How often is retatrutide dosed?

Once-weekly, by subcutaneous injection

In the trials retatrutide was administered once weekly by subcutaneous injection. Its half-life is approximately 6 days, which supports a once-weekly interval, with steady state reached in about 4–5 weeks at each dose level.

The escalation the trials used

Rather than starting at the target dose, the trials raised the dose every 4 weeks. The Phase 3 TRIUMPH protocol stepped it up as follows, all once weekly; the Phase 2 trials tested the 0.5 mg to 12 mg weekly range.

• Weeks 1–4: 2 mg once weekly.
• Weeks 5–8: 4 mg once weekly.
• Weeks 9–12: 6 mg once weekly.
• Weeks 13–16: 9 mg once weekly.
• Weeks 17+: 12 mg once weekly (the maximum dose tested).

Why the trials escalated slowly

The stepwise increase was used to give the body time to adapt and to reduce gastrointestinal side effects. Phase 2 data showed that starting at a higher dose (4 mg) increased side-effect rates without improving outcomes, which is why the trials began low and titrated up.

How long the trials ran

The Phase 2 obesity trial ran 48 weeks in 338 adults, and the companion Phase 2 type 2 diabetes trial ran 36 weeks in 281 adults — both with the once-weekly injection maintained across the study.

What the same trials reported alongside those doses

The dose figures above came out of trials that also reported what those doses did. Gastrointestinal effects dominated and tracked with dose: nausea affected up to 60% of participants at 12 mg in Phase 2, and diarrhea 15–33%. Dysesthesia — altered skin sensation, described as tingling or pins-and-needles — was reported in about 21% at the 12 mg dose in TRIUMPH-4, and is specific to retatrutide rather than shared with semaglutide or tirzepatide. Those rates are why the trials escalated the dose in four-week steps instead of starting high.

The full adverse-event profile from these trials, with rates by dose, is on the compound profile: retatrutide side effects.

• Frequency: once weekly, subcutaneous.
• Titration: dose raised every 4 weeks (TRIUMPH: 2 → 4 → 6 → 9 → 12 mg).
• Phase 2 dose range tested: 0.5–12 mg weekly.
• Half-life ~6 days; steady state in ~4–5 weeks per dose level.