The Accuracy of Marijuana Impairment Testing: A Closer Look

As marijuana becomes legal in more and more states, there is growing concern about its impact on driving safety. As such, many law enforcement agencies have started using Marijuana impairment test to identify drivers who may be under the influence of marijuana. This article aims to provide a comprehensive understanding of the basics of these tests, including what they are, how they work, and their accuracy.

Marijuana Impairment Tests, or MITs, are a type of field sobriety test used by law enforcement to assess the level of marijuana impairment in drivers. There are several different types of MITs, but the most commonly used are the standardized field sobriety test (SFST) and the Drug Recognition Expert (DRE) evaluation. The former is similar to the alcohol sobriety test, while the latter involves a detailed evaluation by a specially trained law enforcement officer.

The SFST consists of three parts: the horizontal gaze nystagmus (HGN) test, the walk-and-turn test, and the one-leg-stand test. During the HGN test, the officer looks for involuntary jerking of the eye as the driver follows a moving object with their eyes. This is a sign of impairment and can be caused by marijuana use. In the walk-and-turn test, the driver is asked to take nine steps along a straight line, turn on one foot, and walk back. Finally, in the one-leg-stand test, the driver must stand on one foot for a certain period of time. All three tests are designed to assess the driver’s balance, coordination and ability to follow instructions – all of which can be impaired by marijuana use.

The DRE evaluation, on the other hand, is a much more extensive assessment that is performed by a specially trained law enforcement officer. The process involves a series of tests and evaluations, including vital signs, pulse, temperature, blood pressure, eye examination, balance and coordination, pupil size, muscle tone, and a behavioral evaluation. The results of the DRE evaluation are used to identify which drug category the driver may have used and the level of impairment.

MITs are not only used to identify drivers who may be impaired by marijuana; they are also used to assess the level of impairment and provide evidence in court. However, it’s important to note that the accuracy of MITs can be impacted by many factors beyond marijuana use. For example, certain medications and medical conditions can cause similar symptoms to marijuana impairment and many drivers find the tests difficult regardless of substance use.

Despite their limitations, MITs are considered the best available option to assess marijuana impairment in the field. They have been rigorously tested and validated by law enforcement agencies across the country. However, it’s still important for drivers to understand their rights and limitations when it comes to marijuana impairment tests. If pulled over under suspicion of marijuana impairment, drivers have the right to refuse to take an MIT. However, this may result in penalties such as license suspension or arrest.


Marijuana Impairment Tests are an important tool for law enforcement agencies in identifying drivers who may be under the influence of marijuana. While they have their limitations, they are still considered the best available option for assessing impairment in the field. Drivers should understand these tests, how they work, and their limitations in order to best protect themselves on the road. As with any substance, it’s important to never drive under the influence of marijuana and to always prioritize the safety of yourself and others on the road.

William Thomas

William Thomas