Although synthetic marijuana is illegal under federal law, the National Football League (NFL) has not added the drug to its list of banned substances, USA Today reports.

The league does not typically test players for synthetic marijuana, although it does test them for drugs such as heroin, cocaine and regular marijuana.

NFL players were first linked to synthetic marijuana two years ago, the article notes. Two NFL players have been linked to synthetic marijuana so far this year–Patriots defensive end Chandler Jones and Seattle Seahawks fullback Derrick Coleman, according to the newspaper.

“As long as people are willing to do stupid things to their bodies, we are going to have problems with these kinds of drugs,” DEA spokesman Rusty Payne told the newspaper. “This is not something you can legislate or arrest your way out of to solve.”

NFL spokesman Brian McCarthy said, “Synthetic marijuana is not currently part of the basic testing panel, but the medical advisors have the discretion to add it to an individual’s testing panel as appropriate.” According to a joint drug agreement between the NFL and NFL Players Association, that discretion occurs after a player is already in the league’s drug program because of an earlier violation.

In November 2015, the American Association of Poison Control Centers (AAPCC) said that calls to poison control centers regarding synthetic marijuana had almost doubled since last year. The drug, which is made of various chemicals sprayed on plant material, is sending thousands of people to emergency rooms. The drug is also known as synthetic cannibinoids, “K2” or “Spice.”

Synthetic cannibinoids are very different from marijuana, the AAPCC explained. They can cause dangerous health effects, including severe agitation and anxiety; muscle spasms, seizures and tremors; intense hallucinations and psychotic episodes; and suicidal and other harmful thoughts and/or actions.