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.

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. GLP-1 also lowers the amount of new glucose (sugar) that your liver makes. What’s more, GLP-1 slows digestion to help you feel fuller. And both hormones target areas of your brain that regulate appetite and influence food cravings.

Glucagon is the hormone that tells your 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 sugar levels 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

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 28% weight loss in studies

Initial results from a phase 3 clinical trial suggest that retatrutide could have significant weight-loss benefits. People reported an average weight loss of about 28% (about 70 lbs) after using retatrutide for 80 weeks (about 18 months) with the highest dose (12 mg). That’s more than any of the approved weight-loss medications.

Results were similar in another phase 3 trial that looked at people with osteoarthritis of the knee who were also considered obese. Participants lost an average of nearly 29% of their starting body weight (about 71 lbs) after using retatrutide 12 mg for 68 weeks (about 15.5 months). They also experienced significant arthritis pain relief and improved physical function.

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

• Chronic lower back pain 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

• Constipation

People using retatrutide also reported a smaller appetite and dysesthesia. Dysesthesia is an unusual or unpleasant skin sensation, such as tingling or stinging. But it’s unclear if retatrutide directly causes this. Rapid weight loss (regardless of medication use) can also cause dysesthesia.

Study participants rated 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 2027

Because phase 3 trials of retatrutide are completed, Eli Lilly can apply for FDA approval. They haven’t done this yet. But with other phase 3 trials set to wrap up during 2026, the manufacturer will likely apply soon. 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 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 or “grey market” 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, or other impurities.

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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