Scientists develop quick test for marijuana use

A new test developed by scientists can tell if someone has recently used marijuana in as little as one minute. The findings could help employers detect drug use and reduce the risk of accidents on the job.



Researchers may be one step closer to building a marijuana-detection device similar to a Breathalyzer.

Scientists discovered that their quick test could successfully identify THC in people’s saliva in just 5 minutes in an early investigation. The active element in marijuana is tetrahydrocannabinol (THC).

THC levels in the blood or urine are now the “gold standard” for identifying marijuana usage. However, processing such tests might take days. Another disadvantage is that, unlike alcohol, THC may stay in the system for days or even weeks, meaning that a “positive” blood test does not always indicate recent usage.

Because of these factors, developing a roadside test for marijuana usage, similar to the Breathalyzer used to monitor drivers’ alcohol levels, has been difficult.

THC in saliva, on the other hand, indicates marijuana usage during the previous 12 hours, according to Hakho Lee, the study’s main researcher.

Existing saliva tests for THC are limited by factors such as lengthy processing time or “binary” findings, which are analogous to a yes/no on a pregnancy test.

Lee claims that his team was able to create a test that not only detects but also measures THC in saliva.

It correctly detected THC in saliva samples from all marijuana users in early testing with 43 marijuana users and 43 non-users.

According to Lee, who works at Massachusetts General Hospital’s Center for Systems Biology in Boston, it took roughly 3 minutes from “sample in” to “result out.”

The test was also used by the researchers to track how THC levels in marijuana users varied over time. THC levels in saliva decreased quite fast after subjects smoked the substance, however they remained over 1 ng/ml 6 hours later. The European Driving Under the Influence of Drugs, Alcohol, and Medicines initiative recommends this limit.

A larger difficulty is that, unlike alcohol, there is no one THC concentration that constitutes “intoxication.” This is tricky, according to Lee, since the amount of impairment associated with a specific THC content changes depending on how the marijuana is eaten and whether the individual is a habitual user, among other factors.

Even so, Lee believes his team’s quick test might be beneficial for roadside testing of drivers suspected of being inebriated with additional development. He also said that there may be public applications. One is to examine breast milk for THC to ensure that newborns are not exposed to it accidently.

The test’s early results are “extremely promising,” according to Dr. Guohua Li of Columbia University’s Mailman School of Public Health in New York City.

Li, who was not engaged in the study, is a researcher who looks at the effect of drugs in traffic accidents and other types of injuries.

“The data is substantial and consistent,” Li added, “indicating a link between [marijuana] usage and a higher probability of being involved in a fatal collision.”

According to Li, the danger of marijuana usage alone is not as high as the risk of driving when inebriated. However, drivers who have used marijuana have nearly double the chance of being involved in a fatal collision as non-users, according to him.

There’s also the increased prevalence of marijuana usage, as Li pointed out. According to him, the percentage of fatally wounded drivers with THC in their systems has increased dramatically over the last two decades.

The current results, according to Li, provide “proof of concept” for a quick THC test on the road. But, he noted, “far more work is required before it can be utilized in the field.”

The results were reported in Science Translational Medicine on Wednesday. On a patent application for the test, Lee and other co-researchers are mentioned as inventors.

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