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How Do Police Test for Marijuana?

By March 15, 2021October 21st, 2021One Comment

It shouldn’t be a surprise that there are harsh legal penalties for driving under the influence of alcohol. What many people don’t realize, though, is that you can also receive a driving under the influence (DUI) charge for marijuana.

In states where marijuana is legal, assessing the driver’s degree of mental impairment is critical to deciding whether or not to arrest an individual who is suspected of driving under the influence.

Roadside tests designed to determine whether you’re driving under the influence of marijuana will vary state to state, so it’s worth reading up on the regulations in your state so you are aware of how officers may assess suspected drivers. In California, for example, officers conduct field sobriety tests, which are a series of physical and mental exercises that determine a driver’s level of impairment. These exercises may include the following:

  • The “horizontal gaze nystagmus test” involves an officer moving their finger from side to side while you follow their finger with your gaze. When you’re high, these eye movements may provoke an involuntary jerking, or quivering, of your eyes, which may signal that you’re under the influence.
  • The “walk and turn test” involves you walking in a straight line in a heel-to-toe fashion. Any loss of balance, inability to stay on the line, breaks in walking, or beginning before instructed, raises some flags, because these mistakes hint at a potential lack of motor coordination and lack of inhibition secondary to substance use.
  • The “one leg stand test” involves an officer instructing you to raise your foot, hold still, count, and then look down. Things like swaying, hopping, or putting your foot down prematurely raises the suspicion for marijuana intoxication. This is because the test is designed to split your attention between the various tasks, which can be demonstrably more difficult while under the influence of marijuana.

Officers may also assess for physical signs of marijuana intoxication, including dilated pupils, rapid breathing, rapid heart rate, red eyes, or an apparent odor of marijuana.

Other forms of detection for marijuana use include blood, breath, urine, or saliva tests; these tend to be less common in the context of DUI assessments because they take longer to perform. They may, however, be administered if the officer has probable cause to believe you are driving under the influence of marijuana or another substance. There is no consensus on how much marijuana can be detected on these tests to indicate whether you are impaired while driving, and precise guidelines will vary by state.

About is a free, web-based resource and community created by a team of healthcare professionals and researchers. We distill the facts about marijuana use and its effects into practical guidance for interested persons or for those who are thinking about or struggling to quit weed. Finding reliable, easy to understand information about marijuana should never be a struggle—that is why our core mission is to provide the most up to date information about marijuana use, abuse, addiction, and withdrawal. While we seek to empower individuals to have control over their use, we are not “anti-weed” and we support efforts to legalize adult marijuana use and study.

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