CNN reports in an article titled Weed impairs driving skills long after the high is gone that heavy users of recreational cannabis are poor drivers.

Speeding, running red lights, crossing into oncoming lanes, and even hitting pedestrians. These are some of the dangerous driving behaviours that a new study in the journal Drug and Alcohol Dependence found – even in drivers that weren’t high.

“Heavy use was defined by daily or near daily use, a minimum of four or five times a week, with a lifetime exposure of 1,500 times”, the article quotes the director of the Marijuana Investigations for Neuroscientific Discovery (MIND), Staci Gruber.

MIND is a program at McLean Hospital, the largest psychiatric teaching hospital of Harvard Medical School.

Participants of the study had not used cannabis for at least 12 hours. Based on urine drug screening they were not intoxicated by THC, the main active compound in cannabis.

The worst drivers were those who began using regularly before age 16.