Friday, November 18, 2016

Why is it so hard to make a sobriety test for marijuana? | Igor Grant | Opinion | The Guardian

Why is it so hard to make a sobriety test for marijuana? | Igor Grant | Opinion | The Guardian

Unlike alcohol, the amount of pot in someone’s blood doesn’t necessarily correlate with the ability to drive safely. We must learn how to assess the risk

On 8 November, voters in CaliforniaMaineMassachusetts and Nevadaapproved ballot measures to legalize recreational cannabis. It is now legal in a total of eight states. This creates potential problems for road safety. How do we determine who’s impaired and who’s not?
The effects of alcohol vary based on a person’s size and weight, metabolic rate, related food intake and the type and amount of beverage consumed. Even so, alcohol consumption produces fairly straightforward results: the more you drink, the worse you drive. Factors like body size and drinking experience can shift the correlation slightly, but the relationship is still pretty linear, enough to be able to confidently develop a blood alcohol content scale for legally determining drunk driving. Not so with marijuana....
But how do you know when you’re too stoned to drive? How can police tell?
My colleagues and I at the Center for Medicinal Cannabis Research at UC San Diego have received a $1.8m grant from the state of California to gather data about dosages, time and what it takes to impair driving ability – and then create a viable roadside sobriety test for cannabis.
Alcohol and marijuana both affect mental function, which means they can both impair driving ability.
Some elements of cannabis use are similar. Potency of strain affects potency of effect. Marijuana and its active ingredient – THC – alter brain function, affecting processes like attention, perception and coordination, which are necessary for a complex behavior like driving a car.
Regular users tend to become accustomed to the drug, particularly in terms of cognitive disruption or psycho-motor skills. Because they are accustomed to the drug’s effects, this means they may function better relative to naive users....

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