Why is semaglutide approved but retatrutide is not?

The distinction is timing rather than efficacy. Semaglutide's phase-3 obesity program (STEP-1 and follow-on trials) completed and led to FDA approval as Wegovy in June 2021. Its diabetes program had already led to Ozempic approval in December 2017. Retatrutide's phase-2 obesity data (Jastreboff 2023 NEJM) reported ~24% mean weight loss at 48 weeks, which is larger than semaglutide's phase-3 result, but that is phase 2, not phase 3. The phase-3 obesity program for retatrutide (TRIUMPH) is ongoing.

Investigational status is not a judgment that a compound is inferior or unsafe. It is a statement that the definitive regulatory evidence has not yet been generated. Retatrutide is in the same regulatory position that semaglutide was in during 2019 or 2020 — clearly promising, human-evidence-supported, but not yet at the phase-3-completion endpoint.

When the phase-3 TRIUMPH program completes and results are published, retatrutide will presumably move through the FDA review process on a timeline similar to prior GLP-1 receptor agonist programs. Failure at phase 3 (unexpected adverse event patterns, insufficient effect size at defined endpoints) is always possible but the phase-2 signal is strong enough that most observers expect approval.