Scientists develop rapid tests for marijuana use
Detection in saliva in less than 5 minutes
Justin Wong (JW)October 5, 2026
Researchers may be one step closer to developing the equivalent of an alcohol test for detecting marijuana use.
In a first study, the scientists found that their rapid test is able to reliably detect THC in people's saliva in less than 5 minutes. THC, short for tetrahydrocannabinol, is the active ingredient in marijuana.
Currently, the "gold standard" for detecting marijuana use is by measuring THC in blood or urine. However, these tests can take days to complete. Another disadvantage is that, unlike alcohol, THC can linger in the blood for days or even weeks - so a "positive" blood test does not necessarily reflect recent consumption.
These facts have made it difficult to develop a street test for marijuana use, similar to the breath test used to measure alcohol levels by drivers.
However, THC in saliva reflects marijuana use over the past 12 hours, said Hakho Lee, the lead researcher on the new study.
Some saliva tests for THC already exist, but they are hampered by issues like slow processing times or "binary" results - much like a yes / no on a pregnancy test.
Lee said his team was able to develop a test that not only quickly detects THC in saliva, but also quantifies the amount.
In initial tests with 43 marijuana users and 43 non-users, THC was accurately detected in the saliva samples of all drug users.
According to Lee, who works at the Systems Biology Center at Massachusetts General Hospital in Boston, it took about 3 minutes to get the result.
The researchers also used the test to watch how THC levels in marijuana users changed over time. Overall, the THC levels in saliva decreased relatively quickly after smoking the drug - although the levels were still above 1 ng / ml six hours later. This is the limit recommended by the European project "Driving Under the Influence of Drugs, Alcohol and Medicines".
Another problem is that - unlike alcohol - there is no THC content that defines a "high". It's complicated, Lee explains, because the level of impairment associated with a given concentration of THC varies - depending on, for example, how the marijuana is consumed and whether the person is a regular user.
However, with further refinements, his team's quick test could prove useful for roadside testing of drivers who are suspected of being impaired. And there are even potential uses for the public, he noted. One of them is checking breast milk so babies don't accidentally come into contact with THC.
The initial results of the test are "very encouraging," said Dr. Guohua Li, professor at Columbia University Mailman School of Public Health in New York City.
Li, who was not involved in the research, studies the role of drugs in traffic accidents and other injuries.
"The evidence is overwhelming and consistently shows a link between [marijuana] use and an increased risk of being involved in a fatal accident," said Li.
The risk associated with marijuana use alone isn't as great as that of drunk driving, Li said. But, on average, Li said, drivers who have used marijuana are about twice as likely to be being involved in a fatal accident, like non-consumers.
Added to this, Li said, is the increasing prevalence of marijuana use. In the past few decades, the proportion of fatally injured drivers in whom THC was detected in the blood has increased significantly.
The latest results, Li said, are "proof of the concept" that a rapid road test for THC is possible. But a lot more work is needed before it can be used in practice, "he added.
The results were published in the journal Science Translational Medicine on October 20. Lee and several fellow researchers are listed as inventors on a patent application covering the test.
