Retatrutide
Triple agonist (GLP-1 + GIP + glucagon) from Eli Lilly. In trials it outperforms Tirzepatide for weight loss.
Retatrutide: Triple agonist (GLP-1 + GIP + glucagon) from Eli Lilly. In trials it outperforms Tirzepatide for weight loss. Retatrutide is the newest weight-loss compound in development at Eli Lilly.
Retatrutide is the newest weight-loss compound in development at Eli Lilly. It's a stronger cousin of Tirzepatide (Mounjaro / Zepbound) and pulls bigger weight loss in trials, often 20%+ of body weight. One injection per week. Side effects are real, especially in the first few weeks.
GLP-1/GIP/glucagon agonists are not on the WADA Prohibited List (semaglutide and tirzepatide sit on the 2026 Monitoring Program only). As an unapproved investigational substance, retatrutide could still be argued under S0 (non-approved substances) for tested athletes, so treat it as risky if you compete.
Not yet available by prescription. Trial-only access through Lilly's clinical program.
Wear a CGM the first 14 days.
Triple-agonist response varies, measure to know. A two-week sensor (~$80, OTC, no prescription) tells you more about how YOUR body is responding to Retatrutide than any protocol guide can. Most users wear one and don't again. The first cycle is the one that matters.
Who it's for
- βPeople plateaued on Tirzepatide
- βUsers targeting >15% body weight loss
- βMetabolic-syndrome adults under provider guidance
What to expect
- Week 1
Appetite drops sharply. Nausea common days 2-4.
- Week 4
First titration step. ~3-6lb down for most users.
- Week 8
Steady-state approaching. Cumulative loss 6-12lb depending on dose.
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How it works (mechanism)
Triple agonist, GLP-1, GIP, and glucagon receptors all activated by one molecule. The glucagon arm adds metabolic-rate elevation (mild thermogenesis) on top of the appetite suppression, driving the largest trial weight-loss effect to date.
Dosing protocol
Stacks well with
Stack essentials
Side effects
When NOT to use
- β History of medullary thyroid carcinoma or MEN-2
- β Pancreatitis history
- β Pregnancy / nursing
Bloodwork to monitor
- β’ Lipid panel
- β’ Liver enzymes (ALT/AST baseline + every 3 mo)
- β’ A1C if metabolic context
Common mistakes
- β’ Titrating too fast, stick to 4-week steps
- β’ Not eating enough protein during the cut (lean mass loss)
- β’ Stopping abruptly with no maintenance plan (rebound common)
What it actually is
Retatrutide is an investigational weekly injection that activates three receptors at once: GLP-1, GIP and glucagon. It is an Eli Lilly compound still in clinical development. It is not approved anywhere, it may not lawfully be used in compounding in the US, and FDA treats consumer sales of it as marketing of an unapproved drug β so a product sold to the public is more accurately described as claiming to contain retatrutide, since nothing about its identity can be verified. Phase 3 trials have now completed and reported, and approval has not followed yet.
Two of retatrutide's three targets are the same appetite and insulin signals tirzepatide uses. The third, glucagon, is the interesting addition. Glucagon is proposed to raise energy expenditure and shift liver fat handling, which is the opposite of what you would want in isolation for blood sugar, but combined with two incretin signals the net result in trials was more weight lost. That energy-expenditure contribution is a working hypothesis built largely on preclinical work rather than a demonstrated human effect, and liver fat reduction on the drug does not by itself prove the glucagon arm caused it.
Forms, and which is which
There is no approved product to compare against, so identity, dose accuracy and sterility rest entirely on the seller and cannot be checked by the buyer. FDA treats consumer sale of these as marketing an unapproved drug.
Verdict: Unverifiable contents, outside any lawful supply route.
The only route where the molecule, dose and sterility are known, with monitoring attached.
Verdict: The only defensible source, and it requires enrolling.
Peptides are less stable in solution than as a dried powder. Worth saying plainly: looking at either one tells you nothing about identity, potency, purity or sterility, so no format here amounts to a quality check.
Verdict: No format of an unverified product is the safer format.
Combines an unapproved compound with another and makes any effect or side effect unattributable.
Verdict: Two unknowns in one syringe.
What it is claimed to do, graded
The phase 2 NEJM trial is randomised, placebo-controlled and reported around 24% mean body weight reduction at 48 weeks at the highest dose. That is real evidence. It is also phase 2, not phase 3, so the long-term safety picture is not complete.
TRANSCEND-T2D-1, a completed 40-week phase 3 randomised double-blind placebo-controlled trial in 537 people, was published in the Lancet in 2026. That is phase 3 evidence, even though the drug is not approved.
A randomised Nature Medicine trial in MASLD showed substantial liver fat reduction. Promising and early.
No head-to-head trial supports this. Gastrointestinal side effects in the phase 2 data were dose-dependent and common.
Completed trials now provide safety observations out to roughly 40 to 48 weeks, so this is no longer a blank. What that cannot establish is rare, long-latency or cardiovascular safety, and the dose-dependent heart rate increase seen in trials remains an open question.
Grades describe how much human evidence exists for that specific claim, not whether it will work for you or whether it is safe.
Pros and cons
- β’ The largest phase 2 weight reduction reported for any obesity drug to date
- β’ Randomised human evidence exists, which separates it from most research peptides
- β’ Weekly dosing
- β’ Liver fat data is genuinely encouraging
- β’ Not approved anywhere, so all non-trial supply is unverified grey market
- β’ Not approved, so the full regulatory safety review has not happened; long-term and rare risks remain open questions
- β’ Dose-dependent heart rate increase was seen in trials
- β’ Gastrointestinal side effects are common and titration steps are where they bite
- β’ Nothing sold has assured identity or sterility
When to stop
- β’ Resting heart rate climbing and staying up
- β’ Severe persistent abdominal pain radiating to the back
- β’ Vomiting that prevents keeping fluids down
- β’ A new neck lump, hoarseness or difficulty swallowing
- β’ Pregnancy, or planning one
Interactions
Additive glucose lowering is expected from the mechanism. Retatrutide has no approved interaction labelling, so no list for it can be treated as complete.
Stacking incretin agonists multiplies gastrointestinal effects and glucose lowering with no evidence of added benefit.
Delayed gastric emptying alters absorption rate.
Retatrutide raised heart rate in trials. Compounding that with stimulants is a theoretical concern rather than a characterised interaction.
General weight-loss guidance extrapolated here, not a retatrutide trial finding β no trial cited on this page randomised people to protein or resistance training.
Is this for you?
- β’ Participation in an authorised clinical trial is the only context in which this compound is lawfully available
- β’ Anyone comparing it against the approved GLP-class options with a clinician, on the published trial data
- β’ You want an approved medicine with a known long-term safety profile β this is not that yet
- β’ Personal or family history of medullary thyroid carcinoma or MEN-2
- β’ Prior pancreatitis
- β’ You have a cardiac arrhythmia or uncontrolled hypertension
- β’ Pregnant, nursing or trying to conceive
The one number
Sources for the claims above
- Phase 2 weight reduction at 48 weeks
- Phase 3 randomised double-blind trial in type 2 diabetes (TRANSCEND-T2D-1)
- Phase 2 randomised trial in type 2 diabetes
- Randomised trial in metabolic dysfunction-associated steatotic liver disease
Drug & supplement interactions
- β Same class warnings as Tirzepatide: insulin dose reduction, gastric-emptying delays, contraceptive absorption
- β Glucagon arm may slightly elevate heart rate, caution with stimulants
The Pepdex take
Pepdex take: 4mg weekly is the typical maintenance dose. Nausea profile is rougher than Tirzepatide for the first 2-3 weeks, eases by week 3 in most users. Splitting the weekly dose into two half-doses doesn't help, it just spikes side effects on each split, no smoother on either. The trial data on Reta is the strongest in the GLP class. Pre-FDA, so source quality matters more here than with approved alternatives.
Community patterns
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Common questions about Retatrutide
Tracked alongside Retatrutide
Same goal, different aisle β each graded on its own evidence in the Pepdex catalog.
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