The Food and Drug Administration has issued warnings to more than 350 medical practices that might have received counterfeit versions of Irvine-based Allergan Inc.’s flagship Botox.

Botox is marketed as a treatment for wrinkles and other uses, including some cases of migraine headaches.

The FDA said the shipments from some Canada-based suppliers were unapproved and might be counterfeit or unsafe. The warning came in a letter that went to the medical practices in November and was recently made public.

The agency tied the concerns to shipments from various suppliers controlled by Canada Drugs, an Internet pharmacy based in Winnipeg. The company was tied earlier this to charges that it sold fake cancer drugs to doctors through its distribution network.

Regulators cautioned doctors against purchasing drugs from sellers other than licensed U.S. pharmacies.

Allergan added its own caution on Botox.

“(W)e cannot confirm the safety or authenticity of products that are imported from unauthorized distributors,” a spokesperson for the company told the Wall Street Journal

Allergan’s shares were about even at $92 for a market value of $27.7 billion in trading today.