Retatrutide dosing: what we know so far

Retatrutide is a new injectable medication for weight loss and type 2 diabetes still being researched and developed by Eli Lilly. Currently, there’s no official retatrutide dosing information because the medication hasn’t been approved yet by the United States Food and Drug Administration (FDA) and is not yet commercially available.

Still, this drug is causing a lot of excitement because it packs a triple punch, acting on three different hormone receptors: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon. If you’re curious about what to expect about dosing for retatrutide, you’re certainly not alone. 

Below, we share everything we know about retatrutide dosage: the likely starting dose of retatrutide, the retatrutide dosage schedule used in clinical trials so far, a retatrutide dosing chart, and more.

Currently, there’s no official retatrutide dosage for weight loss because the medication isn’t FDA-approved yet. But here’s what we know from clinical trials so far.

Clinical trial doses have ranged from 1 mg to 12 mg injected once weekly. The phase 3 program is studying maintenance doses of 4 mg, 9 mg, or 12 mg. Here’s how retatrutide dosing has worked in clinical trials:

• Starting dosage: Participants started at 2 mg once weekly for the first four weeks. Like tirzepatide dosing for weight loss, this low starting dose gives the body a chance to adjust to the medication before moving to higher doses.

• Step-up dosages: Participants then increased their dose strength every 4 weeks, first to 4 mg, then 6 mg, then 9 mg, then 12 mg, depending on their assigned maintenance dose. 

• Maintenance dosage: Clinical trials have studied maintenance doses of 4 mg, 9 mg, and 12 mg once weekly. 

• Maximum dosage: The maximum dosage studied is 12 mg once weekly. After about 80 weeks, Eli LIlly has reported that people taking this max dose lost about 28% of their body weight on average. 

Remember, some of the results reported by Eli Lilly have not been published in the medical literature yet. Also, any information on retatrutide dosing for weight loss is based on current data, but research is ongoing and FDA approval is pending.

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Retatrutide is a once-weekly injection. Once approved by the FDA, it will likely follow a gradual dose step-up schedule, with dose increases every 4 weeks — similar to other weight-loss injections.

Retatrutide dosing schedules have varied slightly between clinical trials. Phase 2 trials included 8 mg doses. Phase 3 trials swapped out the 8 mg dose for 6 mg and 9 mg doses based on the phase 2 data. Doing this also lengthened the step-up timeline. 

The following is the retatrutide dosage schedule used in Phase 3 trials for participants who reached the maximum dose. This schedule may change once the FDA reviews the final data. 

Like many other weight loss medications, in general, the higher the retatrutide dose, the greater the body weight reduction.

• In a Phase 2 clinical trial, adults with overweight or obesity taking the lowest dose (1 mg) lost about 8.7% of their body weight on average after 48 weeks. These average results increased at higher doses: about 17.1% at the 4 mg dose, 22.8% at the 8 mg dose, and 24.2% at the 12 mg dose. Those who took a placebo lost just 2.1% of their body weight.

• In the 68-week Phase 3 TRIUMPH-4 trial, adults with obesity and at least one weight-related medical problem who took 9 mg of retatrutide lost an average of about 26% body weight, while those taking 12 mg retatrutide lost an average of nearly 29%. The placebo group experienced an average weight loss of 2.1%. 

• In the Phase 3 TRIUMPH-1 trial, adults with overweight or obesity who took just 4 mg of retatrutide for 80 weeks lost 19% of their starting body weight. The 12 mg group lost an average of about 28%, while the placebo group lost 2%. 

There are some dosing considerations and side effects to keep in mind if you’re considering retatrutide for yourself. (Right now the only way to get retatrutide is through a clinical trial). 

• Initiation. While clinical trials of retatrutide have used different starting doses, FDA-approved injections (like Zepbound or Wegovy) have standardized starting doses. If retatrutide is approved, your provider will likely prescribe the standard initiation dose, whatever that winds up being.

• Side effects and individual response. Retatrutide sIde effects like nausea, diarrhea, and constipation are more common at higher doses and tend to occur mainly during the dose-escalation period. If gastrointestinal symptoms are interfering with daily life, your prescriber might pause or slow your dose escalation schedule.

• Dose limits: Even in clinical trials, not everyone can tolerate — or needs — a 12 mg retatrutide dose each week. Plus, people have lost significant weight even on lower doses like 4 mg and 9 mg. Sometimes, people even have their dose reduced because they lost enough weight.

• Discontinuation scenarios: Retatrutide still isn’t FDA-approved or commercially available. But based on similar GLP-1s, it will likely have some safety warnings related to conditions like pancreatitis and gallbladder problems. If your situation changes (e.g., if you get pregnant or develop a serious side effect), you might be told to discontinue retatrutide.

You can’t take retatrutide for weight loss just yet — not until (and unless) it gets FDA approval. But if it does get approved, retatrutide is being studied as a weekly subcutaneous injection. Meaning, it will likely be taken by giving yourself a shot. 

There are several injectable weight loss medications on the market now so there’s a good chance injecting retatrutide will follow similar steps. For example, Zepbound is another once-weekly weight loss injection. Here’s how retatrutide might be taken, based on instructions for how to take Zepbound:

1. Take retatrutide once weekly. Take it on the same day each week. The time of day is flexible, and the medication can be taken with or without food. This keeps the medication steady in your system.

2. Wash your hands first. Use soap and running water, then dry off with a paper towel or unused cloth towel. These simple steps help prevent infection.

3. Choose and clean the injection site. Subcutaneous injections like retatrutide and Zepbound are given in the thigh or abdomen. The back of the upper arm is also an option, but only if someone else is giving you the injection. Before giving yourself a shot, clean the area with an alcohol swab. Rotate injection sites with each dose. 

4. Inject the medication. In clinical trials, retatrutide has been administered using syringes or multidose prefilled pens (Kwikpens). Regardless of the delivery system, inject straight into the skin at a 90-degree angle. 

5. Safely dispose of injector pens or needles. Used pens and needles should be placed in an FDA-cleared sharps container or a heavy-duty plastic container with a secure lid (such as a laundry detergent bottle). Definitely do not put your used pens and needles directly in your kitchen or household trash.

6. If you miss a dose, follow the instructions. Based on similar medications like Zepbound, if you miss a dose, you may be instructed to take it as soon as possible within 4 days. If more than 4 days have passed, skip the missed dose and take your next dose on the regularly scheduled day. Always follow your healthcare provider’s specific instructions for dosing your medication.

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Retatrutide is an investigational drug being developed by Eli Lilly in late-stage development. Because it is still being studied, dosing has not been finalized. Official retatrutide dosage guidance will be determined if and when the FDA approves the medication.

Here’s what we know about retatrutide dosing:

• Retatrutide starts low and increases slowly. In clinical trials, the dosage has started at 1 mg or 2 mg, then increased every 4 weeks until a maintenance dose of 4 mg, 9 mg, or 12 mg is reached.

• It’s injected once weekly. Similar to injectable tirzepatide or injectable semaglutide,  retatrutide is injected under the skin on the same day each week.

• Higher dose strengths cause more weight loss. Clinical trials have shown participants lose more weight on average at higher doses. 

• Retatrutide is still being studied. Even if the FDA eventually approves it, there’s no guarantee that the official retatrutide dosage will match the dosage used in the latest clinical trial.