Retatrutide vs tirzepatide

Is the triple agonist a real step up from the dual — and can you tell yet?

No head-to-head trial — cross-trial comparison
In one paragraphRetatrutide's phase 3 topline results — about 28% average weight loss at 80 weeks — are higher than tirzepatide's 20–21% in comparable trials, but no study has compared the two directly, and retatrutide's results are not yet peer-reviewed. Retatrutide also reports more discontinuation for side effects and a skin-sensation effect not seen with tirzepatide. Tirzepatide is an approved medicine; retatrutide is not available outside trials.

Side by side

B RetatrutideA Tirzepatide
LYO grade (weight)BA
Best trial weight loss−28.3% at 80 wk (TRIUMPH-1, topline)−20.9% at 72 wk (SURMOUNT-1, published)
Head-to-head trialCross-trial comparison onlyNoneNone
ReceptorsGIP + GLP-1 + glucagonGIP + GLP-1
Peer-reviewed phase 3Not yetYes (multiple)
Stopped for adverse events11–18% vs 4–5% placebo (topline)~4–7% vs ~3% placebo (SURMOUNT-1)
Distinct side effectDysesthesia 9–21% (TRIUMPH-4)Not reported
Regulatory statusInvestigational — trials onlyApproved (EU, US, UK)
Verdict

Probably more weight loss from retatrutide, with more side effects, on numbers that cannot yet be checked. Tirzepatide is the one with published, approved, prescribable evidence. Any product sold today as retatrutide is unlicensed.

Why the comparison is provisional

Both drugs are Lilly's, and the trial programmes were designed with similar populations and endpoints, which makes the cross-trial comparison less unreliable than most. It is still a comparison of two press releases against a set of journal papers. Until TRIUMPH is published, the retatrutide numbers cannot be examined for the things that change conclusions: dropout handling, baseline differences, subgroup effects.

What the third receptor buys — and costs

Adding glucagon-receptor activity is thought to raise energy expenditure and drive liver-fat loss, which plausibly explains the extra weight loss. The same pharmacology raises heart rate and blood glucose in isolation, and the phase 3 programme reports a dysesthesia signal — altered skin sensation in up to a fifth of participants — that is new for the class. Whether it is transient is not yet known.

Questions people actually ask

Is retatrutide stronger than tirzepatide?
The topline weight-loss numbers are higher — roughly 28% versus 21% in comparable trials — but there is no direct comparison and the retatrutide data are unpublished. Higher, probably; by how much, unknown.
When will retatrutide be approved?
Lilly has indicated it will file after the TRIUMPH programme completes. No approval date exists; anything sold as retatrutide today is unlicensed.

References

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