Retatrutide

Retatrutide is a GIP-analogue backbone carrying a fatty-diacid for albumin binding, engineered for balanced potency across three receptors. The GLP-1 and GIP arms do what they do in tirzepatide - satiety, delayed gastric emptying, glucose-dependent insulin release. The glucagon arm is the new variable: hepatic glucagon receptor activation increases resting energy expenditure, mobilises hepatic triglyceride and drives lipolysis, which is why liver-fat reductions of over 80% were seen in phase 2 and why weight loss keeps climbing past the tirzepatide ceiling. The cost of the glucagon arm is a rise in heart rate and a transient worsening of glycaemia at high doses in some people, which is why the dose escalation is unusually slow.

Targets: GIP receptor, GLP-1 receptor, Glucagon receptor

• · Trials started at 2000 mcg weekly and stepped up every 4 weeks toward maintenance doses of 4000, 9000 or 12000 mcg. TRIUMPH-1 gave 17.6% at 4 mg, 23.7% at 9 mg and 25.0% at 12 mg by 80 weeks.
• · Most people self-administering start at 1000-2000 mcg and hold each step for at least 4 weeks. Retatrutide is more stimulating and more nausea-provoking per milligram than tirzepatide, and jumping steps reliably ends in vomiting.

Work out your exact syringe units →

• very commonNausea and vomiting— Dose-escalation-dependent and generally worse than tirzepatide at equivalent weight loss.
• very commonDiarrhoea and constipation
• very commonLoss of lean mass— Weight loss this large makes protein intake and resistance training non-negotiable.
• commonIncreased resting heart rate— Glucagon-driven; typically 5-10 bpm but larger rises have been reported at 12 mg.
• uncommonCutaneous hyperesthesia or skin sensitivity— A distinctive dose-dependent signal seen in phase 2 that is not typical of other incretins.
• uncommonTransient rise in fasting glucose at high doses— Glucagon-receptor effect; usually resolves with continued weight loss.

• Personal or family history of medullary thyroid carcinoma or MEN2 - the same C-cell signal applies to the class.
• History of pancreatitis.
• Pregnancy.
• Uncontrolled tachyarrhythmia - the glucagon arm raises heart rate.
• Type 1 diabetes without close supervision - the glucagon component complicates glycaemic control.

• redundantsemaglutide — Retatrutide already contains full GLP-1 agonism.
• redundanttirzepatide — Overlapping GIP and GLP-1 agonism; stacking only stacks side effects.
• cautioninsulin-analogues — Complex - the incretin arms lower glucose while the glucagon arm can raise it. Monitor closely.
• synergycagrilintide — Anecdotally added for extra satiety and lean-mass preservation; no trial data for this combination.

• · Resting heart rate daily during escalation.
• · Fasting glucose and HbA1c, especially in the first 12 weeks.
• · Liver enzymes and, where available, liver fat by MRI-PDFF if the goal is MASLD.
• · Body composition every 3-4 months.
• · Weight and waist weekly.

Investigational. Not approved in any jurisdiction as of mid-2026; sold only as a research chemical, with no pharmaceutical-grade consumer supply.

• Jastreboff et al. 2023, retatrutide phase 2 obesity trial, NEJM (trial)
• Rosenstock et al. 2023, retatrutide phase 2 in type 2 diabetes, The Lancet (trial)
• Eli Lilly 2026, TRIUMPH-1 phase 3 topline results (trial)
• Eli Lilly 2025, TRIUMPH-4 phase 3 in obesity with knee osteoarthritis (trial)

The interesting part of retatrutide is the glucagon receptor arm, because it is the only mechanism in this entire class that raises energy expenditure rather than only lowering intake. Hepatic GCGR is Gs-coupled; activation raises cAMP, drives PKA-mediated phosphorylation of hormone-sensitive lipase and increases fatty-acid oxidation and hepatic glucose output. Two consequences follow directly. The good one is that hepatic triglyceride content collapses - phase 2 showed over 80% relative reduction in liver fat by 48 weeks, which is larger and faster than pure incretins achieve, and it happens partly independent of weight. The bad one is that hepatic glucose output rises, which is why fasting glucose can drift upward at 12 mg in people without diabetes early in treatment before weight loss overtakes it. The GLP-1 arm is what keeps that from becoming clinically meaningful hyperglycaemia; the whole molecule is a balancing act between an arm that raises glucose and two arms that lower it. The heart-rate rise of 5-10 bpm is also glucagon-mediated, through direct chronotropic GCGR signalling in the heart plus increased sympathetic tone from raised energy expenditure, and it is dose-dependent - it is the main reason escalation is slower than with tirzepatide. The cutaneous hyperesthesia reported in phase 2 is genuinely unexplained and is not a known class effect; it did not appear in the tirzepatide programme. Whether retatrutide's advantage over tirzepatide is mostly the glucagon arm or mostly that its GLP-1 and GIP potencies are simply higher has not been separated experimentally.

Escalating on the tirzepatide schedule. Retatrutide is more emetogenic per milligram and the glucagon arm adds a cardiovascular dimension that tirzepatide does not have, so people who go up every four weeks by habit end up vomiting at 8 mg with a resting heart rate of 105. Second, ignoring the fasting glucose rise and concluding the drug 'gave them diabetes' - it is a known transient glucagon-receptor effect that usually resolves, but it needs watching rather than panic or denial. Third, product quality. Retatrutide has no pharmaceutical-grade consumer supply at all, purity varies enormously between grey-market suppliers, and third-party HPLC and mass-spec testing is the only way to know what is in the vial. Fourth, weight loss this fast without a training and protein plan produces a body composition outcome people are not happy with even when the scale number is spectacular. Fifth, the cutaneous hyperesthesia - a burning or hypersensitive skin sensation - is real, dose-dependent and unexplained, and people frequently mistake it for a neuropathy or an allergic reaction.

1. 2 mgWeeks 1-4 — Phase 3 starting dose. People self-administering commonly start at 1000 mcg instead, which is defensible given how nausea-provoking this molecule is per milligram.
2. 4 mgWeeks 5-8 — TRIUMPH-1 maintenance dose for the lowest arm, which still gave about 17.6% at 80 weeks. Many people should simply stop here.
3. 6 mgWeeks 9-16 — Intermediate step. Watch resting heart rate more than the scale through this window.
4. 9 mgWeeks 17-24 — About 23.7% at 80 weeks in TRIUMPH-1. The tolerability cost starts to be obvious.
5. 12 mgWeek 25 onward — Top studied dose, about 25.0% at 80 weeks. The extra 1.3 percentage points over 9 mg buys a lot of nausea and tachycardia.

• Glucagon receptor (GCGR) — Not reliably published; described as near-balanced with the incretin arms

  Increased resting energy expenditure, hepatic lipolysis and fatty-acid oxidation, dramatic liver-fat reduction, and the dose-dependent rise in heart rate and fasting glucose.

• GLP-1 receptor (GLP1R) — Not reliably published

  Satiety, delayed gastric emptying, glucose-dependent insulin secretion. Also the counterweight to the glucagon arm's hyperglycaemic push.

• GIP receptor (GIPR) — Not reliably published

  Insulin sensitisation, adipose lipid buffering, and probable central anti-emetic contribution.

• Retatrutide phase 2 obesity trial Phase 2 · n=338 · 48 weeks · 2023

  Mean weight reduction of 24.2% at 12 mg weekly versus 2.1% for placebo, with no plateau by week 48.

• Retatrutide phase 2 in type 2 diabetes Phase 2 · n=281 · 36 weeks · 2023

  HbA1c reduction up to about 2.0% with dose-dependent weight loss, against placebo and dulaglutide comparators.

• TRANSCEND-T2D-1 Phase 3 · 2026

  Glycaemic efficacy and safety of retatrutide in people with type 2 diabetes inadequately controlled with diet and exercise.

• TRIUMPH-1 Phase 3 · 80 weeks · 2026

  Reported by the sponsor as 17.6% at 4 mg, 23.7% at 9 mg and 25.0% at 12 mg at 80 weeks, continuing to about 30% at 104 weeks. This is company-reported and was not confirmed against a peer-reviewed publication in this session.

Weeks 1-2: appetite suppression, often more abrupt than tirzepatide. Weeks 2-6: heart rate climbs and settles at a new baseline; nausea peaks after each step. Week 4: approximate steady state. Weeks 4-12: fasting glucose may drift up before turning around. Weeks 8-24: liver fat falls steeply - this is the fastest-moving endpoint on the drug. Weeks 48-104: weight loss was still accruing at 48 weeks in phase 2 and reportedly continued through 104 weeks in phase 3, which is unusual and is the main reason this compound is interesting.

Retatrutide already contains full GLP-1 and GIP agonism, so semaglutide, tirzepatide, VK2735 and every other incretin is redundant. Cagrilintide is the combination people talk about, on the theory that amylin adds satiety through a separate receptor and helps preserve lean mass - there is no trial evidence for that pairing and you would be layering an unapproved research chemical on top of another unapproved research chemical. If you are going to run retatrutide at all, the things that actually matter alongside it are a heart-rate monitor, potassium and magnesium repletion, 2 g/kg protein and hard resistance training. Beta-blockade to mask the tachycardia is a bad idea - the heart rate is the signal telling you the dose is too high.

Against tirzepatide: higher reported weight loss, worse tolerability, added tachycardia and transient hyperglycaemia, and no approval anywhere. Tirzepatide is a licensed drug with a supply chain; retatrutide is a research chemical with better numbers. Against survodutide: both carry a glucagon arm, but survodutide is glucagon-based with two receptors while retatrutide adds GIP - survodutide has the stronger published liver-fibrosis histology data, retatrutide has the larger weight numbers. Against CagriSema and semaglutide: not close on weight, and not comparable on evidence maturity either. If your goal is specifically liver fat, retatrutide's over-80% reduction in phase 2 is the largest figure in the class, though it comes from a phase 2 imaging endpoint rather than biopsy.

$60–$300/month. Grey market only - there is no legitimate consumer supply anywhere. Typical research-vial pricing runs 60-300 per month equivalent depending on dose and supplier. Third-party purity testing adds roughly 100-200 per batch and is worth it here more than for any other compound in this class. Market observation, not verified pricing.

• ?No published human pharmacokinetic parameters could be verified - volume of distribution, clearance, protein binding and bioavailability are all unpublished or unresolved.
• ?The TRIUMPH-1 phase 3 weight-loss figures quoted in the Core record are company communications; no peer-reviewed TRIUMPH-1 publication could be resolved in this session.
• ?Receptor binding affinities at all three targets are not reliably published.
• ?The cause of the cutaneous hyperesthesia signal is unknown.
• ?It is not established whether retatrutide's advantage over tirzepatide comes from the glucagon arm or simply from higher incretin potency.
• ?Long-term cardiovascular safety of chronic glucagon-receptor agonism in humans is entirely uncharacterised - the heart-rate rise is real and its consequences over years are unknown.
• ?Cost figures are market observations, not verified pricing.

• Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial Jastreboff AM et al., N Engl J Med, 2023 · PMID 37366315

  The 24.2% at 48 weeks result, and the source of the heart-rate, hyperesthesia and fasting-glucose signals.

• Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA Rosenstock J et al., Lancet, 2023 · PMID 37385280

  The diabetes phase 2, where the glucagon-arm glycaemic trade-off is easiest to see.

• Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1) Bajaj HS et al., Lancet, 2026 · PMID 42250575

  The first peer-reviewed retatrutide phase 3 outcome that could be resolved in this session.