At the most advanced driving simulator in the world, at the University of Iowa, a study on the effects of driving under the influence of cannabis has been in high gear. Dr. Marilyn Huestis has been studying cannabis for 20 years and showed "" around the lab two years ago.
"The ability to take information in, evaluate it, make decisions and initiate them, greatly affected by cannabis," she said.
Those potential dangers are at the heart of a study from the University of Michigan published on Wednesday. Of the nearly 800 of Michigan medical cannabis users surveyed, 51 percent admitted to driving while "a little high" and 21 percent said they had driven while "very high."
That's a concern for law enforcement. There are 2.1 million medical marijuana users across 33 states. Right now, there is no reliable roadside test to know for sure if a driver is impaired by cannabis.
Neurologist Dr. Orrin Devinsky of NYU Langone Health conducted the trials that led to the first FDA approved cannabis medication, a drug for epilepsy. He believes the use of medical marijuana and the legislation of it has gotten ahead of the science.
"Essentially politicians have voted that this should be a legal medical therapy and we don't have data from rigorous scientific studies to define what the safety is," he said.
It's significant that Devinsky, a pioneer in medical cannabis use, is concerned. He said we need more specific guidance on how to use it in as safe a way as possible. That includes being able to tell patients how long to wait before driving and figuring out ways to reliably know what role it may be playing in motor vehicle accidents.