The U.S. Food and Drug Administration is warning that people are overdosing on compounded semaglutide injectable products, which include the weight-loss drugs Wegovy and Ozempic, among others.

FDA-approved versions of the drugs come in pre-filled injection pens or oral tablets, but compounded semaglutide products are widely available on the market.

The agency says compounded drugs pose higher risks than the FDA-approved versions, and should only be used for patients “whose medical needs cannot be met by an available FDA-approved drug.”

The FDA said patients are self-injecting incorrect doses due to confusion on the parts of both patients and health care providers. In some cases, patients are incorrectly measuring doses of the injectable drugs from vials, or misunderstanding how multi-dose vials work.

In other cases, health care providers themselves are miscalculating doses of the drug.

Patients’ “unfamiliarity with withdrawing medication from a vial into a syringe and coupled with confusion between different units of measurement (e.g., milliliters, milligrams and “units”) may have contributed to dosing errors,” the agency said.

The FDA also said health care providers should “be vigilant” about the different available concentrations of compounded semaglutide, and if uncertain, should contact the compounder about calculating the correct dose of medication to prescribe or administer.

The majority of adverse events reported involve patients drawing up more than the prescribed dose from a multiple-dose vial. Those patients self-administered five to 20 times more than the intended dosage.

In some cases, patients were advised to use U-100 1-milliliter insulin syringes to draw small 5-unit, or 0.05 milliliter, doses. But the patients mistakenly drew 50 units instead.

In one case, a patient reported receiving unclear instructions from a health care provider and turning to the internet instead.

“In one reported case, it was difficult for the patient to obtain clarity on dosing instructions from the telemedicine provider, who prescribed the compounded semaglutide, leading the patient to conduct an online search for medical advice and resulting in the patient taking five times the intended dose,” the FDA wrote.

Providers have also made dosing errors. In one case, a provider intended to dose five units but prescribed 25 units. Another prescribed 20 units instead of two units. Another health care provider who was also using the drug inadvertently self-administered 10 times the intended dosage.

Adverse effects of overdosing on semaglutide include severe nausea, severe vomiting and severe hypoglycemia (low blood sugar levels).