Is Weight Regained After Stopping Retatrutide? The Short Answer

Retatrutide itself has not been tested yet, but in trials of related drugs a substantial part of the lost weight came back within a year of stopping. In withdrawal trials of two related medicines, people switched to placebo regained weight within a year while those who continued treatment kept it off:

• Tirzepatide (SURMOUNT-4): after losing 20.9%, people switched to placebo saw their weight rise by 14.0% over 52 weeks. Only 16.6% of them kept at least 80% of their earlier weight loss, compared with 89.5% of those who continued.
• Semaglutide (STEP 4): after losing 10.6%, people switched to placebo regained 6.9% over 48 weeks, while those who continued lost a further 7.9%.

Retatrutide's published trials followed participants for four weeks after the last dose but did not report their weight in that period. TRIUMPH-6, a trial that switches some participants to placebo after 80 weeks, is designed to answer the question directly (evidence for retatrutide: none published yet; evidence for the drug class: two large randomized withdrawal trials).

What Retatrutide's Own Trials Show

In the 48-week Phase 2 trial of retatrutide (New England Journal of Medicine, 2023), "participants proceeded to a 4-week safety follow-up period" after treatment ended. TRIUMPH-1, published in the same journal in September 2026, had 80 weeks of treatment followed by 4 weeks of follow-up. Neither paper reports body weight after treatment stopped, so claims that "regain begins within two to three weeks" of stopping retatrutide are not based on published retatrutide data.

What the trials do show is that weight kept falling through the end of treatment. In TRIUMPH-1, about 500 participants (532 with a BMI of 35 or more, according to the company) continued into a 24-week extension at the highest dose they tolerated, 9 mg or 12 mg; those originally assigned to 12 mg had lost 29.9% of their weight at week 104. How the loss built up is covered in the retatrutide weight loss timeline.

TRIUMPH-6: The Trial That Will Test Stopping

The developer's trial listing gives a target of 643 adults with obesity and without diabetes for TRIUMPH-6 and shows enrollment as complete. All participants take retatrutide for an initial 80-week phase. They are then randomly assigned, without knowing which, to continue the same dose, switch to a lower retatrutide dose or switch to placebo for 36 weeks. The placebo group will show what happens to weight after retatrutide is stopped, compared with people who continue. The listing shows the trial running until April 2028.

What Withdrawal Trials of Similar Drugs Show

Two large randomized trials, STEP 4 (semaglutide) and SURMOUNT-4 (tirzepatide), both approved medicines compared in retatrutide vs tirzepatide vs semaglutide, tested what happens when people who have lost weight on a GLP-1-based medicine are switched to placebo.

In STEP 4, published in JAMA in 2021, adults lost 10.6% of their weight during a 20-week run-in on semaglutide 2.4 mg. Over the next 48 weeks, those switched to placebo regained weight (+6.9%), while those who continued lost more (−7.9%).

In SURMOUNT-4, published in JAMA in December 2023, adults lost 20.9% during a 36-week lead-in on tirzepatide. Over the next 52 weeks, those switched to placebo regained 14.0%, while those who continued lost a further 5.5%. At the end, 89.5% of people who continued tirzepatide had kept at least 80% of their earlier weight loss, compared with 16.6% of those switched to placebo. Even so, the placebo group remained 9.9% below their starting weight after 88 weeks, compared with 25.3% for those who continued. The authors concluded that withdrawing tirzepatide "led to substantial regain of lost weight."

Would Retatrutide Be Different?

It might or might not be. Retatrutide acts on the glucagon receptor as well as the GIP and GLP-1 receptors, and it produced larger average weight loss in its trials than semaglutide or tirzepatide did in theirs, although the trials were not head-to-head. Whether those differences change what happens after stopping, for example how fast or how much weight returns, is unknown. Online figures that "project" retatrutide's regain by applying the semaglutide or tirzepatide results are estimates, not data.

Side Effects After Stopping Retatrutide

How long side effects last after the last dose has not been reported. The Phase 2 paper says retatrutide has "a half-life of approximately 6 days," meaning the amount in the body falls by about half every six days, so the drug takes weeks rather than days to clear. Neither the Phase 2 paper nor the TRIUMPH-1 paper describes how side effects such as nausea or dysesthesia changed during the follow-up after treatment ended.

During treatment, gastrointestinal side effects in TRIUMPH-1 were described as mostly temporary and mild or moderate.

What Is Still Unknown

• How much weight people regain after stopping retatrutide, and how quickly.
• Whether a lower dose can maintain weight loss; TRIUMPH-6 includes a switch to a lower dose.
• How long side effects last after stopping.
• Whether improvements in blood pressure, blood sugar and other measures reverse after stopping.
• Whether lean mass changes after stopping; what is known about retatrutide and muscle loss comes from treatment only.

Retatrutide is an investigational medicine and is not approved for any use.

Sources

• Aronne LJ, Sattar N, Horn DB, et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial. JAMA. 2024;331(1):38–48. Published online December 11, 2023.
• Rubino D, Abrahamsson N, Davies M, et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial. JAMA. 2021;325(14):1414–1425.
• 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.
• 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)
• ClinicalTrials.gov. A Study of Retatrutide (LY3437943) in the Maintenance of Weight Reduction in Individuals With Obesity (TRIUMPH-6). NCT06859268.

Medical Disclaimer: This article summarizes published research for general information only and is not medical advice. Retatrutide is investigational and is not approved by the FDA for any use. It is not available by prescription, and products sold online under its name are not sold or supplied by Lilly. Nothing here is a recommendation to start, continue or stop any medication.