Driving Under the Influence of Marijuana

June 20, 2018| By Bill Baumann | Auto/Motor, Personal Umbrella | English

Region: North America

As more states legalize marijuana for medical and recreational use, there is a rising concern about the risk of people getting behind the wheel while high. Marijuana can slow reaction time, impair judgment and distance, and decrease coordination. After alcohol, marijuana is the drug most often found in drivers involved in automobile accidents accounting for 35.6% of the drugs tested, according to the Federal National Highway Traffic Safety Administration (NHTSA).

As of April 2018, medical use of marijuana is legal in 37 states and the District of Columbia.

Recreational marijuana is allowed in nine states and the District of Columbia. Medical marijuana refers to the use, possession and/or cultivation of marijuana for medical purposes. Patients can access the drug if they are terminally ill, or suffer from painful or long-term symptoms associated with certain qualifying conditions such as epilepsy, HIV/AIDs, glaucoma, multiple sclerosis, muscular dystrophy, seizure disorders, post-traumatic stress disorder and cancer.

Motorists who live in states that permit using medical marijuana with a valid doctor’s recommendation could still be charged with driving under the influence. If the officer and/or drug recognition expert has gathered enough evidence of marijuana impairment, an otherwise valid medical exemption may not be used as a defense. In this regard, medical marijuana is no different than any other prescription drugs with the potential for impairment.1

Unlike alcohol, the psychoactive component of marijuana (THC) is detectable in a person’s urine and bloodstream for up to four or five weeks after use, and there is no way to conclusively detect actual impairment at a traffic stop. Laws and interpretations vary about the definition of drug impairment. Testing practices can also vary, but there are no uniform laws to determine how often testing is used at traffic stops and the type of drugs screened. There is currently no valid roadside device that police can use to test for marijuana and other drugs. Many officers lack training to identify those under the influence of drug-impaired driving, and delays in roadside testing may allow the drug to metabolize so the results do not accurately measure the concentration of drugs in the driver’s system at the time of the traffic stop.

Every state has laws dealing with alcohol-impaired driving and drug-impaired driving. But unlike the laws for drunk driving, those that address drugged driving are nuanced, difficult to enforce or prosecute and vary substantially by state.2 There are no field tests comparable to alcohol screening using a breathalyzer. Some jurisdictions use Drug Recognition Experts, trained police officers who follow specific guidelines to determine drug impairment in motorists.3

As more states legalize medical and recreational marijuana, the lack of uniformity grows wider in the way the states approach drugged driving. There is no national standard for drugged driving. A driver testing positive for marijuana does not necessarily mean impairment given the fact that cannabinoids can remain in the body’s system for weeks. Scientists are working to create a chemical test to replace the behavioral indicators that police officers base their judgment on during a traffic stop. The development of a roadside test would determine the level of impairment and would enforce the prosecution of driving under the influence of marijuana.


  3. Drug Recognition Experts
  4.; “Map-of-US-state-cannabis-laws” by Lokal_Profil. Licensed under CC BY-SA 2.5 via Wikimedia Commons - Colors adjusted.




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