A drug approved by the Food and Drug Administration to treat people with Type 2 diabetes has ignited a craze among social-media influencers, the rich and famous and everyday people alike.Ozempic, made by Novo Nordisk A/S, has gained popularity for its off-label use, helping users drop excess pounds within a matter of months.

Demand has soared for Ozempic as well its sister drug, Wegovy, and Eli Lilly & Co.’s Mounjaro. Ozempic’s main ingredient, known as semaglutide, is in Wegovy, which was approved by the FDA in 2021 to treat obesity. Lilly’s Mounjaro, whose main ingredient is tirzepatide, was approved by the FDA in 2022 to treat diabetes, though it has also been used for weight loss.

Supply for the drugs hasn’t always kept up with demand. Wegovy was in short supply during much of 2022 because of a manufacturing problem, which fueled the demand for alternatives such as Ozempic and Mounjaro, leading to shortages at times for those drugs, too. The shortages have sometimes deprived people with diabetes of their prescription refills. The shortages have eased, and the companies are adding manufacturing capacity. 

Here’s what to know about Ozempic and other drugs like it: 

Ozempic is in a category of medications that work by mimicking the effects of a naturally occurring gut hormone called glucagon-like peptide-1, or GLP-1. Receptors to GLP-1 are found in the pancreas, the brain and elsewhere in the body. The drug enhances these receptors, which help the pancreas make more insulin, in turn helping to reduce blood-sugar levels that can become elevated in people with diabetes.

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The drugs limit the amount of sugar that the liver releases into the bloodstream, and slow down how long food stays in the stomach. GLP-1 drugs contribute to weight loss by suppressing appetite and making you feel full sooner when you eat. Mounjaro also promotes a second gut hormone known as glucose-dependent insulinotropic polypeptide, or GIP, which is believed to enhance these effects to treat diabetes and obesity. Ozempic, Wegovy and Mounjaro are injected once weekly.

Ozempic and Mounjaro areapproved for people with Type 2 diabetes, but doctors have discretion to prescribe them off-label for obesity because clinical studies showed they induced weight loss. Doctors generally should reserve such off-label prescriptions for people who meet criteria for being overweight or obese, but in some cases patients who meet neither of those criteria are still getting their hands on Ozempic to lose weight. Lilly is seeking FDA approval to market Mounjaro specifically for weight loss, in addition to its approved use in diabetes. 

Wegovy is approved for weight management in people with a body-mass index of at least 30—the criteria for obesity—or at least 27 in people who also have a weight-related condition such as high blood pressure. A BMI of 30 is equivalent to a 5-foot, 9-inch person who weighs at least 203 pounds. In studies, Wegovy helped people lose up to about 17% of their body weight, while Mounjaro helped people lose up to about 22.5% of their weight,on average. The studies for Ozempic weren’t designed to assess weight-management outcomes.

The drugs are expensive, ranging from $935 for an Ozempic injection pen that lasts a month, to $1,349 per 28-day supply of Wegovy pens in the U.S. Many insurers cover Ozempic and Mounjaro for diabetes, but coverage is spotty for their use in weight loss. Commercial insurance and Medicaidcoverage for Wegovy have been expanding, according to its manufacturer, Novo Nordisk. The drugmakers provide savings coupons for some eligible patients. The federal Medicare health program for the elderly doesn’t cover weight-loss drugs, though legislation has been proposed to enable such coverage.

The most common side effects are gastrointestinal difficulties such as nausea, vomiting and constipation. These side effects might subside for many patients as they become accustomed to the drugs, but for some they have been severe enough to cause them to stop taking the medications. There is also a risk of pancreatitis, or inflammation of the pancreas, and patients are advised to stop the treatment if that happens. Patients who have had thyroid cancer, or have a family history of it, shouldn’t take the drugs because similar tumors developed in animals during testing of the drugs. 

Some users have observed the development of what they call "Ozempic face," or a gaunt appearance, but doctors say the medications don’t target the face, and that kind of change in appearance can happen as a result of rapid weight loss. Some users have reported having strange and vivid dreams after starting prescriptions. Novo Nordisk said it doesn’t have enough information to say the drugs are causing these dreams, and Lilly declined to comment.

Many people have regained substantial weight after they stopped using semaglutide or tirzepatide. Researchers are monitoring whether the drugs need to be taken indefinitely to keep weight off, and if that is safe.

The effectiveness of Ozempic and similar medications has underscored how difficult it can be for people to lose weight from diet and exercise alone. Doctors specializing in obesity treatment say these drugs have the potential to help more people lose more weight than older approaches, which in turn can help reduce obesity-related complications such as heart disease.   

This article might be periodically updated.