​What constitutes driving while high? The medical marijuana boom in Colorado has led to a debate in the Legislature of driving while under the influence of pot.

Lawmakers are looking at setting a DUI blood-content threshold for marijuana that would make Colorado one of only three states with such a law, reports Ivan Moreno at The Associated Press . According to sponsor Rep. Claire Levy (D-Boulder), it would be one of the most liberal.

Drivers who test positive for five nanograms or more of THC, a psychoactive ingredient in marijuana, would be considered too impaired to drive under the proposal if the substance is present in their blood at the time they’re pulled over, or within two hours.

Levy admitted that medical marijuana advocates fear the law would restrict legitimate patients from using cannabis.