How to Take Retatrutide: Weekly Shots, Dose Steps and Timing

In Lilly's Phase 3 trials, people inject retatrutide under the skin once a week, starting at 2 mg and moving up one step every 4 weeks to a target of 4 mg, 9 mg or 12 mg. If you're asking how to take retatrutide, that schedule is the only one with results behind it. No approved version exists yet, so there's no label with official instructions, and Lilly says retatrutide is "legally available only to participants in Lilly's clinical trials."

As of September 2026, retatrutide is still in Phase 3, and Lilly plans to file for FDA approval in Q1 2027. Where retatrutide data runs out, we use the tirzepatide and semaglutide labels and mark them as class evidence. For the legal routes, see how to get retatrutide.

How to take retatrutide in Lilly's trials

Every Phase 3 trial with published results used the same ladder. People started at 2 mg a week, and every 4 weeks the dose went up one step (2, 4, 6, 9, then 12 mg) until they reached their assigned target, according to Lilly's TRIUMPH-1 release. Someone aiming for 12 mg got their first 12 mg shot in week 17.

Starting low has a measurable payoff. In the Phase 2 obesity trial, 21 of 35 people (60%) who started at 4 mg on the way to 8 mg reported nausea, against 6 of 35 (17.1%) who started at 2 mg, according to the trial's results on ClinicalTrials.gov.

The rest of the basics, with where each answer comes from:

What each dose did is on the retatrutide dosage page.

Mixing a vial before the first dose

Some retatrutide sold outside trials comes as a vial that needs mixing first. In a March 2026 warning letter, the FDA said one online seller's retatrutide required reconstitution and was sold alongside bacteriostatic water for the job. The amount of water you add sets how many milligrams every syringe mark holds from then on. The retatrutide reconstitution guide has a mixing chart by vial size and the units for each trial dose, and the dose calculator does the math for your own vial.

Giving the shot

Lilly's FAQ says that in its trials, retatrutide is taken as a once-weekly subcutaneous injection: into the fat just under the skin, not into muscle. Lilly hasn't published site instructions for it. The Zepbound label for tirzepatide lists the belly, the thigh, or the back of the upper arm if someone else gives the shot, and says to rotate sites with each dose. Needle length and a site-by-site walk-through are on how to inject retatrutide.

Keeping it cold

Lilly hasn't published storage rules for retatrutide, so the closest guide is tirzepatide. The Zepbound label says to keep pens and vials in the fridge at 2 to 8°C (36 to 46°F), never to freeze them, to protect them from heat and light, and it allows single-dose pens or vials out of the fridge up to 30°C (86°F) for 21 days in total. A vial you've mixed yourself is a different product, and nobody has published how long mixed retatrutide stays stable. The details are on retatrutide storage.

Is there a retatrutide pen?

Not one you can get. Lilly ran a device study (NCT06003465) in 57 healthy people comparing 2 devices for injecting retatrutide, with a single dose from each. It finished on February 8, 2024, and as of September 2026 no results are posted.

Any pen sold as retatrutide today isn't Lilly's. In October 2025, the UK's MHRA seized more than 2,000 unlicensed retatrutide and tirzepatide pens waiting to be shipped from a site in Northampton. What's being sold as a reta pen is covered on the retatrutide pen page.

Cloudy or odd-looking vials

The Zepbound label is blunt: don't use it if you see particles or discoloration. With retatrutide from outside a trial, a clear vial doesn't prove much either. In a September 2026 safety alert, Australia's TGA reported testing an unmarked vial sold as retatrutide after a user needed hospital treatment for uncontrollable vomiting and a torn esophagus. It held no retatrutide. It held undeclared semaglutide, at about 8 times the level in approved semaglutide products. In a June 2026 alert, health officials in Victoria linked 6 cases of acute liver injury since January 2026 to products labeled Retatrutide, possibly from a contaminant.

If you're looking at retatrutide for sale online, the one document that says anything about what's inside is a batch-specific third-party test report, and its batch number has to match your vial. Even a good report only covers what the lab tested for. What cloudiness after mixing can mean, and when to throw a vial out, is on the page about cloudy and problem vials.

Can you take retatrutide as a pill?

No. Of the 33 retatrutide records on ClinicalTrials.gov as of September 2026, 32 give it as an injection under the skin, and the 33rd, Lilly's expanded access listing, doesn't name a route. Lilly's own FAQ describes retatrutide only as a once-weekly injection. Lilly's weight-loss pill, Foundayo (orforglipron), is a different drug. What sellers market as oral retatrutide has its own page.

When does retatrutide start working?

In Lilly's first human study, a single injection kept weight down for up to 43 days (Cell Metabolism 2022). In the 12-week Phase 1b trial in people with type 2 diabetes, the group that stepped up to 12 mg lost 8.96 kg more than placebo (Lancet 2022). The averages people quote come after months at a full dose, though, and the Phase 3 ladder keeps everyone on 2 mg and 4 mg for the first 8 weeks.

For people with obesity, the earliest per-dose results in open sources are from week 24 of the Phase 2 trial. These are the arms that started at 2 mg, like the Phase 3 ladder, plus the 1 mg arm, which didn't step up at all:

Source: the trial's ClinicalTrials.gov results (NCT04881760). The figures are model estimates for people while they stayed on the drug, so people who stopped early don't pull them down. Weight kept falling after week 24: the 12 mg group averaged 24.2% by week 48 in the NEJM paper, and Lilly said people hadn't reached a plateau when the trial ended.

Our read: if the first month on 2 mg feels underwhelming, that fits the design. In the Phase 2 trial, dose increases ran until week 12, so by week 24 the 12 mg group had spent only about 12 weeks on its full dose. We couldn't find week-by-week retatrutide weight for the first month in any open source. For how the months after that tend to go, see the retatrutide results timeline.

Missed a dose or need to move your shot day?

Nothing has been published for retatrutide. The two nearest labels don't agree, which tells you these rules depend on the drug:

• Zepbound (tirzepatide): take a missed dose within 4 days (96 hours). After that, skip it and go back to your usual day. You can move your weekly day if at least 3 days (72 hours) separate two doses.
• Wegovy (semaglutide): take the missed dose if the next one is more than 2 days (48 hours) away; otherwise skip it. After 2 or more missed doses in a row, the label says to restart the dose steps at a lower dose.

Our read: retatrutide's half-life of about 6 days falls inside the Zepbound label's 5 to 6 days, while the Wegovy label gives semaglutide about a week, so the Zepbound rule is the nearer comparison. It's still borrowed from another drug, and a gap of 2 weeks or more is worth raising with a doctor before going back to the old dose.

When to stop and get help

In Australia, Victoria's alert gives the Poisons Information Centre on 13 11 26. In a trial, your study team is the first call. The everyday side effects by dose are on retatrutide side effects.