Lawmakers and law enforcement officials are struggling to find a clear way to determine if a driver is too drugged to drive. There are many factors that lead to this difficulty:

• differences in the way drugs are metabolized compared to alcohol
• the vast number of drugs that can be consumed, both legally and illegally
• the lack of reliable, inexpensive, roadside tests that could be compared to a Breathalyzer.

THC, the psychoactive compound in marijuana, is fat soluble. Rather than moving into the blood like alcohol does, it gets soaked up by body fat. Studies have previously shown that you can measure THC in the brain (a fatty tissue) even if you can no longer detect it in someone’s blood.

Dr. Marilyn Huestis, a researcher at the National Institute on Drug Abuse (NIDA), found that for occasional users, THC has rapidly cleared out of the blood within a few hours of smoking. This means you could still be impaired but not registering much THC in your blood. For chronic, frequent smokers, (near daily for 3 months or longer) Huestis told NPR:

We found [their] brains had changed and reduced the density of cannabinoid receptors.

Driving stoned is a serious issue, which is beginning to see more attention.

These users showed cognitive impairment for up to 28 days after their last use. Although they may not have much THC detectable in their blood, they could still be considered too impaired to drive safely during that time. Driving stoned can be just as dangerous as driving drunk, particularly for those who are extremely high. Casual users may have a lower blood THC content than corresponds to their impairment. Long term users may have blood THC levels that show impairment (and may have cognitive impairment) for weeks after they have stopped using.

While fewer drivers are getting behind the wheel after drinking, incidents of driving stoned or high have been increasing. Make sure your family has a plan for what to do if a driver begins drinking or using. Ohio is working on a campaign to discourage drugged driving.