years
About 500 TRIUMPH-1 participants continued for another 24 weeks, on 9 mg or 12 mg depending on the highest dose they tolerated; Lilly described this group as 532 people with a BMI of 35 or more. Those originally assigned to 12 mg had lost an average of 30.3% of their weight at week 104, the longest follow-up reported for retatrutide.
Does Weight Loss Plateau on Retatrutide?
No plateau has been reported so far. In Phase 2, weight was still falling when treatment ended at 48 weeks, and the investigators wrote that a plateau had not yet been reached. In the TRIUMPH-1 extension, people originally on 12 mg reached 30.3% at 104 weeks; that group was a subset of the trial, so the figure is not directly comparable with the 80-week average. When weight loss levels off has not been reported, and no published retatrutide trial has run longer than 104 weeks. What happens after stopping is covered in weight regain after stopping retatrutide.
When Side Effects Are Most Common
In TRIUMPH-1, the most common side effects were gastrointestinal. The paper describes them as mostly transient and mild or moderate, occurring most often while the dose was being increased at the start of treatment.
Over the full 80 weeks on 12 mg, 42.4% of participants reported nausea at some point, compared with 14.8% on placebo, along with diarrhea (32.0% vs 13.5%) and vomiting (25.3% vs 4.8%). Side effects led 11.2% of people on 12 mg to stop treatment, compared with 4.6% on placebo. For how long they lasted and less common effects, see the retatrutide side effects guide.
Why Results Vary
The averages above hide differences between people. The published data show three that matter:
The first two rows count everyone randomized in TRIUMPH-1; the TRIUMPH-2 figure is Lilly's, for people who stayed on treatment. More on the diabetes trials is in retatrutide for type 2 diabetes. The scale shows total weight, not just fat; what is known about lean mass is covered in does retatrutide cause muscle loss, and the drug itself is explained in what is retatrutide.
Sources
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514–526. DOI: 10.1056/NEJMoa2301972. (Phase 2, including supplementary appendix)
- Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med. Published September 29, 2026. DOI: 10.1056/NEJMoa2604169. (TRIUMPH-1)
- Eli Lilly. Lilly's triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial. December 11, 2025. (TRIUMPH-4)
- Eli Lilly. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. May 21, 2026. (TRIUMPH-1 topline and extension)
- Eli Lilly. Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. September 29, 2026. (TRIUMPH-2)
Medical disclaimer: This article summarizes published clinical trial results for general information only and is not medical advice. Retatrutide is an investigational drug that is not approved for any use. Individual results in the trials varied. Nothing here is a recommendation to use, seek out or avoid any medication.
Frequently asked questions
In the trials, weight loss built steadily over months. People on 12 mg lost an average of 17.5% of their body weight by 24 weeks and 24.2% by 48 weeks in Phase 2, and 28.3% by 80 weeks in TRIUMPH-1, if they stayed on treatment. The trials did not publish exact figures for individual weeks before 24 weeks. Retatrutide is investigational and not approved.
The trials do not report weekly amounts. Dividing the Phase 2 averages for 12 mg by time gives about 0.7% of body weight per week over the first 24 weeks, when people lost 17.5% on average, and about 0.3% per week from week 24 to 48. These are rough calculations, and the pace varied between people and slowed over time.
The trials did not publish exact figures for the first month or three months. The first reported figure is 17.5% at 24 weeks, about six months, for people on 12 mg in the Phase 2 trial, compared with 1.6% on placebo. Numbers for earlier weeks quoted online are estimates.
In TRIUMPH-1, stomach and bowel side effects were mostly temporary and mild or moderate, and occurred most often while the dose was being increased at the start of treatment. Over 80 weeks on 12 mg, 42.4% reported nausea at some point, compared with 14.8% on placebo.
