01 How it works
Retatrutide hits three hormone receptors at once. The GLP-1 and GIP effects reduce appetite and slow digestion, as with tirzepatide. The added glucagon effect appears to raise energy use and help the liver burn fat — which is thought to explain the bigger results, and the more noticeable side effects.
02 Common uses
03 Run profile
Start at 0.5mg once a week, on the same day each week, and step up in small 0.5mg amounts only if you need to. Stay at least two weeks on each dose, and longer if you have side effects. Step up only if weight loss has slowed to less than about 1–2 lb a week. Once you are losing steadily, stay at that dose: there is no need to keep climbing. The stomach effects tend to be stronger than with tirzepatide, so there is no reason to rush a step.
The profile shows the shape. Ask for the numbers for your vial, your goal and your timeline.
04 Pairs well with
05 What to watch for
The same stomach pattern as tirzepatide but more pronounced, plus some people report an odd tingling or sensitivity of the skin. A slower climb, smaller meals and hydration help. Persistent vomiting, severe abdominal pain or skin symptoms that do not settle need medical attention. Not for anyone with a history of medullary thyroid cancer or MEN2.
06 Evidence & status
InvestigationalIn a 48-week phase 2 trial, the highest dose produced about 24% average weight loss. Larger phase 3 trials are under way.
Investigational — not FDA-approved as of this writing. It is still in late-stage clinical trials.
Sources
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 TrialThe New England Journal of Medicine, 2023 · Clinical trial
- Effects of once-weekly subcutaneous retatrutide on weight and metabolic markers: A systematic review and meta-analysis of randomized controlled trialsMetabolism Open, 2024 · Review
- A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Overweight (TRIUMPH-1)ClinicalTrials.gov, 2023 · Trial registry
- A Study of Retatrutide (LY3437943) in Participants With Type 2 Diabetes Mellitus Who Have Obesity or Overweight (TRIUMPH-2)ClinicalTrials.gov, 2023 · Trial registry
- What to know about retatrutideEli Lilly and Company (newsroom), 2026 · Reference
- Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1)Eli Lilly and Company (investor news release), 2026 · Clinical trial
- What pharmacists need to know about retatrutide’s TRIUMPH-1 phase 3 resultsPharmacy Times, 2026 · Reference
- The Prohibited ListWorld Anti-Doping Agency, 2026 · Regulator document
Status and sources last checked November 3, 2026. Something out of date? Tell us.
07 How long until it works
Retatrutide is the fastest-acting of the three weight-loss peptides on this site, and the trial numbers are the reason people ask about it. In the 48-week phase 2 trial, the 12mg dose produced about 24% average weight loss, against about 2% on placebo. In TRIUMPH-1, the first phase 3 trial to report (May 2026), people who stayed on 12mg for 80 weeks lost about 28% on average; counting everyone who started, the figure was about 25%.
As with tirzepatide, the loss comes after the dose has been built up, and the climb is slower here because the stomach effects are stronger. The run profile above starts at 0.5mg and steps up only when loss has slowed; on that approach the first months are about tolerance, and the pace people read about in trial headlines belongs to the higher doses.
08 Retatrutide vs tirzepatide
Tirzepatide acts on GLP-1 and GIP; retatrutide adds glucagon, which appears to raise energy use and liver fat burning. In trials that is roughly the difference between about 21% average weight loss (tirzepatide, SURMOUNT-1, 72 weeks) and about 25–28% (retatrutide, TRIUMPH-1, 80 weeks). Different trials, different people, but the direction is consistent.
The price is tolerability. Stomach effects are more pronounced, and retatrutide has a side effect tirzepatide does not: dysesthesia, an odd skin tingling or sensitivity, reported by about 5% of people on 4mg and about 12% on 9mg and 12mg in TRIUMPH-1, against about 1% on placebo. And tirzepatide is an approved medicine with a label; retatrutide is still investigational.
Sema, Tirz or Reta, side by side →09 Stacking
Retatrutide is run on its own. Nothing has been tested alongside it, and because it is still in trials there is no label to say what it should not be combined with. The reasoning that applies to tirzepatide applies here too: anything that lowers blood sugar needs a doctor’s input, and a recovery peptide during a training block adds its own evidence, not retatrutide’s.
10 Where it stands legally
Retatrutide is not approved anywhere. All four TRIUMPH phase 3 trials have reported, and Lilly has said it plans to file for approval in the first quarter of 2027; a decision would follow months after that. Until then there is no approved product, and because it is neither an approved drug nor on any compounding list, there is no legal route to a compounded version either. It is not among the six peptides in the October 2026 HHS enforcement-discretion policy.
In sport, an unapproved substance falls under S0 of WADA’s Prohibited List, so it is banned at all times for tested athletes; the approved GLP-1 medicines, by contrast, are monitored but not banned.
11 FAQ
Why is it called a triple agonist?
It acts on three receptors — GLP-1, GIP and glucagon — where tirzepatide acts on two and semaglutide on one.
Is the tingling normal?
It has been reported specifically with retatrutide. If it is strong or does not settle, get it checked.
Is it approved anywhere?
Not yet. It is still being studied in clinical trials.
When should I step up?
Only if weight loss has slowed to less than about 1–2 lb a week after at least two weeks on your current dose, and side effects are mild. If you are losing steadily, stay where you are. Step up 0.5mg at a time, never more.
How much weight do people lose on retatrutide?
About 24% on average at 48 weeks on the top phase 2 dose, and about 25–28% at 80 weeks on 12mg in the first phase 3 trial, depending on whether you count everyone who started or only those who stayed on treatment. Averages hide a wide spread.
Why is the climb slower than with tirzepatide?
Because the stomach effects are stronger and there is a second side effect, skin tingling, that rises with the dose. Staying longer on each step is how people keep both manageable.
When will retatrutide be approved?
Lilly has said it plans to submit for approval in early 2027. Approval, if it comes, would be later that year at the earliest. Nothing on this page should be read as a sign it will be approved.
Is retatrutide banned in sport?
Yes, as a non-approved substance under WADA’s S0 category. That changes only if it is approved as a medicine, and even then WADA would decide separately.
Educational information only — not medical advice. The Daily Stack does not sell or supply any products. Talk to a licensed healthcare professional about your own health decisions.