Retatrutide Dosing Schedule: What the Trials Did, Week by Week

Why does retatrutide need a dosing schedule?

A dosing schedule is the sequence of doses a participant receives over time, week by week. Retatrutide needs one for the same reason every GLP-1 receptor agonist does: the gastrointestinal side effects (nausea, vomiting, diarrhoea, constipation) are dose-related and worst in the first weeks at any new dose.

The NEJM phase 2 paper states this directly: adverse events were dose-related, mostly mild to moderate, and partially mitigated by a lower starting dose. So every trial arm above 1 mg climbed to its maintenance dose in steps.

There is a second reason that is easy to miss. Retatrutide has a half-life of approximately 6 days, so each weekly dose stacks on what is left of the previous ones. Blood levels keep rising for about a month after any dose change. A step every 4 weeks lets each level settle before the next increase, which is why the phase 2 escalation windows are multiples of four weeks. The pharmacokinetics are laid out in the half-life guide.

What was the phase 2 obesity dosing schedule?

The NEJM trial (338 adults, 48 weeks) randomised participants in a 2:1:1:1:1:2:2 ratio to placebo or to six retatrutide arms: 1 mg, 4 mg with a 2 mg start, 4 mg with a 4 mg start, 8 mg with a 2 mg start, 8 mg with a 4 mg start, and 12 mg with a 2 mg start.

The ClinicalTrials.gov entry describes the 12 mg arm as "2 mg starting dose followed by 4 mg, 8 mg and then 12 mg" and states that escalation "occurred in certain treatment groups up to Week 12". Three steps within twelve weeks is a 4-week cadence, and that is what the timeline below shows for the top arm.

The 8 mg arms tell the titration story. The slow arm went 2 mg, 4 mg, 8 mg; the fast arm went 4 mg, 8 mg. Both reached the same maintenance dose and, pooled, the same 48-week result of -22.8%. The difference showed up in tolerability, not efficacy, and that comparison is the subject of the titration guide. The 1 mg arm had no escalation at all: it started and stayed at 1 mg, and finished at -8.7%.

What was the phase 2 type 2 diabetes schedule?

The Lancet 2023 trial (281 adults with type 2 diabetes, 36 weeks) used the same ladder shifted down one rung: 0.5 mg fixed, 4 mg with a 2 mg start, 4 mg without escalation, 8 mg with a 2 mg start (slow), 8 mg with a 4 mg start (fast), and 12 mg with a 2 mg start.

The registry describes the 12 mg arm as "2 mg starting dose followed by 4 mg, then 8 mg, then 12 mg". The primary endpoint was HbA1c at 24 weeks; weight and HbA1c were measured again at 36 weeks. An active comparator, dulaglutide 1.5 mg weekly, ran alongside.

What is the phase 3 TRIUMPH dosing schedule?

The TRIUMPH design paper (Diabetes, Obesity and Metabolism, 2025) describes four phase 3 trials in more than 5,800 participants. TRIUMPH-1 and TRIUMPH-2 test 4, 9 and 12 mg once weekly against placebo; TRIUMPH-3 (cardiovascular disease) and TRIUMPH-4 (knee osteoarthritis) test 9 and 12 mg.

Every arm follows a "fixed dose escalation regimen" lasting 16 weeks, then 64 weeks of maintenance, for 80 weeks of treatment; TRIUMPH-4 stops at 68 weeks. The paper says doses and escalation were selected from the phase 1 and 2 safety, efficacy and exposure-response data. It does not print the intermediate steps, so neither does this page.

Two details from the registry entries matter for anyone reading the schedule. TRIUMPH-1 includes an extension subset that continues retatrutide for a further 24 weeks after the placebo-controlled period, with weight measured at week 104. And all four trials add a 4-week safety follow-up after the last dose, which is roughly five half-lives.

The phase 1b and TRANSCEND schedules

The earliest human schedule is in the 2022 Lancet phase 1b paper: 72 adults with type 2 diabetes received weekly doses for 12 weeks in groups of 0.5 mg, 1.5 mg, 3 mg, 3 then 6 mg, and 3 then 6 then 9 then 12 mg. The top group therefore reached 12 mg inside 12 weeks, an escalation faster than anything used later. The paper reported dose-proportional pharmacokinetics and a half-life of approximately 6 days.

The first phase 3 publication, TRANSCEND-T2D-1 in the Lancet (June 2026), randomised 537 adults with type 2 diabetes to 4, 9 or 12 mg once weekly or placebo for 40 weeks. Mean weight change was -11.5%, -13.9% and -15.3% and HbA1c fell 1.69, 1.86 and 1.94 percentage points. Discontinuation of the study drug for adverse events was 2 to 5% with retatrutide and 0% with placebo, and the gastrointestinal events were described as mild to moderate and subsiding over time.

Were dose reductions allowed?

Yes, in phase 3. The TRIUMPH design paper permits a permanent dose reduction for gastrointestinal adverse events or inadequate oral intake that have not improved with other measures, including a prior de-escalation and re-escalation attempt. A reduction is also allowed for participants who reach a BMI of 22 kg/m2 or lower, or who feel they have lost too much weight. That last clause is unusual in an obesity trial and reflects the size of the effect at 12 mg.

All retatrutide dosing schedules in one table

The pattern across five years of trial protocols is consistent: one injection a week, a low first dose, steps of roughly a doubling, and a long flat maintenance phase. What changed between phase 2 and phase 3 is the length of the climb (12 to 16 weeks) and the rungs (8 mg replaced by 9 mg). The results each schedule produced are collected in the results page, and the overall dose picture in the retatrutide dosage guide.

Back to the retatrutide dosage guide