7 Things to Know About Retatrutide for Weight Loss: Dosages, Clinical Trial Results, and More

Weight-loss injections have exploded in popularity in recent years. Medications like Wegovy (semaglutide) and Zepbound (tirzepatide) have been in the spotlight. Considering how well they work, it’s easy to see why.

But there are several other weight-loss medications that scientists are researching. And early studies suggest that some products in development might work better than those already on the market. Retatrutide is one medication in the pipeline that fits this description.

How does retatrutide work for weight loss? And when might it be FDA approved? Let’s discuss seven things you should know about retatrutide.

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1. Retatrutide works differently from other weight-loss medications

Similar to Wegovy and Zepbound, retatrutide acts like natural hormones found in the body. But instead of acting like one or two hormones, retatrutide acts like three:

• Glucose-dependent insulinotropic polypeptide (GIP)

• Glucagon-like peptide-1 (GLP-1)

• Glucagon

GIP and GLP-1 tell your pancreas to release insulin after eating. They also lower the amount of new sugar (glucose) that your liver makes. What’s more, GIP and GLP-1 slow digestion to help you feel fuller. And they target areas of your brain that regulate appetite and influence food cravings.

Glucagon is the hormone that tells our liver to make new sugar. If you’re thinking that this seems counterintuitive, you’re not alone. But retatrutide’s GIP and GLP-1 activity helps keep glucagon in check. This is why the medication doesn’t cause high blood sugar (hyperglycemia).

Glucagon does more than just create new sugar. It also:

• Speeds up your metabolism

• Helps your body break down fat cells for energy

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This added metabolism boost can add to and complement GIP’s and GLP-1’s actions. And that’s why it seems to provide significant weight loss.

If approved, retatrutide will be the first in a new class of medications.

2. Retatrutide has led to a 24% weight loss in studies

Studies suggest that retatrutide could have significant weight-loss benefits. People reported an average weight loss of about 23% and 24% after using retatrutide for 11 months with the two highest doses (8 mg and 12 mg, respectively). That’s more than any of the approved weight-loss medications — and in a shorter amount of time.

Keep in mind that these results are from a phase 2 clinical trial. This is an earlier-stage study that’s conducted in a smaller number of people. An ongoing phase 3 trial will help confirm how effective retatrutide is for weight loss. This study is expected to wrap up in early 2026.

3. Retatrutide is also being studied for other health conditions

Many people are interested in retatrutide for weight loss, but that’s not all scientists are studying it for. That’s because GLP-1 medications have shown proven benefits for heart health, kidney health, obstructive sleep apnea, and more.

Experts are also looking at whether retatrutide can treat:

• Type 2 diabetes

• Metabolic dysfunction-associated steatohepatitis (MASH) — a health condition caused by fat building up in your liver

• Chronic kidney disease

• Cardiovascular risk reduction

• Osteoarthritis of the knee in people with larger bodies

This isn’t surprising when it comes to medications that act like GLP-1. Other GLP-1 medications are also being studied for these conditions and more.

4. If approved, retatrutide will likely be available as a once-weekly injection

In its phase 3 clinical trials, retatrutide is being given as once-weekly injections. This means that’s the dosage we’re likely to see on the market if it’s approved. You would also likely start with a low dose and gradually raise it over several weeks.

This isn’t unusual. Most GLP-1 medications come as injections. And many of them also have once-weekly dosages and similar dose escalation instructions.

Good to know: Retatrutide is being studied by Eli Lilly, the manufacturer of Zepbound and Mounjaro (tirzepatide). If retatrutide is approved, it might use an injection device that’s similar to these other medications.

5. Retatrutide has side effects similar to other GLP-1 medications

So far, studies suggest retatrutide causes side effects that are similar to other GLP-1 medications. These commonly include gastrointestinal side effects, such as:

• Nausea

• Vomiting

• Diarrhea

• Constipation

People rated these retatrutide side effects as mild or moderate. And side effects were more noticeable when people first started the medication. As with other GLP-1 medications, serious side effects were rare.

6. Retatrutide may be approved in 2026 or 2027

Eli Lilly can’t apply for FDA approval until retatrutide’s phase 3 clinical trials are complete. This is expected to happen in early 2026. After a manufacturer applies for approval, the FDA typically reviews it within 6 to 10 months after accepting the application.

Given this timeframe, the FDA could approve retatrutide in 2027. The timing will depend on when the phase 3 trial finishes, when the manufacturer submits an application, and how long the FDA’s review takes.

7. Counterfeit retatrutide is being sold, but it hasn’t been FDA approved for safety or effectiveness

Similar to other popular weight-loss injections, people are illegally selling counterfeit retatrutide. The FDA has warned against obtaining retatrutide this way. The medication hasn’t been fully studied by the manufacturer or reviewed by the FDA.

Using counterfeit medications, especially before approval, carries a number of possible risks. These can include:

• You may receive a product that contains a different medication.

• You may receive a product that contains no medication.

• Unapproved medications may have risks or side effects that experts are unaware of.

• The device you’re using to inject your dose could malfunction and cause injury.

• The product you receive could be contaminated with germs, such as bacteria or fungi.

Compounding pharmacies helped people access GLP-1 injections while those medications were in shortage. And it’s possible that retatrutide may have its own supply issues if it’s approved. But compounding pharmacies shouldn’t be selling unapproved medications. This is illegal.

So while it may seem tempting to purchase retatrutide, it’s not recommended to do so.

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Written by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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