Guide
How GLP-1 weight-loss medications work
GLP-1 medications are prescription medicines that help some adults lose weight by reducing appetite and helping them feel full sooner. The FDA has approved two for long-term weight management, semaglutide (sold as Wegovy) and tirzepatide (sold as Zepbound), for use alongside a reduced-calorie diet and more physical activity.
How they work
GLP-1 is a hormone your gut releases after eating. These medicines copy its effects: they slow how quickly the stomach empties and act on parts of the brain that control appetite. Tirzepatide also copies a second gut hormone, called GIP. Most are given as an injection under the skin once a week, starting at a low dose that's raised over several months.
Who they're approved for
The FDA approved both medicines for adults with:
- a BMI of 30 or higher, or
- a BMI of 27 or higher plus at least one weight-related condition, such as high blood pressure, type 2 diabetes or high cholesterol.
A licensed provider decides whether a medicine is suitable, based on your health history. Check your BMI →
What the studies found
| Medicine | Main studies | Average extra weight lost compared with placebo |
|---|---|---|
| Semaglutide 2.4 mg (Wegovy) | 68 weeks, adults without diabetes | 12.4% of starting weight |
| Tirzepatide 15 mg (Zepbound) | 72 weeks, adults without diabetes | About 18% of starting weight |
Figures from the FDA's approval announcements. Results vary from person to person, and were smaller in people with type 2 diabetes.
Side effects and warnings
The most common side effects are stomach-related: nausea, diarrhea, vomiting, constipation and stomach pain. The FDA's labels also warn about:
- thyroid tumors seen in rats (it's not known whether this happens in people). These medicines shouldn't be used by anyone with a personal or family history of medullary thyroid cancer or MEN 2 syndrome.
- pancreatitis, gallbladder problems, low blood sugar (especially with some diabetes medicines) and kidney problems
Your provider should go through these with you.
Compounded and online versions
The FDA warns that compounded versions of these medicines are not FDA-approved: the agency doesn't review them for safety, quality or effectiveness. It has also found counterfeit products sold online, and reports of people taking the wrong dose. The FDA's advice: get a prescription from a licensed provider and fill it at a state-licensed pharmacy. How to tell if an online provider is legitimate
Cost and coverage
Prices vary widely by medicine, pharmacy and insurance plan, and coverage for weight loss differs between plans. Check with your insurer or pharmacy before you start.
Sources
- FDA approves new drug treatment for chronic weight management, first since 2014 (FDA release, June 2021, via BioSpace)
- FDA approves new medication for chronic weight management — U.S. Food and Drug Administration
- FDA's concerns with unapproved GLP-1 drugs used for weight loss — U.S. Food and Drug Administration