Retatrutide: Phase 3 Results, Dosing and Bloods

Educational content only. Not medical advice. Off-label use carries risk.

Why retatrutide is getting attention

Retatrutide is being discussed in bodybuilding circles for cutting phases where athletes want to drop fat while protecting lean tissue. Unlike older incretin drugs such as semaglutide (Ozempic) and the newer tirzepatide (Mounjaro), retatrutide targets three pathways at once: GLP-1, GIP, and glucagon receptors. It is still in clinical trials, yet early data suggest a stronger effect on body composition than previous options.

How it works

GLP-1 reduces hunger and slows gastric emptying. GIP supports insulin action and nutrient handling. Glucagon receptor activation increases baseline energy expenditure and fat oxidation. Together this gives robust appetite control and a modest rise in energy use at rest. In practice that can make a calorie deficit easier to maintain and can smooth out recomposition periods when combined with resistance training and adequate protein.

What the trials actually measured

The reputation comes from a phase 2 trial published in the New England Journal of Medicine in 2023: 338 adults, once-weekly dosing, and a mean weight reduction at 48 weeks of 24.2% on 12 mg and 22.8% on 8 mg. Gastrointestinal effects were the most common adverse events, were dose-related, and were reduced by starting at 2 mg rather than 4 mg. Heart rate rose in a dose-dependent way, peaking at 24 weeks before declining.

A separate phase 2a trial published in Nature Medicine in 2024 examined liver fat in metabolic dysfunction-associated steatotic liver disease. It reported relative reductions in liver fat of up to 86% at 48 weeks, with more than 85% of participants on higher doses reaching a normal liver fat level, alongside improved insulin sensitivity and fasting triglycerides down by more than 40%. Liver enzymes did not change significantly at therapeutic doses.

The phase 3 programme, TRIUMPH, is much larger and reported from late 2025 onwards. TRIUMPH-1 randomised 2,339 adults with obesity or overweight and at least one weight-related condition, without diabetes, over 80 weeks. The manufacturer reported an average weight reduction of 28.3% on 12 mg, with 45.3% of participants losing at least 30% of body weight, and a subgroup starting at a BMI of 35 or above reaching 30.3% at 104 weeks in an extension. On the more conservative treatment-regimen analysis, which counts everyone randomised whether or not they stayed on the drug, the figures were 25.0% on 12 mg against 3.9% on placebo.

Three further trials reported alongside it. TRIUMPH-2, in 1,152 adults, reported 20.8% on 12 mg against 4.0% on placebo. TRIUMPH-3, in 1,949 adults, reported 21.6% to 22.6% on the two higher doses with improvements in lipids, blood pressure, hsCRP and waist circumference; its cardiovascular endpoint returned a hazard ratio of 0.82 with a confidence interval from 0.55 to 1.22, which is too wide to conclude anything in either direction. TRIUMPH-4, in 445 adults with knee osteoarthritis, reported 28.7% at 68 weeks alongside reduced pain and improved physical function.

Read those numbers with one qualification firmly attached. The phase 2 results above are peer-reviewed papers you can read in full. The phase 3 results are company topline announcements: the detailed data are still being presented at medical meetings and submitted to journals, so figures may be refined and the complete safety and subgroup picture is not yet public. They are the best evidence available on retatrutide at scale, and they are not yet the same kind of evidence as the two trials above.

Two things follow. The measurable effects are metabolic, which means glucose handling, insulin sensitivity, triglycerides and liver fat are where the change shows up first, and all of them are visible in blood work. And the doses in those trials are the doses in the protocol below, which is worth remembering before treating 12 mg as a casual number.

Sources: Jastreboff AM et al., Triple–Hormone-Receptor Agonist Retatrutide for Obesity, A Phase 2 Trial, New England Journal of Medicine, 2023; Sanyal AJ et al., Retatrutide for metabolic dysfunction-associated steatotic liver disease, a randomized phase 2a trial, Nature Medicine, 2024; Eli Lilly, TRIUMPH-1 topline results, May 2026 (company announcement, not peer reviewed); Eli Lilly, TRIUMPH-4 topline results, December 2025 (company announcement, not peer reviewed).

Who might consider it

Competitive athletes and enhanced users often look at incretin drugs during a cut to manage appetite and blood glucose while keeping training quality high. The same logic that drew people to Ozempic and Mounjaro applies here. Retatrutide may be more potent, so planning and monitoring matter even more.

Key risks and what to watch

• Gastrointestinal effects: nausea, bloating, constipation. Usually dose related.
• Lean mass loss: more likely with fast weight loss and low protein. Mitigate with strength work and adequate calories from protein.
• Gallbladder issues: risk increases with rapid fat loss.
• Pancreatitis: rare but serious. Any severe abdominal pain needs urgent assessment.
• Heart rate: small increases are reported with incretin therapies.
• Unknowns in lean athletes: long-term data in this group are limited.
• Altered skin sensation: dysesthesia was reported in roughly one in ten participants on the highest doses in TRIUMPH-1, generally mild to moderate, and mostly resolving during treatment.
• Urinary tract infections: also reported in roughly one in ten on the highest doses in the same trial.
• Not tolerating the dose: in TRIUMPH-1, 4.1% stopped because of side effects on 4 mg, 6.9% on 9 mg and 11.3% on 12 mg, against 4.9% on placebo. The chance of having to come off rises with the dose.

Blood tests before, during and after

The markers worth tracking are the ones the trials moved: fasting glucose, HbA1c, fasting insulin, a full lipid profile, ALT, AST, GGT, creatinine, eGFR, electrolytes, TSH and FT4, and a full blood count. Add CRP if inflammation is a concern. Monitor resting heart rate and blood pressure at home each week, and take hydration and electrolytes seriously during aggressive fat loss.

Before you start

Take a baseline one to two weeks before the first dose, while nothing has changed. The Sports Performance Blood Test covers most of it in a single venous draw: HbA1c, a complete cholesterol profile, liver and kidney function, a full blood count, thyroid, hormones and CRP. Add the HbA1c and Fasting Glucose Blood Test and the Fasting Insulin Blood Test for the fasting pair, since insulin sensitivity is the marker most likely to move first. For a fuller cardiovascular baseline, the Longevity Blood Test extends the same list to 70 markers with apolipoprotein B, lipoprotein(a), homocysteine and vitamin D.

During the cycle

Every four to six weeks, and sooner if symptoms change. Rotating focused panels is cheaper than repeating everything: HbA1c and fasting glucose, fasting insulin, the Cholesterol Profile, the Advanced Liver Function panel, which carries AST alongside ALT, GGT and ALP, and kidney function with urea and electrolytes, which matters most during aggressive fat loss when hydration and sodium are under strain.

After you finish

Repeat the baseline panel four to eight weeks after the taper ends. That comparison is what tells you what the cycle actually did: which markers improved and held, which drifted back, and whether the fat loss cost you anything measurable. Console charts every marker across all three stages, so before, during and after read as one line rather than three unrelated result sheets. Compare panels in blood sugar and metabolic tests or across the full range of blood tests.

How it compares to semaglutide and tirzepatide

Semaglutide is GLP-1 only. It delivers strong appetite suppression but little direct effect on energy expenditure. Tirzepatide adds GIP, which improves nutrient handling and often enhances weight loss compared to semaglutide. Retatrutide adds glucagon receptor activity on top of GLP-1 and GIP. That third pathway appears to raise energy use slightly and can deepen fat loss, but it also calls for tighter dose control and monitoring.

Training and nutrition basics while on retatrutide

• Keep resistance training consistent with progressive overload where possible.
• Target around 2.0 g of protein per kilogram bodyweight each day.
• Avoid very low calorie extremes that risk muscle loss and fatigue.
• Do not stack with stimulant-heavy fat burners. This increases cardiovascular strain.
• Plan a taper at the end to control appetite rebound.

20-week retatrutide cutting protocol

For harm reduction and education. Not medical advice. Use only under qualified medical supervision.

Retatrutide is investigational. It is not licensed by the MHRA or the FDA and no new drug application has been filed, so there is no prescribing guidance to follow. What follows is anchored on the doses the trials actually used, and it stops where the published tolerability data stop supporting it.

Once-weekly subcutaneous dosing. Increase only when side effects are mild and stable for at least two weeks. Hold a dose longer if nausea or fatigue persist. Hydration, electrolytes, protein intake and resistance training are non-negotiable.

Week 1–2 — Optional low start

1 mg once weekly. This step is more cautious than the trial schedule rather than part of it: phase 3 began at 2 mg, and 1 mg appears in phase 2 only as a fixed low-dose arm. It costs two weeks and gives you a read on tolerance before the first real rung. Skip it if you would rather follow the trial schedule exactly.

Week 3–6 — Initiation

2 mg once weekly. This is the dose every phase 3 participant started on. Keep calories moderate. Expect GI symptoms to be most noticeable here. Do not escalate early.

Week 7–10 — First increase

4 mg once weekly if tolerated. One step up, which is exactly how the lowest phase 3 arm reached its target. Appetite suppression should be clear now. Maintain training intensity. If side effects linger, drop back to 2 mg until they settle.

Week 11–16 — Maintenance

Hold 4 mg once weekly. This is a complete trial arm rather than a staging post: in TRIUMPH-1, 4 mg produced an average weight reduction of 19.0% at 80 weeks, with 4.1% of participants stopping because of side effects against 4.9% on placebo. Fewer people came off it than came off nothing. Check glucose, electrolytes and liver enzymes during this block.

Week 17–20 — Taper and off

Step down to 2 mg for two weeks, then stop. Tapering reduces rebound hunger and helps digestion normalise. Keep protein high and training steady during the exit.

Why this stops at 4 mg

The higher doses work better and are tolerated worse, and the gap widens quickly. TRIUMPH-1 reported average reductions of 19.0% at 4 mg, 25.9% at 9 mg and 28.3% at 12 mg, while discontinuation for side effects ran 4.1%, 6.9% and 11.3% across the same three arms. Dysesthesia and urinary tract infections clustered at the top doses. The target doses studied in phase 3 were 4 mg, 9 mg and 12 mg, so above 4 mg the next figure with trial data behind it is 9 mg. Intermediate numbers such as 5 mg or 7 mg are not doses anybody has published data on.

Practical takeaways

• Start low and go slow. Dose jumps create most problems.
• Baseline bloods before the first dose, then every four to six weeks. Add checks sooner if symptoms change.
• Do not mix with heavy stimulants. It adds unnecessary risk.
• Plan the end from the start. Tapering beats a hard stop.
• If in doubt, hold the dose and review rather than pushing higher.

Retatrutide may be more powerful than semaglutide and tirzepatide for fat loss. That power demands discipline. With structure and monitoring it can support a controlled cut with less hunger. Without those safeguards it can turn a tidy plan into a risky experiment.

Disclaimer: Retatrutide is not approved for bodybuilding or athletic enhancement. This article is for information and harm reduction only and does not replace medical advice.