Recreational marijuana is slowly but steadily being legalized in the US. However, there are not enough laws governing its use, unlike alcohol. A new device is expected to change that as it could help in applying driving under influence (DUI) laws to marijuana smokers.

Researchers from the Department of Chemistry, University of Pittsburgh and the Swanson School of Engineering, have developed a breathalyser that will measure the amount of Tetrahydrocannabinol (THC) in a person's breath. THC is the psychoactive compound in marijuana.

The breathalyser will provide mobility to a drug test. Currently, these tests are done using blood, urine and hair samples which cannot be done in the field unlike DUI tests for alcohol. These old tests are only capable of determining that the user has only recently inhaled the drug, but not that they are under the influence.

The breathalyser is made using carbon nanotubes tinier than a human hair. When a person breathes into the breathalyser, THC particles in his/her breath get attracted to the surface of the nanotubes and change their electrical properties. The speed of recovery of these electrical tubes will determine whether THC is present in a person's breath or not.

"The semiconductor carbon nanotubes that we are using weren't available even a few years ago. We used machine learning to 'teach' the breathalyser to recognize the presence of THC based on the electrical currents' recovery time, even when there are other substances, like alcohol, present in the breath," Sean Hwang, lead author on the paper and a doctoral candidate in chemistry at the University of Pittsburgh told

The marijuana breathalyser will look similar to the one used for alcohol with plastic casing, a mouthpiece, and digital display.

The researchers say that the prototype is in the testing phase and will soon be available for manufacturing.

"In legal states, you'll see road signs that say 'Drive High, Get a DUI,' but there has not been a reliable and practical way to enforce that. There are debates in the legal community about what levels of THC would amount to a DUI, but creating such a device is an important first step toward making sure people don't partake and drive," Dr. Alexander Star, a professor of chemistry who worked with Hwang, said on the matter.

While marijuana DUI laws are yet to go through the Congress, it poses certain legal challenges, the same as the ones that came up during marijuana legalization. The most prominent one will be whether it will be treated at the same level as alcohol despite its differentiating features such as lack of overdose.

Elon Musk some joint
Elon Musk smokes joint on comedian Joe Rogan's web show. Screengrab