Updated on August 16, 2020.
Medical content reviewed by Dr. Joseph Rosado, MD, M.B.A, Chief Medical Officer
The percentage of fatal crashes involving drivers who tested
positive for THC in Washington State more than doubled since before marijuana
became legalized there, according to a new study by AAA’s Foundation for
An estimated 21% of all drivers involved in fatal crashes in
the state in 2017 tested positive for THC, the psychoactive component in marijuana.
confirmed an earlier study conducted only two years after the law
The actual number of drivers involved in a fatal crash in Washington
who tested positive for THC more than tripled from five years before the law
took effect to five years after, although this also reflects an increase in the
total number of fatal crashes.
The authors emphasized that this study did not examine fault for the crashes, meaning the THC-positive drivers did not necessarily cause the crashes. Having detectable THC in blood does not prove that a person has recently used cannabis and is impaired. THC can stay in the blood for many hours and even days after the impairment wears off, especially in frequent marijuana users. Impairment typically wears off within about 2 to 3.5 hours of smoking, according to the study.
However, other studies have linked cannabis use to an increase in crashes, with one showing that the legalization of recreational marijuana in Washington, Colorado, and Oregon was associated with increased collision claim frequencies compared to states without these laws.