There are more than 80 active chemicals in marijuana. Today, in an “important medical advance,” the FDA approved the first prescription drug made from marijuana, still illegal by federal government standards, based on one of those chemicals.

“This product approval demonstrates that advancing sound scientific research to investigate ingredients derived from marijuana can lead to important therapies,” FDA Commissioner Scott Gottlieb says.

The approved medication, named Epidiolex, is targeted to treat two rare, severe forms of epilepsy in patients 2 years and older, says Gottlieb. The medication is a purified form of a chemical ingredient found in the cannabis plant known as cannabidiol, or CBD. It reduces seizures in some people with epilepsy.

CBD is one of more than 80 chemicals found in marijuana. It doesn’t contain THC, the key psychoactive ingredient in  marijuana. The approval is for a purified form of CBD.

The decision showed a “milestone that  could spur more research” into marijuana, according to Associated Press.

“This is an important medical advance. But it’s also important to note that this is not an approval of marijuana or all of its components,” the FDA chief says.