Library / Peptides / Weight Management / Retatrutide

Emerging evidence · Grade B

Retatrutide

Retatrutide (LY3437943)

Score

68 / 100

Class

Triple agonist · GLP-1 / GIP / glucagon

Sponsor

Eli Lilly

Phase

III · TRIUMPH

TL;DR

Eli Lilly's investigational triple agonist (GLP-1 + GIP + glucagon) — the first in its class to reach late-stage development.

Phase 2 readout in NEJM 2023 reported mean weight loss of ~24% at 48 weeks with the 12 mg dose, the largest effect ever published for an incretin-class agent.

Not FDA-approved and not legitimately available outside of the TRIUMPH Phase 3 program. Any retail or compounded 'retatrutide' is gray-market with no quality assurance.

The glucagon-receptor arm adds energy expenditure — and a dose-dependent increase in resting heart rate (roughly 5–10 bpm) that distinguishes it from pure GLP-1 or GLP-1/GIP agents.

Wt loss (ph. 2, 12 mg)

−24.2%

NEJM 2023 · 48 wk

≥30% responders

~26%

12 mg arm · ph. 2

HbA1c drop (T2D, ph. 2)

−2.0%

highest dose · 36 wk

Liver fat (MASLD)

−80%+

MRI-PDFF · sub-study

Resting HR

+5–10 bpm

dose-dependent

Part 01 · How it works

Mechanism.

Retatrutide is a single designed peptide that activates three different metabolic receptors at once: GLP-1 (reduces appetite and improves insulin release), GIP (adds a second incretin signal and modulates fat storage), and glucagon (turns up the body's energy expenditure by pushing the liver and fat tissue to burn stored fuel). The result is a molecule that lowers calories in and raises calories out from the same injection.

Semaglutide closes the fridge. Tirzepatide closes the fridge and tunes up your metabolism. Retatrutide closes the fridge, tunes up metabolism, and also turns on the furnace — all from one weekly shot.

GLP-1R agonism

Activates GLP-1 receptors on pancreatic β-cells and CNS satiety centers — glucose-dependent insulin secretion, delayed gastric emptying, appetite suppression.

GIPR agonism

Activates GIP receptors on β-cells and adipose tissue — amplifies incretin effect and modulates lipid handling; contributes to weight loss beyond what GLP-1 alone achieves.

Glucagon-R agonism

Balanced partial glucagon agonism on hepatocytes — drives hepatic fatty-acid oxidation and thermogenesis without breaking glycemic control, which GLP-1/GIP co-agonism offsets.

Half-life engineering

Fatty-acid conjugation supports reversible albumin binding; once-weekly subcutaneous dosing with multi-day exposure.

HR / sympathetic tone

Glucagon-R activation raises cAMP in cardiac tissue — the most plausible explanation for the dose-dependent ~5–10 bpm rise in resting heart rate observed in Phase 2.

Part 02 · Dosing & administration

How it's taken.

Values below describe how Retatrutide has been administered in published trials and labeling. Provided for educational purposes only — this is not medical advice and not instructions for self-administration. Consult your healthcare provider before making any health decision.

Wk 1–4

2 mg

Starter — minimize GI titration effects

Wk 5–8

4 mg

First step up

Wk 9–12

8 mg

Second step up

TARGET

Wk 13+

12 mg

Highest studied dose · Phase 2 efficacy arm

Phase 2 regimen shown above — investigational only. No approved dosing exists.

Trial protocols required 4-week intervals between dose increases; faster titration increases GI adverse events.

Heart rate was monitored at every visit in the Phase 2 program; expect similar monitoring in any legitimate trial.

Need help with reconstitution?

Use the free peptide calculator for dilution, unit conversion, and injection volume.

Open calculator

Part 03 · Safety

Side effects, rare serious events, who shouldn't.

Common

Nausea

Class effect; peaks in first 8 weeks of titration.

35–45%

Diarrhea

Usually transient; hydrate.

20–30%

Vomiting

Dose-limiting for some; titrate slower if needed.

15–25%

Constipation

Manage with fiber and hydration.

10–15%

Decreased appetite

Part of the intended effect; watch in underweight or elderly.

25–35%

Serious · rare

Pancreatitis

Class concern inherited from GLP-1 agents.

<1%

Cholelithiasis (gallstones)

Rapid weight loss is itself a risk factor.

~2%

Resting HR elevation

Small (5–10 bpm) but near-universal at high doses; long-term CV implications unknown.

~100%

Thyroid C-cell tumors

Inherited class caution from GLP-1 arm.

Rodent signal

Severe GI / gastroparesis

Emerging class signal; retatrutide-specific incidence not yet published.

<1%

Absolute · do not use

Personal or family history of medullary thyroid carcinoma (class caution inherited from GLP-1 agents)

Multiple endocrine neoplasia syndrome type 2 (MEN2) (class caution)

Known hypersensitivity to retatrutide or any component

History of pancreatitis

Pregnancy or breastfeeding

Severe gastrointestinal disease (gastroparesis)

Use outside of a clinical trial (retatrutide is not approved; there is no legitimate prescription or supply chain)

Relative · discuss first

Baseline elevated resting heart rate or tachyarrhythmia — discuss before any trial enrollment

Active cardiovascular disease with rate-sensitive conditions

History of pancreatitis — proceed only with GI / endocrine input

Severe gastroparesis at baseline

Active eating disorder — complex risk/benefit at 24%+ weight loss magnitudes

Any attempt to source retatrutide outside of a registered Lilly clinical trial — no legitimate supply chain exists

Interactions

Insulin

As with other incretin agents, expected increased risk of hypoglycemia when co-administered; trial protocols typically adjust insulin doses at initiation

Major

Sulfonylureas

Expected additive hypoglycemia risk; trial protocols adjust doses

Major

Oral medications with narrow therapeutic index (warfarin, digoxin, levothyroxine)

Delayed gastric emptying (incretin class effect) may alter absorption of oral drugs; trial protocols monitor levels

Moderate

Oral hormonal contraceptives

Delayed gastric emptying may reduce absorption during titration; non-oral contraception or careful timing is generally advised

Moderate

Beta-blockers and rate-controlling agents

Retatrutide's glucagon-receptor component has been associated with modest resting heart rate elevation; potential interaction with agents used to control heart rate should be assessed clinically

Moderate

Labs to monitor

HbA1c

Per trial protocol (typically baseline and every 3 months)

Glycemic efficacy marker; particularly relevant in T2D trial arms

Fasting Glucose & Insulin

Per trial protocol

Track glycemic parameters during titration

Lipase & Amylase

Baseline and if symptomatic

Pancreatitis surveillance (incretin-class concern)

CMP (Comprehensive Metabolic Panel)

Baseline and every 3 months

Hepatic transaminases can shift with glucagon-receptor agonism; also renal and electrolyte safety

Lipid Panel

Baseline and every 3–6 months

Track triglycerides and atherogenic markers; glucagon component may influence lipid handling

Resting Heart Rate & Blood Pressure

Every visit during titration

Glucagon-receptor activation has been associated with a modest increase in heart rate in Phase 2 trials

Thyroid Panel (TSH, Free T4)

Baseline and every 6–12 months

Incretin-class thyroid C-cell concern inherited from the GLP-1 arm

Part 04 · Evidence

How strong is the evidence?

Grade B

Grade B. The Phase 2 effect size is arguably the most striking ever reported for an injectable obesity drug — but it is still Phase 2, with all that implies for durability, rare events, and real-world performance. Treat as highly promising, not settled.

Mechanistic plausibility

Extends well-mapped GLP-1/GIP biology with a third, pharmacologically coherent glucagon arm.

Animal data

Preclinical models consistently show greater weight and liver-fat effects than dual or single agonists.

Human trial quality

Well-designed Phase 2 RCTs (obesity, T2D, MASLD sub-study); Phase 3 TRIUMPH still accruing.

Replication

Phase 2 findings not yet independently replicated outside Lilly's program.

Safety signal

GI profile similar to GLP-1 class; glucagon-driven HR increase is a novel, still-uncharacterized signal.

Long-term data

Longest published follow-up is 48 weeks; post-discontinuation regain and multi-year safety unknown.

Part 05 · Research log

Every study we cite.

We list each study with its methodology, funding source, and our quality grade. Flagged studies aren't dismissed — they're tagged so you can weigh them.

2023

New England Journal of Medicine Industry funded

Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial

At 48 weeks, the 12 mg dose produced −24.2% mean body weight vs −2.1% placebo. About 26% of 12 mg participants achieved ≥30% weight loss.

RCT, 48 wk, placebo-controlled · n = 338 · Funded by Eli Lilly. Phase 2 sample size. Durability beyond 48 weeks and regain after discontinuation not characterized in primary publication.

High

2023

The Lancet Industry funded

Retatrutide, a GLP-1 / GIP / glucagon receptor agonist, in adults with type 2 diabetes — Phase 2

Dose-dependent HbA1c reductions exceeding 2 percentage points at the highest dose, with substantial co-benefits in body weight.

RCT, 36 wk, active + placebo comparator · n = 281 · Sponsor-designed and analyzed. Active comparator dosing may not represent optimal practice.

High

2024

Nature Medicine Industry funded

Retatrutide and hepatic fat in participants with MASLD — Phase 2 sub-study

Highest-dose arm showed median liver fat reduction >80% by MRI-PDFF; non-invasive fibrosis markers improved.

Sub-study of Phase 2 obesity trial, 48 wk · n = 98 · Small sub-study; surrogate (imaging) endpoints rather than biopsy confirmation in most participants.

Moderate-High

2024

Pooled Phase 2 analysis Industry funded

Resting heart rate and autonomic effects of retatrutide across doses

Dose-dependent increase in resting heart rate of roughly 5–10 bpm at highest doses, stable across treatment period; no excess arrhythmia signal reported.

Post-hoc pooled analysis · n = 619 · Post-hoc pooling; cardiovascular outcomes underpowered at Phase 2 scale.

Moderate

2025

ClinicalTrials.gov registry / investor materials Preliminary

TRIUMPH Phase 3 program — design and ongoing trials

Phase 3 readouts staggered from late 2026 through 2027; primary obesity readout expected first. No efficacy data published yet.

Phase 3 program — obesity (TRIUMPH-1 through -4), T2D, MASH, OSA, knee OA · Not yet peer-reviewed; interpret any interim signals cautiously.

N/A

Part 06 · Cost & access

Where it's available, at what price.

United States

Investigational

Available only through Eli Lilly's TRIUMPH Phase 3 program. Search ClinicalTrials.gov for enrolling sites.

No cost within a trial

European Union

Investigational

Trial sites across multiple EU countries under TRIUMPH program.

No cost within a trial

United Kingdom

Investigational

Select UK trial sites within TRIUMPH.

No cost within a trial

Canada · Australia · Japan

Investigational

Limited trial presence; check national registries.

No cost within a trial

Gray-market / compounded

Not available

We strongly advise against. No legitimately manufactured retatrutide exists outside of Lilly's trial supply. Any 'retatrutide' sold retail is of unverifiable origin.

N/A

The Peptide Column takes no affiliate commission from any source. For retatrutide specifically, the only legitimate access route is a registered clinical trial — we will not link to any other source.

Part 07 · Your appointment

Questions to bring.

Is retatrutide available to me through a clinical trial, and am I eligible to enroll?

Given that retatrutide is not FDA-approved, what approved options (semaglutide, tirzepatide) should I consider first?

How do the glucagon-receptor effects — including possible heart rate increase — apply to my cardiovascular history?

What monitoring would be appropriate if I participate in a retatrutide trial?

Retatrutide

Mechanism.

How it's taken.

Side effects, rare serious events, who shouldn't.

How strong is the evidence?

Every study we cite.

Where it's available, at what price.

Questions to bring.

Further reading.