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Rapid Marijuana Saliva Test Detects Immediate Use within Minutes

cannabis saliva detector
The EPOCH system includes a sample processing kit, sensor cartridge, and detection cradle to detect optical signals of THC. | H. Yu et al., Science Translational Medicine 2021

A new, rapid test can detect recent marijuana use in the saliva of users within five minutes, according to a new study. Unlike standard drug tests, the test can also distinguish immediate use (within 12 hours) from less recent use.

The new technique, which was tested with 43 users of marijuana (or cannabis) and 43 non-users, features sensors that detect the drug far faster than standard tests. The test's speed could prove useful in situations such as roadside safety and precautionary self-testing, the study authors say.

With further improvements, the test could one day help meet the need for a fast, accurate, and more time-specific cannabis test as the drug increasingly becomes legalized for both medicinal and recreational purposes.

The testing platform was designed and evaluated in a new study published in the October 20 issue of Science Translational Medicine.

Rapid Testing in the Age of Legalization

Cannabis is one of the most widely consumed psychoactive drugs, with an estimated 43 million users in the U.S. and 200 million users worldwide, according to the 2018 National Survey on Drug Use and Health and the 2021 United Nations World Drug Report .

Although cannabis has been largely prohibited for decades, restrictions on the drug have gradually loosened in recent years in several countries. Advocates have pointed to the drug's medicinal potential as a treatment for chronic pain, glaucoma, post-traumatic stress disorder, and other conditions.

Meanwhile, federal or state laws that legalize recreational use have appeared in countries such as the Netherlands, Canada, and the U.S. As of 2020, cannabis has been legalized in 18 U.S. states for recreational use and in 36 U.S. states for medicinal use.

Despite the rising tide of legalization, many employers still regularly test for cannabis. The drug can impair a person's decision-making and ability to concentrate in the short term, so being intoxicated can be dangerous for employees who drive, operate heavy machinery, or perform similar tasks.

However, current tests for cannabis suffer from drawbacks that make them ill-suited for rapid testing in the age of legalization. For example, the "gold-standard" tests work by detecting tetrahydrocannabinol (THC) — the main psychoactive component of cannabis — in blood or urine samples. But these tests are slow and can take several days to process.

THC also often lingers in the bloodstream for weeks in regular users and can still trigger positive test results long after the last use. Public safety officials and employers have difficulty telling whether a person who tested positive has used cannabis very recently (less than 12 hours ago) or sometime in the past few weeks.

"With marijuana becoming more accessible, it is important for public safety to have an objective way to tell whether a person is under its influence," said Hakho Lee, associate professor at Harvard Medical School and senior author of the new study. "Find[ing] a parallel in roadside alcohol testing, we started to brainstorm a new sensor for on-site THC detection."

Introducing EPOCH

Lee, Hojeong Yu, a postdoctoral researcher at Harvard Medical school and lead author of the new study, and colleagues designed and built a new rapid cannabis testing system they named EPOCH.

EPOCH uses an optical sensor to detect THC in saliva samples, where the compound's presence correlates more closely with immediate cannabis use than it does when detected in blood or urine.

The sensor also includes features that allow the test to measure the amount of THC instead of only giving positive or negative results. The whole system can yield results within five minutes and can be docked with commercially available smartphones.

To measure their system's accuracy, the research team performed a proof-of-concept test with 43 users of either inhaled cannabis or THC-infused jelly and 43 non-users. The scientists gathered and tested saliva samples from the users within 10 minutes of use.

The EPOCH system quickly detected THC in all of the users within five minutes, while the non-users didn't show any significant differences in THC levels. Results from non-users weren't affected by smoking cigarettes, drinking coffee, or other variables that might interfere with saliva test results.

Lee's team continued to track THC levels in the cannabis users after the first test. They discovered that high THC concentrations in the test samples rapidly decreased in the hours after cannabis smoking. After six hours THC levels dropped to below 1 nanogram/milliliter, the detection guideline cutoff recommended by the European Driving Under the Influence of Drug, Alcohol and Medicines project.

"Combined with EPOCH's speed and simplicity, the oral THC test has the potential to become a practical surveillance tool," the study authors say.

Lee and Yu emphasize that more research is needed before the test can be deployed. They say further studies are necessary to define how quickly the oral THC concentrations decrease over time and to establish baseline differences between frequent and occasional cannabis users.

The researchers eventually plan to expand their test to detect other types of drugs, such as oxycodone and other synthetic opioids. "Since our device is a platform technology, we could readily detect different targets by switching capture [molecules]," said Lee.

[Credit for associated image: Elsa Olofsson/ Flickr]