QUOTE

For marijuana, and for a number of other legal and illegal drugs including antidepressants, painkillers, stimulants and the like, there is no statistically significant change in the risk of a crash associated with using that drug prior to driving.
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Several states have passed laws attempting to define "marijuana-impaired driving" similarly to drunk driving. Colorado, for instance, sets a blood THC threshold of 0.5 nanograms per millilitre. But that number tells us next to nothing about whether a person is impaired or fit to drive. The implication is that these states are locking up people who are perfectly sober.