In the Phase 3 TRIUMPH-2 trial, every participant started retatrutide at 2 mg once weekly and stepped up every four weeks. The 4 mg arm went 2 to 4 mg. The 9 mg arm went 2, 4, 6, then 9 mg, reaching target at week 12. The 12 mg arm went 2, 4, 6, 9, then 12 mg, reaching target at week 16 (Lilly, 29 September 2026). The 12 mg arm lost 18.8% of body weight at 80 weeks in The Lancet's primary analysis. Retatrutide is investigational. This is a trial protocol, not a dosing guide.
What is the retatrutide dosing schedule in TRIUMPH?
Every TRIUMPH-2 participant started at 2 mg once weekly by subcutaneous injection and stepped up every four weeks to an assigned target, according to Lilly's 29 September 2026 release. The release states that participants "initiated treatment with 2 mg once weekly and increased the dose in a stepwise approach every four weeks."
| Weeks | 4 mg arm | 9 mg arm | 12 mg arm |
|---|---|---|---|
| 0–3 | 2 mg | 2 mg | 2 mg |
| 4–7 | 4 mg | 4 mg | 4 mg |
| 8–11 | 4 mg | 6 mg | 6 mg |
| 12–15 | 4 mg | 9 mg | 9 mg |
| 16–80 | 4 mg | 9 mg | 12 mg |
Bold marks the week each arm reached its target. Week ranges follow from the four-week interval Lilly describes.
What each arm produced at week 80, from the Lancet paper (29 September 2026), in adults with obesity and type 2 diabetes:
| Arm | Treatment-regimen estimand (Lancet primary) | Efficacy estimand (Lilly headline) | Stopped for side effects or death |
|---|---|---|---|
| 4 mg | −11.9% | −12.7% | 4% |
| 9 mg | −16.8% | −19.1% | 12% |
| 12 mg | −18.8% | −20.8% | 8% |
| Placebo | −5.1% | −4.0% | 5% |
The Lancet paper reports −18.8% on 12 mg at week 80 under the treatment-regimen estimand, which counts every randomised participant whether or not they stayed on the drug. Lilly's headline 20.8% uses the efficacy estimand, which estimates the effect had everyone stayed on treatment. The full readout is in retatrutide Phase 3 results.
What we read
Lilly's TRIUMPH-2 release and the TRIUMPH-2 Lancet abstract (both 29 September 2026); the TRIUMPH-1 abstract in NEJM (29 September 2026), which describes "a fixed dose escalation protocol" without listing steps in the abstract; the Phase 2 obesity trial (Jastreboff et al., NEJM 2023); the Phase 1b study (Urva et al., The Lancet 2022); and the DailyMed entries discussed below. We read the Reddit threads linked here between August and October 2026.
How does the Phase 3 ladder differ from Phase 2?
Two dose sets exist and they get mixed up constantly.
Phase 2 (Jastreboff et al., NEJM 2023) tested 1, 4, 8 and 12 mg weekly over 48 weeks, with some arms starting at 2 mg and others at 4 mg. This is the source of the widely quoted 24.2% at 48 weeks on 12 mg. The 4 mg arm lost roughly 17% and the 8 mg arm roughly 22%.
Phase 3 TRIUMPH used 4, 9 and 12 mg, with a 6 mg step on the way up and no 8 mg dose at all. Trials ran 68 to 80 weeks.
If a chart shows 8 mg, it is quoting Phase 2. If it shows 1 mg as a maintenance dose, it is also quoting Phase 2.
| Compound | Phase 3 starting dose | Phase 3 top dose | Step interval |
|---|---|---|---|
| Semaglutide (Wegovy) | 0.25 mg | 2.4 mg | 4 weeks |
| Tirzepatide (Zepbound) | 2.5 mg | 15 mg | 4 weeks, +2.5 mg |
| Retatrutide (TRIUMPH-2) | 2 mg | 12 mg | 4 weeks |
All three drugs escalate on four-week steps. An earlier version of this page called the retatrutide ladder "slower than typical". It is not: tirzepatide reaches 15 mg at week 20 and retatrutide reaches 12 mg at week 16.
Retatrutide dosage chart in syringe units
Trial doses are in milligrams. The volume that contains a given number of milligrams depends on how much liquid the powder was dissolved in. On a U-100 insulin syringe, 100 units equal 1 mL. The arithmetic below is concentration math for the TRIUMPH dose steps, not an instruction to inject anything.
| Dose (mg) | 10 mg vial + 2 mL (5 mg/mL) | 20 mg vial + 2 mL (10 mg/mL) |
|---|---|---|
| 2 | 0.40 mL · 40 units | 0.20 mL · 20 units |
| 4 | 0.80 mL · 80 units | 0.40 mL · 40 units |
| 6 | 1.20 mL · 120 units | 0.60 mL · 60 units |
| 9 | 1.80 mL · 180 units | 0.90 mL · 90 units |
| 12 | 2.40 mL · 240 units | 1.20 mL · 120 units |
Two things fall out of the table. A 10 mg vial holds less than one 12 mg trial dose. And at 5 mg/mL, every step from 6 mg up exceeds a 1 mL syringe. The units are only as right as the vial's real content, which is the problem the next section covers. Per-vial math for 5, 10 and 20 mg is in our retatrutide reconstitution guide.
Why the label milligram is not a measured milligram
A trial dose of 12 mg is 12 mg because a manufacturer under FDA oversight made it. A research vial labelled 20 mg holds whatever the vendor's supplier put in it. Our mirror of public Janoshik reports (crawled 30 June 2026) holds 60 retatrutide tests that state both a label claim and a measured content. The median vial held 110.4% of its label. The range ran from 87.8% (a 10 mg vial measuring 8.78 mg, report 102150) to 143.5% (a 10 mg vial measuring 14.35 mg, report 91618), and 33 of the 60 held more than 110%. Vendors choose which vials to send for testing, so the real spread is likely wider. A 40% overfill shifts every unit count in the table above by 40%. The Janoshik 7,164-tests purity analysis covers cross-vendor variance. If a vial seems to do nothing at a step where trial participants were already losing weight, our retatrutide not working guide covers how to tell an underfilled or wrong vial from a slow response.
Is splitting the dose twice a week better than once weekly?
No trial has compared them. Every published retatrutide study dosed once a week. The Phase 1b study (Urva et al., The Lancet 2022) measured a half-life of "approximately 6 days" and concluded that it "supports once-weekly dosing."
On Reddit, splitting is common. One r/Peptides thread asks, "Reta Users: Anyone ever split their dose like 1mg Day 1 the. 0.5mg three days later?" (1wnphhg). Another compares "splitting their dosing in half and doing it twice a week vs. taking their full amount once a week" (1we78tn). The reasoning offered is fewer GI symptoms from a lower peak. That is plausible pharmacology and untested for this drug. Nobody has published weight or side-effect data comparing the two schedules.
What happens above 12 mg?
Nobody knows. Phase 2 and Phase 3 both stopped at 12 mg. The Phase 1b study's highest group also topped out at 12 mg.
What the data does show is that side effects climbed with dose up to 12 mg. In TRIUMPH-2, nausea went from 14% on 4 mg to 28% on 12 mg, and hypotension from 1% to 6% (details in retatrutide side effects). Weight loss gained less from each step: 9 mg to 12 mg added 2.0 percentage points on the Lancet's primary estimand.
An r/Retatrutide thread titled "High Dose Discussion" opens, "This post is only for people taking doses of 12mg and up" (1wnqebk), with posters describing 25 to 30 mg. Those doses come from vials of unverified content, so even the posters cannot know what they took.
How do people switch from tirzepatide to retatrutide?
The trials give no switching protocol. TRIUMPH-2 started every arm at 2 mg. An r/Peptides thread, "Switching from tirz to Reta" (1vegnt1), asks whether a person on 5 mg tirzepatide should start reta at 1 mg. The question has no published answer. Our retatrutide vs tirzepatide page covers what the two trial programs show side by side.
What the Phase 3 data does not establish
A step-down maintenance dose. TRIUMPH held each arm at its target to week 80. Whether a lower dose keeps the weight off is untested.
Tapering and stopping. GLP-1-class drugs show weight regain after discontinuation. TRIUMPH-2 had a four-week post-treatment follow-up, which is too short to answer this.
Combinations. No published trial pairs retatrutide with another incretin drug.
Regulatory state, October 2026
Retatrutide is not approved by the FDA, EMA, MHRA or any other regulator. Lilly's 29 September 2026 release restates that it "plans to submit a Biologics License Application (BLA) in Q1 2027." Under standard review, a decision would follow in late 2027 or 2028.
Until then there is no legal prescription channel. Retatrutide is not eligible for 503A compounding, covered in our 503A and PCAC analysis. What a gray-market supply of retatrutide costs at these dose steps is in retatrutide price per month.
Sources
- Eli Lilly, TRIUMPH-2 release, 29 September 2026 - dose ladder, efficacy estimand, BLA timing
- Bellido et al., TRIUMPH-2, The Lancet, 29 September 2026 (doi 10.1016/S0140-6736(26)01861-1) - treatment-regimen estimand, adverse events
- Jastreboff et al., TRIUMPH-1, NEJM, 29 September 2026
- Jastreboff et al., retatrutide Phase 2, NEJM 2023
- Urva et al., retatrutide Phase 1b, The Lancet 2022 - half-life
- DailyMed, RETATRUTIDE LYOPHILIZED POWDER (Guangzhou Yixin Cross-border E-commerce Co., Ltd.)
- SURMOUNT-1, tirzepatide titration comparator
- Reddit: split dosing 1wnphhg, split dosing 1we78tn, high dose 1wnqebk, switching 1vegnt1
- Internal: retatrutide side effects, retatrutide Phase 3 results, retatrutide vs tirzepatide, retatrutide reconstitution, retatrutide price per month, 503A and PCAC
Frequently asked
What is the retatrutide dosing schedule in the Phase 3 trials?
TRIUMPH-2 started everyone at 2 mg once weekly and raised the dose every four weeks: 2 then 4 mg for the 4 mg arm; 2, 4, 6, 9 mg for the 9 mg arm; 2, 4, 6, 9, 12 mg for the 12 mg arm, which hit target at week 16 (Lilly, 29 September 2026).
Can you split a retatrutide dose twice a week?
No trial has tested it. Every published retatrutide trial dosed once weekly, and the Phase 1b study measured a half-life of about six days, which is why weekly dosing was chosen. Reddit threads such as "Anyone ever split their dose" describe twice-weekly splitting, but no data compares it with weekly dosing for weight or side effects.
What dose of retatrutide should you start at if switching from tirzepatide?
No published trial gives a switching protocol. The only starting dose in the Phase 3 record is 2 mg weekly, used for every TRIUMPH-2 arm. Reddit threads such as "Switching from tirz to Reta" ask whether 1 mg is the right start. The trials do not answer that, and we will not guess at a conversion between the two drugs.
What does a retatrutide dosage chart look like in units?
Units depend on concentration. On a U-100 syringe, 100 units is 1 mL. A 20 mg vial in 2 mL is 10 mg per mL, so 2 mg is 0.2 mL or 20 units. A 10 mg vial in 2 mL is 5 mg per mL, so 2 mg is 40 units. The chart shows both.
Has anyone studied retatrutide above 12 mg?
Not in any published trial. Phase 2 and Phase 3 both stopped at 12 mg weekly. In TRIUMPH-2, nausea doubled from 14% on 4 mg to 28% on 12 mg, and nobody knows how that curve behaves above 12 mg. A Reddit high-dose thread describes users at 25 to 30 mg on unverified product.
How long does it take to reach 12 mg of retatrutide?
Sixteen weeks in TRIUMPH-2. Participants spent four weeks each at 2, 4, 6 and 9 mg before reaching 12 mg. The 9 mg arm reached its target after twelve weeks, and the 4 mg arm after four. The trials then held the target dose to week 80.
Is research-grade retatrutide dosed the same as the trial dose?
The milligram numbers describe pharmaceutical-grade retatrutide given under supervision. A research vial may hold more or less than its label, or a different compound. In our mirror of 60 public Janoshik retatrutide tests with a measured content, it ran from 87.8% to 143.5% of the label, with a median of 110.4%. A milligram on a vial label is not a verified milligram.