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 published phase 3 result — 25.0% average weight loss at 80 weeks in TRIUMPH-1 — is higher than tirzepatide's 20.9% at 72 weeks in SURMOUNT-1, but no study has compared the two directly. 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)AA
Best trial weight loss−25.0% at 80 wk (TRIUMPH-1, published)−20.9% at 72 wk (SURMOUNT-1, published)
Head-to-head trialCross-trial comparison onlyNoneNone
ReceptorsGIP + GLP-1 + glucagonGIP + GLP-1
Peer-reviewed phase 3Yes (TRIUMPH-1, TRIUMPH-2, TRANSCEND-T2D-1)Yes (multiple)
Stopped for adverse events4–12% vs 5% placebo (TRIUMPH-2, published); up to 18% in press releases~4–7% vs ~3% placebo (SURMOUNT-1)
Distinct side effectDysesthesia 4–7% (TRIUMPH-2, published); 9–21% (TRIUMPH-4, press release)Not reported
Regulatory statusInvestigational — trials onlyApproved (EU, US, UK)
Verdict

Probably more weight loss from retatrutide, with more side effects, from trials that were not run against each other. Tirzepatide is the one with 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. Since 29 September 2026 it compares journal papers on both sides: TRIUMPH-1 and TRIUMPH-2 are published, and their figures, which count everyone randomised (25.0% and 18.8%), are lower than the press releases had reported. It is still not a head-to-head trial — different participants, an 80-week endpoint against a 72-week one — and two of retatrutide's four obesity trials remain unpublished.

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 published weight-loss numbers are higher — 25.0% at 80 weeks against 20.9% at 72 weeks in each drug's main obesity trial — but there is no direct comparison. 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

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5