The short version
- No published retatrutide trial used cycles: dosing was continuous and weekly for 12 weeks (phase 1b), 36 to 48 weeks (phase 2) and 40 to 104 weeks (phase 3).
- Weight was still falling at week 48 in the 8 mg and 12 mg phase 2 arms (-22.8% and -24.2%), which is why the phase 3 trials set their primary endpoint at week 80.
- A single dose reduced body weight for up to 43 days in the phase 1 study, consistent with the approximately 6-day half-life; the compound is essentially cleared about six weeks after the last dose.
- No off-treatment follow-up data for retatrutide has been published; the nearest evidence on stopping is the tirzepatide withdrawal trial SURMOUNT-4.
Why there is no retatrutide cycle in the literature
The word "cycle" describes compounds taken for a fixed number of weeks and then stopped for a fixed number of weeks. Retatrutide was never studied that way. It is an incretin-class peptide developed for chronic weight and glucose management, and every trial in the published record dosed it continuously: one subcutaneous injection a week, for as long as the trial lasted.
Searches for a retatrutide cycle length are therefore asking a question the data cannot answer; the question the data does answer is how long the trials dosed it, and what they observed over that time.
No trial ever stopped and restarted the drug. People took it every week for the whole study.
How long did the trials dose retatrutide?
Laid end to end, the durations show the program lengthening as the evidence accumulated. The phase 1b multiple-ascending-dose study (Lancet 2022) ran 12 weeks. The phase 2 diabetes trial (Lancet 2023) ran 36 weeks and the phase 2 obesity trial (NEJM 2023) ran 48 weeks. The phase 3 TRANSCEND-T2D-1 trial ran 40 weeks, and the four TRIUMPH obesity trials run 68 to 80 weeks of treatment, with a subset of TRIUMPH-1 continuing to week 104.
In none of these was there a planned break. The TRIUMPH design paper describes a 4-week safety follow-up after the last dose, which is the only off-drug period in the program, and it exists to record late adverse events, not to measure regain. The week-by-week dose ladders inside those durations are in the dosing schedule guide.
Weight was still falling at week 48
The phase 2 curve itself explains why the trials kept getting longer. At 24 weeks the 8 mg and 12 mg groups were at -17.3% and -17.5%; at 48 weeks they were at -22.8% and -24.2%. That is another 5 to 7 points in the second half of the trial, with no plateau described in the abstract.
The 4 mg group moved from -12.9% to -17.1% over the same period. A trial that had stopped at week 12 or 16, when escalation ends, would have recorded less than half of the effect the 48-week trial eventually measured.
The phase 3 designers drew the conclusion and set the primary endpoint at week 80. Until those trials publish, the 48-week NEJM data is the longest continuous exposure with peer-reviewed results, collected dose by dose in the results page.
What is known about stopping
For retatrutide specifically, nothing has been published. No trial has reported weight after withdrawal of the drug. The nearest evidence is from tirzepatide, the dual GIP and GLP-1 agonist from the same manufacturer.
In the SURMOUNT-4 withdrawal trial (JAMA 2024), 670 adults who had lost a mean 20.9% over 36 weeks on tirzepatide were randomised to continue or switch to placebo: over the next 52 weeks the placebo group regained 14.0% while the continuing group lost a further 5.5%. The direction is likely to be similar for retatrutide; the magnitude is unknown, since retatrutide adds glucagon receptor activity and produced larger losses.
What the pharmacology does establish is how fast the drug itself leaves. With a half-life of approximately 6 days, 50% of the last dose is gone in 6 days, 75% in 12, about 97% in 30 and more than 99% in 42. The compound is effectively cleared within six weeks; whatever happens to appetite and weight after that is biology, not residual drug. The decay curve is drawn in the half-life guide.
The drug itself is gone about six weeks after the last dose. What weight does after that has not been measured for retatrutide.
One dose, 43 days of effect
There is one striking data point about duration in the earliest paper. In the phase 1 single-ascending-dose study reported in Cell Metabolism (2022), "a reduction in body weight persisted up to day 43 after a single dose". One injection, six weeks of measurable effect.
That is what a 6-day half-life looks like in a drug with a large effect size: the exposure fades over a month, and the weight response lags behind it. It is also why the trials could escalate in 4-week steps and still see each level settle before the next.
Duration, for the record
For a study that references the clinical program, the durations to carry over are: weekly exposure, a 12 to 16 week escalation, a maintenance phase of at least 36 weeks in every trial with results, and 80 weeks as the phase 3 standard.
The concept of a cycle has no source in this literature, and a design that borrows it is not modelling the human data. The dose levels themselves are on the retatrutide dosage guide, and the phase 3 program in detail in the TRIUMPH and TRANSCEND guide.
Questions readers ask
Did any retatrutide trial use cycles?
No. Every trial dosed continuously once a week: 12 weeks in phase 1b, 36 and 48 weeks in phase 2, and 40 to 80 weeks (104 with the extension) in phase 3. The word cycle does not appear in the protocols.
Did any trial stop and restart retatrutide?
No. The only planned changes are dose reductions for tolerability. TRIUMPH trials include a 4-week safety follow-up after the last dose, and TRIUMPH-1 has a 24-week extension where a subset continues on drug, not off it.
How long does retatrutide remain in the body after the last dose?
With a half-life of approximately 6 days, about 3% of the last dose remains after 30 days and under 1% after 42 days. The phase 1 single-dose study saw the weight effect persist to day 43.
What happened to weight after participants stopped?
No retatrutide-specific data has been published. For the related dual agonist tirzepatide, the SURMOUNT-4 withdrawal trial reported a 14.0% regain over 52 weeks after switching to placebo, which is the closest published evidence.
Sources
Reviewed against the primary sources on 21 Sep 2026. Every DOI resolves on CrossRef and every NCT number on ClinicalTrials.gov.
- Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine. 2023;389(6):514-526. doi.org/10.1056/NEJMoa2301972
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism. 2022;34(9):1234-1247. doi.org/10.1016/j.cmet.2022.07.013
- Urva S, Coskun T, Loh MT, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. The Lancet. 2022;400(10366):1869-1881. doi.org/10.1016/S0140-6736(22)02033-5
- Giblin A, et al. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism. 2025;28:83-93. doi.org/10.1111/dom.70209
- ClinicalTrials.gov. TRIUMPH-1: retatrutide once weekly in participants without type 2 diabetes who have obesity or overweight. Phase 3; 2,335 participants; primary endpoint at week 80. clinicaltrials.gov/study/NCT05929066
- 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. doi.org/10.1001/jama.2023.24945