KOKOMO, Ind. (AP) — An Indiana doctor is warning patients to be careful when purchasing cannabidiol following the recent state law that authorized the widespread sale of the cannabis-derived oil.

The Kokomo Tribune reports that Dr. Gary Gettelfinger, who practices out of IU Health Pain Center in Bloomington, has provided the supplement to more than 500 patients since it first became legal in Indiana to treat children with epilepsy.

Gettelfinger says some versions of cannabidiol, commonly referred to as CBD, can be toxic and cause a user to fail a drug test. He recommends that users buy organic, check the product’s absorption and check the levels of THC, which is the psychoactive compound found in cannabis plants.

CBD is believed to have therapeutic benefits and help with anxiety, insomnia, depression and epileptic seizures.