Study looks at driving under influence of pot

IOWA CITY — Marijuana use, despite the legal implications, has been common in America for generations, and it's becoming even more widespread as some communities legalize it for medical purposes.

But it wasn't until five years ago that the National Highway Traffic Safety Administration looked into its prevalence behind the wheel and found that 16.3 percent of the weekend nighttime drivers surveyed at 300 locations across the United States were drug positive.

Cannabis stood out as the most commonly detected drug, according to the survey. But what the survey didn't show — and what authorities don't know — is how often drivers are impaired by the drugs, specifically marijuana.

Some states prohibit drugged driving all together while others require proof of impairment, but few studies have actually analyzed the effects of cannabis behind the wheel — until now.

The National Highway Traffic Safety Administration is teaming up with the National Institute on Drug Abuse to conduct the first study to analyze the effects of inhaled cannabis on driving performance. The study is taking place at the University of Iowa's National Advanced Driving Simulator, praised as being the most advanced simulator in the world, and pilot work is scheduled to begin later this month.

Marilyn Huestis, chief of chemistry and drug metabolism at the intramural research program for the National Institute on Drug Abuse, has been trying to get the UI simulator involved in drugged driving studies for years. New, top-quality research could help shape future legislation in the United States, which Huestis said is behind in its policies on drugged driving.

``It's so important for it to be done there,'' she said. ``But it's taken a lot to get the United States to recognize the problem.''

The study will use about 20 volunteers, ages 21 to 55, who live within 40 miles of the UI and are able to make eight study visits — six of which will involve overnight stays at the University of Iowa Hospitals and Clinics. Participants must be in good health, have good sleep habits and be alcohol and marijuana consumers.

They must be willing to go through drug and pregnancy screenings, including blood draws.

Huestis said the study had to be approved by boards associated with the UI, the Federal Drug Administration and other local and national drug enforcement agencies.

``The regulatory reviews are extensive and meant to develop a study with high merit,'' she said.

Cannabis used in the study will come from a federally funded laboratory at the University of Mississippi, the nation's only facility allowed to grow marijuana for medical and research purposes. It involves a ``tightly controlled process'' involving the FDA and the U.S. Drug Enforcement Administration, according to Huestis.

``It is all very legal,'' she said. ``We have all the approvals in place, and we are starting the pilot data — but it's very costly and difficult to perform.''

Volunteers for the UI study will be transported to and from the study — they will not be allowed to drive while participating — and they will be ``dosed'' under the supervision of medical professionals, driving simulator officials said.

Volunteers will get paid to participate in the study, although compensation amounts are kept private.

And, even though participants will be asked to disclose details of their marijuana use, the UI uses a ``certificate of confidentiality'' from the U.S. Department of Health and Human Services that protects information about participants. The certificate, according to UI officials, verifies that no information about participants will be disclosed to anyone, including law enforcement.

Although few studies have been done on how marijuana affects a person's ability to drive, decades of research has shown its effects on the brain.

``It is very much involved in movement and control,'' Huestis said, ``in memory and decision making.''

Driving requires a lot of divided attention, with the need to stay in a lane, track turns in the road, monitor other drivers and handle unexpected events that might require a person to slam on the breaks or swerve, according to Huestis. Cannabis affects a person's ability to divide his or her attention, which is why, in crafting the drive for the study, Huestis included a number of unexpected occurrences. She also crafted a portion of the trip at the other extreme.

``There are long periods of monotonous driving, because it turns out a person's ability for sustained attention also is dramatically affected by cannabis,'' she said.

Tim Brown, associate research scientist with the UI's advanced driving simulator, said plenty of research has been done on the effects of drinking alcohol and driving, and with the prevalence of marijuana use today — especially considering the 2007 roadside survey findings — similar impairment data is needed for the drug.

``We don't know what the impacts are,'' he said. ``And that creates challenges when someone has a medical marijuana card.''

Medical marijuana is legal now in 17 states and Washington D.C., although it is illegal in all states to drive under the influence of any drug, regardless of whether it was prescribed by a physician, if the drug is causing impairment.

Impairment can be difficult to prove, but 17 states — including Iowa — have passed ``drug per se'' laws that simply make it illegal to operate a vehicle with certain drugs in one's system. Most of those states, like Iowa, do not tolerate any amount of the prohibited drugs in a driver's system.

Huestis said the list of states with drug per se laws is growing, and there is a push for a federal pro se law that would create a blanket prohibition against driving with one of the prohibited drugs on board.

Education, through studies like the one about to take place at Iowa, is expected to further the discussion about legislation and enable more-informed enforcement, Huestis said. It could even aid in the creation of an equivalent to the 0.08 blood alcohol content level set for driving.

``From an education and prevention point of view, this is very important,'' she said.