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How dangerous is driving under the influence of marijuana?

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The question of driving stoned was taken up by a committee in the House of Representatives this week, a response to the changing landscape in marijuana law across the country.

More than 20 states have legalized the drug in some form and last weekend the New York Times editorial board endorsed an end to pot prohibition. So how will all this affect the safety of the road?

Dr. Marilyn Huestis, a senior investigator at the National Institute on Drug Abuse said current research shows drivers using cannabis are at twice the risk of getting into an accident or a fatal accident.

That's less than for alcohol, which gives an individual an eight or nine times greater risk, but it is a strong correlation.

"The higher the concentration of THC, the primary psychoactive compound in cannabis, just like the higher the amount of ethanol you have for an alcohol test, the greater the odds," said Huestis.

Depending on the frequency with which the user takes cannabis, the effects can be milder or more pronounced, according to Huestis. Habitual users of marijuana will become more tolerant and less affected than others who use the drug infrequently. But it will still affect things like decision-making and peripheral vision.