The U.S. Food and Drug Administration is warning consumers not to use off-brand versions of the popular weight-loss drugs Ozempic and Wegovy because they might not contain the same ingredients as the prescription products and may not be safe or effective.

Agency officials said this week that they have received reports of problems after patients used versions of semaglutide, the active ingredient in the brand-name medications, which have been compounded, or mixed in pharmacies. Officials didn’t say what the problems were.

The trouble is that those versions, often sold online, contain a version of semaglutide that is used in lab research and has not been approved for use in people.

“Compounded drugs are not FDA-approved, and the agency does not verify the safety or effectiveness of compounded drugs,” the notice said.

Sales of semaglutide products have soared in the past few years after the drug was shown to spur fast and significant weight loss. The drugs manufactured by Novo Nordisk include brands Ozempic and Rybelsus, used to treat diabetes, and Wegovy, approved to treat obesity.

Demand for the medications has outstripped supply. As of May, Ozempic and Wegovy remain on the FDA’s list of drug shortages. When drugs are in short supply, compounding pharmacies are permitted to produce versions of those medications.

Consumers should only use drugs containing semaglutide with a prescription from a licensed health care provider and obtained from a state-licensed pharmacy or other facilities registered with the FDA, the agency said.