# Retatrutide: the triple agonist, and where it actually stands

Updated 24 August 2026 · Written by the Penwise team

Retatrutide is the drug people ask about when they have read about what might come after tirzepatide. It acts at three receptors instead of two, its phase 2 results were striking enough to make general news, and it is not an approved medicine anywhere in the world. Both halves of that matter, and the second half tends to get lost in the reporting of the first.

## The status, first

Retatrutide is investigational. It is in phase 3 trials and has not been approved by the FDA, the EMA or any other regulator. There is no licensed product, no approved dosing, no pharmacy supply and no established safety profile at the level required for approval.

That matters practically, because retatrutide is widely discussed in the same breath as Mounjaro and Wegovy, which are licensed medicines dispensed by pharmacies. It is not in that category. The only legitimate routes to it are enrolment in a clinical trial or, eventually, a prescription if and when it is approved.

> Material sold online as retatrutide, including anything labelled for research use only, is not a medicine. It carries no assurance of identity, purity, sterility, concentration or dose accuracy, and Penwise neither supplies it, sources it nor recommends obtaining it. What this page describes is the drug in the published trial literature.

## What a triple agonist is

The classes are easiest understood as a progression, with each generation adding a receptor.

| Generation | Receptors | Examples | Status |
| --- | --- | --- | --- |
| Single | GLP-1 | Semaglutide, liraglutide | Approved |
| Dual | GIP and GLP-1 | Tirzepatide | Approved |
| Triple | GIP, GLP-1 and glucagon | Retatrutide | Investigational |

A larger number of receptors is not automatically better. Each pathway brings its own effects, wanted and unwanted, which is what the trials exist to establish.

The interesting addition is glucagon. Glucagon is usually discussed as the hormone that raises blood glucose, which sounds like the opposite of what a metabolic drug should do. Its receptor agonism also increases energy expenditure, and the design bet behind retatrutide is that combining that with the intake-reducing effects of GIP and GLP-1 acts on both sides of the energy balance at once, with the glucose effect held in check by the other two pathways.

## What the phase 2 data showed

The phase 2 obesity trial published in 2023 is the source of essentially all the attention. At the highest dose, mean weight reduction was around 24% at 48 weeks.

- **~24%**: Mean weight reduction at the highest dose at 48 weeks in phase 2
- **48 weeks**: Trial duration, still climbing at the end
- **Phase 3**: Where the programme is now

Two cautions belong immediately next to that number. It comes from a phase 2 trial, which is smaller and shorter than the trials that support approval, and the curve had not flattened by week 48, so the figure is not a ceiling. Comparing it directly to the 72-week tirzepatide result is not comparing like with like.

The side effect profile reported was dominated by the same gastrointestinal effects as the approved drugs, dose-related in the same way. Increases in heart rate were observed, which is a known feature of this class and a specific thing phase 3 is powered to characterise properly.

## Pharmacokinetics

Retatrutide is a weekly injection with a half-life of roughly six days, which places it between tirzepatide at about five and semaglutide at about seven.

The consequences follow the same arithmetic as the approved drugs. Steady state arrives after roughly four to five half-lives, so about four weeks. The level falls to a bit under half across a seven-day interval, giving a weekly trough shallower than tirzepatide and deeper than semaglutide. And after a last dose it takes about thirty days to clear. The reasoning is worked through in detail on the [tirzepatide](https://penwiseapp.com/en/guides/how-long-does-mounjaro-stay-in-your-system) and [semaglutide](https://penwiseapp.com/en/guides/how-long-does-ozempic-stay-in-your-system) pages, and the same model applies here.

|  | Semaglutide | Retatrutide | Tirzepatide |
| --- | --- | --- | --- |
| Half-life | About 7 days | About 6 days | About 5 days |
| Steady state | 4 to 5 weeks | About 4 weeks | About 4 weeks |
| Effectively cleared | About 5 weeks | About 30 days | About 25 days |
| Weekly trough | Shallowest | Between | Deepest |

Population figures from the published literature. Retatrutide dosing is not established, since that is what phase 3 determines.

## What is still unknown

This is the honest list, and it is the reason approval takes years rather than months.

- **Long-term safety.** Phase 2 ran 48 weeks in a few hundred people. Approval-grade safety comes from thousands over longer periods.
- **Cardiovascular outcomes.** The heart rate increase seen in this class needs proper characterisation, and outcome data is a different thing from a surrogate measure.
- **The dosing schedule.** Where the ladder starts, how large the steps are and where it tops out are exactly what phase 3 establishes.
- **Durability.** Whether the loss holds, and what happens on stopping, are separate questions again. See [what happens when you stop](https://penwiseapp.com/en/guides/what-happens-when-you-stop-a-glp-1).
- **Who it suits.** Comparative data against tirzepatide in the populations that would actually be prescribed it does not exist yet.

## Why Penwise supports it

Penwise models retatrutide with the correct half-life alongside semaglutide, tirzepatide and liraglutide. The reason is straightforward: trial participants keep their own records, and a tracker that silently substituted the wrong half-life would produce a level curve that is simply wrong.

Supporting a medication in the app is a statement about arithmetic, not an endorsement of obtaining it. The same principle applies throughout: the app knows how the pens work and what the numbers are, and the decision about what to take belongs to you and your prescriber. If you are on an approved treatment, the [Mounjaro](https://penwiseapp.com/en/guides/mounjaro-tracker), [Ozempic](https://penwiseapp.com/en/guides/ozempic-tracker), [Wegovy](https://penwiseapp.com/en/guides/wegovy-tracker) and [Zepbound](https://penwiseapp.com/en/guides/zepbound-tracker) pages cover those.

**Correct pharmacokinetics, whatever you are on** Real half-lives for semaglutide, tirzepatide, retatrutide and liraglutide, with everything kept on your phone. Free core tracker, no account.

## Common questions

**Is retatrutide approved?**

No. It is investigational and in phase 3 trials, and it has not been approved by the FDA, the EMA or any other regulator. There is no licensed product and no pharmacy supply, and the only legitimate route to it currently is enrolment in a clinical trial.

**How does retatrutide differ from Mounjaro?**

Tirzepatide acts at two receptors, GIP and GLP-1. Retatrutide adds a third, the glucagon receptor, whose agonism increases energy expenditure. Tirzepatide is an approved medicine; retatrutide is not.

**How much weight did people lose on retatrutide?**

In the phase 2 obesity trial, mean weight reduction at the highest dose was around 24% at 48 weeks, and the curve had not flattened at the end of the trial. Phase 2 results come from smaller and shorter studies than those supporting approval, so the figure should be read as promising rather than settled.

**What is the half-life of retatrutide?**

Roughly six days, between tirzepatide at about five and semaglutide at about seven. That implies steady state after about four weeks, a weekly trough between the two approved drugs, and effective clearance about thirty days after a last dose.

**Can I buy retatrutide online?**

Material sold online, including anything labelled research use only, is not a medicine and carries no assurance of identity, purity, sterility, concentration or dose accuracy. Penwise does not supply, source or recommend obtaining it.

**When will retatrutide be available?**

That depends on the phase 3 programme and on regulators, and no date can be responsibly given. Approval requires long-term safety and outcome data that is still being collected.

## Sources

Every factual claim on this page traces to the product information a regulator publishes, or to a published trial. Links open on the site of whoever issued the document.

- [Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial](https://doi.org/10.1056/NEJMoa2301972), New England Journal of Medicine, 2023
- [Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5)](https://doi.org/10.1056/NEJMoa2416394), New England Journal of Medicine, 2025
- [Mounjaro: EPAR product information](https://www.ema.europa.eu/en/medicines/human/EPAR/mounjaro), European Medicines Agency

Penwise is a tracking and education tool, not a medical device. Nothing on this page is medical advice, a diagnosis or a recommendation to start, stop or change a dose. Dosing decisions belong to you and your clinician. Ozempic, Wegovy, Rybelsus, Saxenda and Victoza are trademarks of Novo Nordisk; Mounjaro, Zepbound and Trulicity are trademarks of Eli Lilly. Penwise is not affiliated with, endorsed by or connected to either company.

## Keep reading

- [How long does Mounjaro stay in your system?](https://penwiseapp.com/en/guides/how-long-does-mounjaro-stay-in-your-system): Tirzepatide has a five-day half-life. Here is what that means week by week, why it takes a month to reach steady state, and where the trough you can feel comes from.
- [How long does Ozempic stay in your system?](https://penwiseapp.com/en/guides/how-long-does-ozempic-stay-in-your-system): Semaglutide has a seven-day half-life, so it clears over about five weeks and doubles on itself before it settles. What that means week by week.
- [Mounjaro vs Wegovy: two weekly injections, two different drugs](https://penwiseapp.com/en/guides/mounjaro-vs-wegovy): Both are weekly, both are for weight, and they are not the same molecule. The head-to-head trial, the dose ladders, the pens and what actually changes for you week to week.
- [What happens when you stop a GLP-1 medication](https://penwiseapp.com/en/guides/what-happens-when-you-stop-a-glp-1): The drug leaves over weeks, not days, and appetite returns as the level falls. What the withdrawal trials actually found, and what to have written down before you stop.