In an endnote to the study, the researchers pointed to several limitations with the research. One is that marijuana can be detected in the blood up to one week after use. And, therefore, the researchers said, "the prevalence of nonalcohol drugs reported in this study should be interpreted as an indicator of drug use, not necessarily a measurement of drug impairment.
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And that still does not alter the fact that highway fatalities are at record lows, even in states that have fully legalized. Prohibitionists said that wouldn't happen.