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Molecule library

Retatrutide

Reta · R3

LY3437943

Retatrutide is also often called "Reta" or "R3" in communities and on social media. Here these terms refer to the same molecule: LY3437943.

Triple agonist: GIP + GLP-1 + glucagonPhase III — experimental moleculeNot approved as a medicine to date

Retatrutide is studied mainly for obesity and the metabolic diseases associated with it. It acts on three systems involved in particular in hunger, blood sugar control and energy use.

up to −28.3%Average weight loss reported at 80 weeksPhase III — TRIUMPH-1 — 2026Advanced human data
≈ −86%Liver fatPhase II — MASLD sub-study — 48 weeksHuman data still being explored
Visceral fatSubstantial reduction observedDeep fat located around the organsHuman data still being explored
3 receptorsGIP + GLP-1 + glucagonTriple agonistAdvanced human data

These figures come from different trials, with different populations, doses and durations. They must not be compared directly with one another.

01 · Mechanism

How does it work?

GLP-1

Helps in particular to control hunger and blood sugar.

GIP

Involved in particular in the insulin response and in metabolism.

Glucagon

Involved in managing and using energy.

What makes retatrutide distinctive is that it acts on all three at once.

02 · Landmarks

Understanding the trial phases

Phase I — Explore

What happens when a human being receives this new molecule?

Phase II — Understand

Which doses produce an effect? Which side effects appear?

Phase III — Confirm

Are the results confirmed in far more people before any possible authorisation?

A dose used in Phase I is therefore not automatically a future medical dose. A dose studied in Phase III is not a personal prescription either.

03 · Clinical trials

How doses evolved across the trials

  1. Phase I

    0.1 — 0.3 — 1 — 3 — 4.5 — 6 mg

    Single doses explored. The aim was to study the safety, the tolerability and the behaviour of the molecule in the body.

  2. Phase Ib

    0.5 — 1.5 — 3 mg, with escalations studied up to 6, 9 and 12 mg

    Researchers begin to explore repeated administrations and different dose levels.

  3. Phase II — obesity

    1 — 4 — 8 — 12 mg (target doses studied)

    For some higher-dose groups, starting points of 2 or 4 mg were compared.

  4. Phase III — TRIUMPH programme

    Regimens studied

    Target dose 4 mg2 mg → 4 mg
    Target dose 9 mg2 mg → 4 mg → 6 mg → 9 mg
    Target dose 12 mg2 mg → 4 mg → 6 mg → 9 mg → 12 mg

    Increases were spaced 4 weeks apart in the trials concerned. These are the regimens studied in the clinical trials, not individual recommendations.

Phase II — average weight loss observed at 48 weeks

1 mgabout −8.7%
4 mgabout −17.1%
8 mgabout −22.8%
12 mgabout −24.2%

Source: New England Journal of Medicine — 2023 · NCT04881760.

These values describe study results. They are not individual recommendations.

Phase III trials are today the data closest to a possible future medical use. The final commercial dosage and the presentations of future pens will only be known after the official regulatory decisions.

04 · Clarification

0.5 mg, 1 mg, 2 mg: why do you see everything and its opposite on the Internet?

Low doses were not invented by social media. Some were genuinely explored during the first research phases.

But a dose explored at the start of development does not automatically become a medical protocol.

As the trials progress, researchers select the doses and regimens that will be studied on a larger scale.

That is why you must always look at which phase a dosage comes from before drawing a conclusion.

Social media

You absolutely have to start at 0.5 mg.

Data

0.5 mg was studied in some early trials, but that does not make it a universal rule.

Social media

Starting higher only serves to sell more product.

Data

Clinical trial regimens are defined by the research teams and the development programme, independently of the sellers present on the Internet.

Social media

It did not work for me, so the molecule does not work.

Data

One person's experience cannot determine the general efficacy of a molecule.

PHL takes no side: we simply show the published data.

05 · Results

What the studies observed

Weight

Advanced human data

Phase III TRIUMPH-1: up to −28.3% average weight loss at 80 weeks in the 12 mg group.

About 45% of the participants in this group lost at least 30% of their weight.

Liver fat (MASLD)

Human data still being explored

Phase II — Nature Medicine, 2024. In participants with a large amount of fat in the liver, at 24 weeks:

1 mg−42.9%
4 mgabout −57%
8 mgabout −81%
12 mgabout −82%

At 48 weeks, in the 12 mg group: about −86%.

Steatosis is an excessive accumulation of fat in the liver.

Retatrutide is not an approved treatment for MASLD.

Visceral fat

Human data still being explored

Visceral fat is the deep fat located around the organs. It is different from the fat that can simply be pinched under the skin.

In the small MASLD sub-study, the reduction in visceral fat reached about 48% at 48 weeks in some groups.

This was a small sub-study: this figure does not represent a guaranteed or universal result.

Blood sugar and diabetes

Advanced human data

The studies show that the body controls blood sugar better.

HbA1c reflects the average blood sugar over about three months. The measures followed include blood glucose, HbA1c, insulin and the way the body uses insulin.

The TRIUMPH-2 programme (2026) studied these effects in people living with type 2 diabetes.

4 mgabout −12.7%average weight loss at 80 weeks
9 mgabout −19.1%average weight loss at 80 weeks
12 mgabout −20.8%average weight loss at 80 weeks

HbA1c decreased by up to about 1.6 points depending on the groups studied.

In the Phase II obesity trial, among participants with prediabetes at baseline, about 72% of participants in the retatrutide groups returned to a normal blood sugar range at 48 weeks, compared with about 22% on placebo.

These values describe study results. They are not individual recommendations.

Heart and arteries

Human data still being explored

Certain fat particles in the blood associated with cardiovascular risk decreased.

Among them: ApoB and certain particles carrying cholesterol and triglycerides.

The studies also report a favourable change in certain inflammation markers and an average decrease in blood pressure.

This does not yet prove that retatrutide prevents heart attacks or strokes.

06 · Balance

Blood pressure and heart rate

Blood pressure

An average decrease in blood pressure was observed in some trials.

Retatrutide is not currently an approved treatment for hypertension.

Heart rate

A temporary increase in heart rate was also observed.

07 · Caution

Hormones: a possible indirect effect

Body fat is not only an energy reserve. It also takes part in certain hormonal balances.

A large decrease in visceral fat and an improvement in metabolism may possibly improve indirectly certain imbalances associated with obesity.

Hypothesis — not demonstrated

Not demonstrated: retatrutide is not a hormone treatment, and it has not been demonstrated that it directly improves testosterone, oestrogens or the HPTA axis.

08 · Caution

Energy, mood and quality of life

Losing weight, controlling blood sugar better, regaining mobility or sleeping better can improve general well-being in some people.

Hypothesis — not demonstrated

It has not been demonstrated that retatrutide acts directly as a product that improves mood or concentration.

09 · Emerging research

A research avenue, not a cancer treatment

Preclinical — study in mice

A study published in 2025 in npj Metabolic Health and Disease explored the link between obesity, metabolism and tumour development in animals.

Pancreatic cancer

  • — Reduced tumour engraftment
  • — Delayed onset
  • — Slowed growth
  • — Tumour volume markedly lower than the control group under certain conditions

Lung cancer

Preclinical results pointing in the same direction were also observed in lung cancer models.

Researchers believe the effect could be linked to several changes at the same time: less visceral fat, a better metabolic environment and changes in certain immune cells around the tumour.

These results were observed in mice. They do not demonstrate that retatrutide prevents or treats cancer in human beings.

10 · Tolerability

Adverse effects observed

Nausea
Diarrhoea
Vomiting
Constipation
Marked decrease in appetite

Digestive disorders were generally more frequent during dose-increase periods and with the highest doses.

A temporary increase in heart rate was also reported.

11 · Landmark

Level of evidence

Advanced human dataWeight · blood glucose · HbA1c · waist circumference · certain metabolic markers.
Human data still being exploredLiver fat / MASLD · detailed visceral fat · body composition · cardiometabolic inflammation · long-term cardiovascular benefit.
Preclinical — animalPancreatic cancer · lung cancer · certain immune mechanisms.
Hypothesis — not demonstratedIndirect endocrine consequences · direct effects on mood or concentration not established · other effects not yet demonstrated.

This legend answers a single question: is it demonstrated in human beings, or not yet?

12 · Verify

Want to check for yourself?

Only the original publications, ClinicalTrials.gov and the sponsor's official communications are used as sources.

Warning

This page is an educational summary of the research available on retatrutide.

It gives no prescription and does not determine which dose a person should use.

Retatrutide remains an experimental molecule and is not currently approved as a medicine.

The doses shown on this page correspond to the doses used in scientific studies. They are not individual recommendations.

Research Use Only. These products are neither a drug nor a treatment. Trust & Compliance