Adverse effect · Retatrutide

How common is GI side effects with Retatrutide?

B
Grade B — probable, not settledPhase 2 + phase 3 topline · effect size: large · adverse
Short answerProbable, not settled. Human data exist (Phase 2 + phase 3 topline) and mostly agree, showing a large effect — but too few, too small, or not yet peer-reviewed for a firm answer. TRIUMPH-4: nausea 38–43% vs 11%, vomiting 20–21% vs 0%; discontinuation for adverse events 12–18% vs 4%. TRIUMPH-1: 11.3% stopped on 12 mg vs 4.9% placebo.

What the studies show

TRIUMPH-4: nausea 38–43% vs 11%, vomiting 20–21% vs 0%; discontinuation for adverse events 12–18% vs 4%. TRIUMPH-1: 11.3% stopped on 12 mg vs 4.9% placebo.

Human trials exist and mostly agree, but there are too few of them, they are too small, or one big one is still reading out. Expect the grade to move.

  1. 1
    Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial.N Engl J Med, 2023;389:514–526338 adults; −24.2% at 48 weeks on 12 mg.
  2. 2
  3. 3
    Eli Lilly. Retatrutide TRIUMPH-1 topline results (NCT05929066).Press release, May 20262,339 adults, 80 weeks plus 104-week extension. Detailed data promised for the ADA Scientific Sessions; not peer-reviewed at time of review.

In context

Retatrutide is an investigational once-weekly peptide that activates three receptors at once: GIP, GLP-1 and glucagon. Phase 3 topline results announced in December 2025 and May 2026 report average weight loss of about 26–29% at 68–80 weeks — the largest yet for a single drug — with high rates of nausea and more people stopping for side effects than on placebo. The full data are not yet peer-reviewed. It is not approved anywhere, and no legitimate supply exists outside clinical trials.

Retatrutide is investigational. Legal status differs by country — see the regulation section or the jurisdiction pages.

Questions

Is Retatrutide proven to cause GI side effects?
Not yet settled. Phase 2 + phase 3 topline — LYO grades it B, meaning probable but liable to change as trials read out.
What studies are behind the grade?
TRIUMPH-4: nausea 38–43% vs 11%, vomiting 20–21% vs 0%; discontinuation for adverse events 12–18% vs 4%. TRIUMPH-1: 11.3% stopped on 12 mg vs 4.9% placebo.
Is Retatrutide approved for this?
No. Retatrutide is investigational; it is not an approved medicine for any indication in the jurisdictions LYO covers.

Other outcomes for Retatrutide

Reviewed 2 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →