(NewsNation) — Authorities are warning people to be cautious when buying Ozempic and other prescription weight loss drugs online after counterfeit versions have landed people in the hospital.

Two people in Austria were hospitalized after using counterfeit Ozempic pens. Originally used to treat Type 2 diabetes, Ozempic has surged in popularity for its off-label use as a weight loss aid. As demand for the drug has increased, so have online ads claiming to sell Ozempic without a prescription.

The patients in Austria reported symptoms including seizures and hypoglycemia, a sign that they may have received insulin instead of Ozempic. While insulin is necessary for the body to digest food, too much can be dangerous.

A small number of people in the United Kingdom were also hospitalized after taking what they believed to be Ozempic. Regulatory agencies in both countries confirmed they were investigating the incidents.

Novo Nordisk, the drug’s manufacturer, also said it was working with authorities in Europe, the UK and the U.S. to track down counterfeit versions of the medication. The Food and Drug Administration has also warned U.S. consumers to be wary of ads promising easy-to-access Ozempic without a doctor’s prescription.

Those who make counterfeit drugs go to great lengths to mimic the drug’s injection pen, but there are signs to help spot a fake. Some signs of a counterfeit include non-working bar codes, an injector pen that is a different color than the original or that has a transparent safety window as opposed to the grey window in the original. Consumers should also check the box and labeling for typos or other errors that indicate a knock-off product.

Experts say the safest way to avoid fakes is to purchase drugs through a reputable pharmacy with a doctor’s prescription.