Retatrutide Dosage & Dosing Guide
Retatrutide is not FDA approved. This page documents the dosing protocols used in clinical trials. It is not prescribing guidance. All data below comes from published peer-reviewed trials and Eli Lilly press releases. Consult a qualified healthcare provider for any medical decisions.
Retatrutide (LY3437943) is an investigational triple-agonist drug administered as a once-weekly subcutaneous injection. In clinical trials, it has been tested at doses ranging from 1mg to 12mg, with a gradual titration schedule designed to reduce gastrointestinal side effects. This page covers the dosing protocols used in trials, what each dose level achieved, and how the dosing approach compares to existing GLP-1 drugs.
Clinical Trial Dosing Schedule
The dosing protocol used in retatrutide trials follows a stepwise titration — starting at a low dose and increasing every four weeks until the target dose is reached. This is the escalation schedule used in the Phase 2 obesity trial (NEJM 2023, NCT04881760) for participants assigned to the 12mg dose group:
| Week | Dose | Notes |
|---|---|---|
| Weeks 1-4 | 1 mg | Starting dose |
| Weeks 5-8 | 2 mg | First escalation |
| Weeks 9-12 | 4 mg | Second escalation |
| Weeks 13-16 | 8 mg | Third escalation |
| Weeks 17-20 | 12 mg | Fourth escalation — target dose reached |
| Weeks 21-48 | 12 mg | Maintenance at target dose |
Participants assigned to lower target doses followed the same stepwise approach but stopped escalating earlier. For example, those in the 8mg group reached their target at week 13, and those in the 4mg group reached theirs at week 9.
The Phase 2 type 2 diabetes trial (Lancet 2023, NCT04867785) used the same dose escalation protocol across its 36-week study period.
Phase 3 TRIUMPH Titration Schedule
The Phase 3 TRIUMPH program uses a revised titration schedule compared to Phase 2. The most significant change is the addition of a 6 mg intermediate step — Phase 2 jumped directly from 4 mg to 8 mg, while Phase 3 introduces a smoother escalation through 6 mg and 9 mg. For a personalized week-by-week timeline with calendar dates, see the retatrutide dosing calculator.
12 mg target dose (TRIUMPH-1, TRIUMPH-2, TRIUMPH-4)
| Weeks | Dose | Notes |
|---|---|---|
| Weeks 1-4 | 2 mg/week | Starting dose — all participants begin here |
| Weeks 5-8 | 4 mg/week | First escalation |
| Weeks 9-12 | 6 mg/week | New intermediate step (not in Phase 2) |
| Weeks 13-16 | 9 mg/week | Third escalation |
| Weeks 17+ | 12 mg/week | Target maintenance dose reached |
9 mg target dose (TRIUMPH-1, TRIUMPH-2, TRIUMPH-4)
| Weeks | Dose | Notes |
|---|---|---|
| Weeks 1-4 | 2 mg/week | Starting dose |
| Weeks 5-8 | 4 mg/week | First escalation |
| Weeks 9-12 | 6 mg/week | New intermediate step |
| Weeks 13+ | 9 mg/week | Target maintenance dose reached |
4 mg target dose (TRIUMPH-1, TRIUMPH-2 only)
| Weeks | Dose | Notes |
|---|---|---|
| Weeks 1-4 | 2 mg/week | Starting dose |
| Weeks 5+ | 4 mg/week | Target maintenance dose reached |
What changed from Phase 2 to Phase 3
The key differences in the Phase 3 titration schedule:
- 6 mg intermediate step added. Phase 2 jumped from 4 mg directly to 8 mg. Phase 3 adds a 6 mg step, creating a smoother escalation that reduces the size of each dose increase.
- Standardized 2 mg starting dose. Phase 2 tested both 2 mg and 4 mg starting doses. The 4 mg starting dose nearly doubled gastrointestinal side effects compared to 2 mg. Phase 3 exclusively uses the 2 mg start.
- Target doses of 9 mg and 12 mg. Phase 2 tested 1 mg, 4 mg, 8 mg, and 12 mg. Phase 3 focuses on 9 mg and 12 mg as the primary dose arms (with 4 mg included in some trials).
- Longer treatment duration. Phase 2 ran for 48 weeks. TRIUMPH-1, -2, and -3 run for 80 weeks (16 weeks escalation + 64 weeks maintenance). TRIUMPH-4 runs for 68 weeks.
When dose reduction is appropriate
Phase 3 trials include provisions for dose reduction:
- Gastrointestinal adverse events or inadequate oral intake may warrant stepping down to a lower dose level
- BMI reaching 22 kg/m² or below, or perceived excessive weight loss, allows dose reduction
- Treatment is discontinued at BMI 18.5 kg/m² or below
Each four-week dose interval allows roughly one half-life (~6 days) of adjustment time, but does not achieve full steady state — that takes approximately 4-5 half-lives (about 4-5 weeks at a given dose).
How Often and When to Take Retatrutide
Injection frequency
Retatrutide is administered once weekly by subcutaneous injection, on the same day each week. Every clinical trial — Phase 1, Phase 2, and Phase 3 — has used once-weekly dosing exclusively. There is no approved or studied twice-weekly, twice-monthly, or daily dosing regimen.
The once-weekly frequency is possible because of retatrutide's half-life of approximately 6 days. Each injection occurs slightly past one half-life of the previous dose, which maintains consistent therapeutic drug levels.
Best time of day
There is no mandated time of day for retatrutide injection. Clinical trials did not specify morning versus evening dosing. Since retatrutide is a subcutaneous injection (not an oral medication), food timing is irrelevant — it does not need to be taken with or without food.
Some practical considerations:
- Evening injection — some patients prefer injecting in the evening so they can sleep through any initial side effects like nausea
- Consistency matters most — choosing the same day and roughly the same time each week helps maintain stable drug levels
- Injection sites — abdomen, thigh, or upper arm, with rotation between sites to reduce injection-site reactions
What about non-standard intervals (every 5 days)?
Dosing every 5 days instead of every 7 days has not been studied in any retatrutide clinical trial. A 5-day interval would cause faster drug accumulation than what was tested, potentially increasing side effects without proven additional benefit. There is no clinical evidence supporting altered intervals. All dosing data — efficacy and safety — is based on 7-day intervals.
How Long Is a Retatrutide Treatment Course?
Clinical trial treatment durations
| Trial | Treatment Duration | Notes |
|---|---|---|
| Phase 2 (obesity) | 48 weeks | Weight curves were still declining at endpoint |
| Phase 2 (type 2 diabetes) | 36 weeks | Shorter study, same escalation protocol |
| TRIUMPH-1 | 80 weeks | 16 weeks escalation + 64 weeks maintenance |
| TRIUMPH-2 | 80 weeks | 16 weeks escalation + 64 weeks maintenance |
| TRIUMPH-3 | 80 weeks | 16 weeks escalation + 64 weeks maintenance |
| TRIUMPH-4 | 68 weeks | Adults with obesity and knee osteoarthritis |
Is retatrutide a fixed "cycle"?
Retatrutide is not expected to be used as a fixed cycle with a stop date. At 48 weeks in the Phase 2 trial, weight-loss curves were still declining — participants had not reached a plateau. The Phase 3 TRIUMPH trials extend treatment to 68-80 weeks for the same reason: to observe whether and when weight loss stabilizes.
Like other GLP-1 class drugs (semaglutide, tirzepatide), retatrutide is expected to be used as ongoing chronic treatment. Clinical experience with approved drugs in this class shows that weight regain typically occurs after discontinuation, which supports long-term use rather than time-limited cycles.
Dose reduction as weight targets are reached
Phase 3 trial protocols allow dose reduction when a participant's BMI drops to 22 kg/m² or below, or when there is perceived excessive weight loss. This suggests the eventual prescribing approach may involve reaching a target weight and then adjusting the dose downward to maintain it, rather than stopping treatment entirely.
How Dose Titration Works
Why start low
Gradual titration is standard practice across the GLP-1 drug class. The purpose is to give the body time to adapt to the drug's effects — particularly the slowing of gastric emptying — before increasing to a higher dose. Starting at a high dose without titration causes significantly more gastrointestinal side effects.
The Phase 2 trial design tested this directly. Some participants escalated from a 2mg starting dose while others started at 4mg before reaching the same target. The data showed that GI side effects nearly doubled when participants jumped straight to higher doses instead of titrating from the lowest starting dose. This finding reinforced the importance of the gradual approach.
The four-week intervals
Each dose is held for four weeks before the next increase. This interval allows:
- GI side effects (nausea, vomiting, diarrhea) from the current dose level to subside
- The body to adapt to the rate of gastric emptying at that dose
- Clinicians to assess tolerability before increasing further
Time to reach maximum dose
At the four-week escalation schedule used in Phase 2 trials, participants reached the 12mg maximum dose at week 20 (after five four-week steps: 1mg, 2mg, 4mg, 8mg, 12mg). The remaining weeks of each trial were spent at the maintenance dose.
Weight Loss by Dose Level
Retatrutide shows a clear dose-response relationship — higher doses produce greater weight loss. Here is a summary of results across the major trials.
Phase 2 Obesity Trial (48 weeks, 338 participants)
| Dose | Weight Loss at 48 Weeks |
|---|---|
| Placebo | -2.1% |
| 1 mg | -8.7% |
| 4 mg | -17.1% to -17.5% |
| 8 mg | -22.1% to -22.8% |
| 12 mg | -22.8% to -24.2% |
The range at each dose level reflects different starting-dose escalation paths (starting from 2mg vs. 4mg). Participants who titrated from the lowest starting dose (2mg) generally achieved slightly better outcomes at the 12mg target.
Source: Jastreboff et al., NEJM 2023
TRIUMPH-4 Phase 3 (68 weeks, 445 participants)
| Dose | Weight Loss at 68 Weeks | Absolute Weight Loss |
|---|---|---|
| Placebo | -2.1% | — |
| 9 mg | -26.4% | -29.1 kg / -64.2 lbs |
| 12 mg | -28.7% | -32.3 kg / -71.2 lbs |
TRIUMPH-4 tested 9mg and 12mg doses over a longer treatment period. The 28.7% mean weight loss at 12mg is the largest reported in any Phase 3 obesity trial to date.
Source: Eli Lilly press release, December 2025
Phase 2 Type 2 Diabetes Trial (36 weeks, 281 participants)
| Dose | Weight Loss | HbA1c Reduction |
|---|---|---|
| Placebo | — | -0.01% |
| 12 mg | -16.94% | -2.02% |
In the type 2 diabetes population, weight loss was lower than in the obesity trial — which is consistent with the pattern seen across all GLP-1 drugs. Patients with T2D typically lose less weight on anti-obesity medications than those without diabetes. The HbA1c reduction of 2.02 percentage points at 12mg brought 67% of participants to normoglycemic levels (HbA1c below 5.7%).
Source: Rosenstock et al., The Lancet 2023
How Retatrutide Dosing Compares
All three current-generation injectable weight loss drugs use once-weekly dosing with gradual titration, but the specific dose ranges and escalation timelines differ.
| Semaglutide (Ozempic/Wegovy) | Tirzepatide (Mounjaro/Zepbound) | Retatrutide | |
|---|---|---|---|
| Frequency | Once weekly | Once weekly | Once weekly |
| Starting dose | 0.25 mg | 2.5 mg | 1 mg (Phase 2 protocol) |
| Maximum dose | 2.4 mg (Wegovy) | 15 mg | 12 mg |
| Escalation interval | 4 weeks | 4 weeks | 4 weeks |
| Time to max dose | ~16 weeks | ~20 weeks | ~20 weeks |
| Number of dose steps | 5 (0.25, 0.5, 1, 1.7, 2.4 mg) | 5 (2.5, 5, 7.5, 10, 15 mg) | 5 (1, 2, 4, 8, 12 mg) |
| Route | Subcutaneous injection | Subcutaneous injection | Subcutaneous injection |
| FDA status | Approved | Approved | Investigational |
The overall dosing philosophy is the same across all three drugs: start low, escalate in fixed intervals, and maintain at the target dose. The main differences are the absolute dose numbers and the number of intermediate steps. Retatrutide's escalation timeline to reach maximum dose is comparable to tirzepatide's.
One notable difference: semaglutide and tirzepatide have established prescribing information with FDA-approved dose ranges and flexibility for clinicians to hold patients at intermediate doses if tolerability is an issue. Since retatrutide is not yet approved, its dosing protocols reflect what was studied in clinical trials, not formal prescribing guidelines. The final approved dosing regimen may differ from what was used in trials.
Half-Life and Once-Weekly Dosing
Retatrutide is designed for once-weekly administration. Its extended duration of action comes from the same pharmacological strategy used in semaglutide and tirzepatide: a fatty acid chain that binds to albumin in the blood, slowing the drug's clearance from the body.
How it works structurally
Retatrutide is a 39-amino acid peptide linked to a C20 fatty diacid moiety. When injected subcutaneously, the fatty acid chain binds to serum albumin — a protein that circulates in the blood with a long natural half-life. This albumin binding acts as a reservoir, releasing the active peptide slowly over time. The result is a half-life long enough to maintain therapeutic drug levels between weekly injections.
Why this matters for dosing
The extended half-life means:
- Once-weekly injections are sufficient — the drug does not need to be taken daily
- Steady-state levels build up over several weeks — this is another reason why gradual titration works well; the body reaches a stable drug level at each dose before the next increase
- Missing a dose by a day or two is less consequential than it would be with a short-acting drug, though consistent weekly dosing is still recommended for optimal results
This half-life extension approach is well-established in the GLP-1 drug class. Semaglutide uses a C18 fatty diacid, and tirzepatide uses a C20 fatty diacid — structurally similar to retatrutide's approach.
Frequently Asked Questions
What is the recommended dose of retatrutide?
There is no recommended dose because retatrutide is not yet FDA approved. The doses studied in clinical trials range from 1mg to 12mg, with 12mg being the highest dose tested and producing the greatest weight loss (-24.2% at 48 weeks in Phase 2, -28.7% at 68 weeks in Phase 3). The TRIUMPH-4 Phase 3 trial tested 9mg and 12mg as the two active dose arms. The final approved dosing, if and when retatrutide receives FDA approval, will be determined by the regulatory review process and may differ from the trial protocols.
How often is retatrutide injected?
Once weekly, by subcutaneous injection. This is the same frequency as semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound).
Why does the dose start so low?
Starting at a low dose and escalating gradually reduces gastrointestinal side effects. In the Phase 2 trial, participants who skipped lower doses and jumped directly to higher ones experienced nearly double the rate of GI side effects compared to those who followed the full titration schedule. The four-week intervals between dose increases give the body time to adapt.
How long does it take to reach the maximum dose?
In the Phase 2 trial protocol, participants reached the 12mg maximum dose at week 20 after five escalation steps (1mg, 2mg, 4mg, 8mg, 12mg), each held for four weeks.
Is 9mg or 12mg better?
Both doses were tested in the TRIUMPH-4 Phase 3 trial. At 68 weeks, the 12mg dose produced -28.7% weight loss compared to -26.4% at 9mg — a difference of approximately 2.3 percentage points. Whether the additional weight loss at 12mg justifies the higher dose depends on individual tolerability and side effect burden. In TRIUMPH-4, the 12mg group had higher rates of dysesthesia (20.9% vs. 8.8% at 9mg) and slightly higher discontinuation rates due to adverse events (18.2% vs. 12.2%). These trade-offs will likely inform how clinicians and the FDA approach the final approved dose range.
What happens if you miss a dose?
Retatrutide's extended half-life means that missing a single dose by a day or two is unlikely to cause a dramatic loss of drug effect. However, no published clinical trial data specifically addresses the impact of missed doses. For approved drugs in the same class (semaglutide, tirzepatide), the general guidance is to take the missed dose as soon as possible if within a few days, then resume the regular weekly schedule. Similar guidance would likely apply to retatrutide, but this has not been formally established.
Can you stay on a lower dose instead of escalating to 12mg?
In clinical trials, participants were assigned to specific dose groups and followed the titration schedule to their assigned target. The Phase 2 trial did include lower-dose groups (1mg, 4mg, 8mg), all of which showed meaningful weight loss, just less than the 12mg group. Whether an approved version of retatrutide will offer flexibility to maintain at intermediate doses — as semaglutide and tirzepatide do — will depend on the FDA-approved prescribing information.
Why is retatrutide not working for me?
If you are in a clinical trial and not seeing expected results, several factors may explain this. First, you may be receiving placebo — most TRIUMPH trials are placebo-controlled, meaning a portion of participants receive an inactive injection. Second, if you are still in the titration phase (the first 16-20 weeks), your dose may not yet be high enough to produce significant weight loss. In the Phase 2 trial, most of the weight loss occurred after participants reached the 8mg or 12mg target dose. Third, individual responses to GLP-1 class drugs vary — some people are biologically more responsive than others. Finally, lifestyle factors (diet, activity level) influence outcomes alongside the medication. If you have concerns about your response, discuss them with your trial site coordinator or healthcare provider.
What is retatrutide's half-life?
The exact half-life of retatrutide has not been published as a specific number in the major trial publications. What is established is that its pharmacokinetic profile supports once-weekly dosing, achieved through a C20 fatty diacid moiety that binds to serum albumin — the same strategy used by semaglutide and tirzepatide, both of which have half-lives of approximately 5-7 days.
How often do you take retatrutide?
Once weekly, by subcutaneous injection, on the same day each week. All clinical trials — Phase 1, Phase 2, and the Phase 3 TRIUMPH program — used once-weekly dosing exclusively. This is the same frequency as semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound). Retatrutide's half-life of approximately 6 days supports this weekly schedule.
What is the best time of day to take retatrutide?
No specific time of day is required. Clinical trials did not mandate morning or evening dosing. Since retatrutide is a subcutaneous injection (not an oral drug), food timing is irrelevant. Some patients prefer evening injection to sleep through mild initial side effects like nausea. The most important factor is consistency — injecting on the same day and roughly the same time each week.
How long do you stay on retatrutide?
Clinical trials have lasted 48 to 80 weeks, and weight-loss curves were still declining at 48 weeks with no plateau. Like other GLP-1 class drugs, retatrutide is expected to be used as ongoing chronic treatment rather than a fixed-length course. Clinical experience with semaglutide and tirzepatide shows weight typically returns after discontinuation, which supports long-term use. Phase 3 trial protocols allow dose reduction at lower BMI levels rather than stopping treatment.
Can you take retatrutide every 5 days instead of weekly?
A 5-day dosing interval has not been studied in any retatrutide clinical trial. All efficacy and safety data is based on 7-day (once-weekly) intervals. Injecting every 5 days would cause faster drug accumulation than what was tested, potentially increasing side effects without proven benefit. There is no clinical evidence supporting any interval other than once weekly.
What is the starting dose of retatrutide?
The starting dose is 2 mg per week. In the Phase 2 trial, Eli Lilly tested both 2 mg and 4 mg starting doses. The data showed that starting at 4 mg nearly doubled gastrointestinal side effects (nausea, vomiting, diarrhea) compared to starting at 2 mg. Based on this finding, all Phase 3 TRIUMPH trials use 2 mg as the universal starting dose, with the first escalation to 4 mg occurring at week 5.
How do you take retatrutide?
Retatrutide is taken as a once-weekly subcutaneous injection — a small needle injected just under the skin, similar to how insulin is administered. Injection sites include the abdomen, thigh, or upper arm, and you should rotate between sites each week. It does not need to be taken with food, and there is no specific time of day required. The dose starts low (2 mg/week) and increases gradually every 4 weeks up to the target dose of 9 mg or 12 mg. See the titration schedule above for the full escalation protocol.
How does GLP-1 dosing work for weight loss?
All GLP-1 weight loss drugs — semaglutide (Wegovy), tirzepatide (Zepbound), and retatrutide — use the same dosing philosophy: start at a low dose and increase gradually over weeks or months. This titration approach minimizes gastrointestinal side effects (nausea, vomiting, diarrhea) by giving the body time to adapt. Most of the weight loss occurs at the higher maintenance doses, not during the initial titration period. Each drug has different dose ranges and escalation timelines, but all are once-weekly subcutaneous injections. For a comparison, see the dosing comparison table above.
Sources
- Giblin, M.J., et al. (2026). Design of the TRIUMPH Phase 3 Program for Retatrutide. Diabetes, Obesity and Metabolism. DOI: 10.1111/dom.70209
- Jastreboff, A.M., et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. DOI: 10.1056/NEJMoa2301972
- Rosenstock, J., et al. (2023). Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-comparator-controlled, parallel-group, phase 2 trial conducted in the USA. The Lancet. DOI: 10.1016/S0140-6736(23)01053-X
- Eli Lilly and Company. (2025). Lilly's retatrutide achieved significant weight loss and pain relief in adults with obesity and knee osteoarthritis. Press release.
- ClinicalTrials.gov: NCT04881760 (Phase 2, Obesity), NCT04867785 (Phase 2, T2D)
Medical Disclaimer
The content on glp3.wiki is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Retatrutide is an investigational drug that has not been approved by the U.S. Food and Drug Administration (FDA) or any other regulatory agency.
The dosing information on this page reflects protocols used in clinical trials and is not prescribing guidance. If and when retatrutide receives FDA approval, the approved dosing regimen may differ from what was studied in trials.
Do not use this information to make decisions about your health without consulting a qualified healthcare provider. Do not attempt to obtain or self-administer retatrutide outside of an approved clinical trial.
If you are considering weight loss medication, talk to your doctor about currently approved options. For information about enrolling in retatrutide clinical trials, visit ClinicalTrials.gov.
This site is not affiliated with Eli Lilly and Company or any pharmaceutical manufacturer.
Sources
- TRIUMPH trial design paper
Diabetes, Obesity and Metabolism
- Phase 2 trial (NEJM)
New England Journal of Medicine
- Phase 2 T2D trial (Lancet)
The Lancet
- TRIUMPH-4 results
Eli Lilly Investor Relations
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