A team of analysts has developed a urine screening method that is sensitive enough to detect even small amounts of the chemicals that result from exposure to cannabis.

The team in the United States says that its work should be viewed against a background of increased legalisation of marijuana for medicinal and recreational purposes in the US and growing concern about the potential health effects of its second-hand smoke. Writing in the American Chemical Society’s journal Analytical Chemistry, the team say that current drug tests can detect large amounts of the psychoactive marijuana component tetrahydrocannabinol (THC) and its metabolites in urine.

That, they say, is sufficient when testing whether or not a potential employee or professional athlete has used the drug but in the case of second-hand marijuana smoke, the levels of the substances in the urine are too low to be recorded, making it difficult to assess if this type of exposure could cause harmful health effects. As a first step toward investigating the effect of second-hand marijuana smoke exposure, Binnian Wei and colleagues at the U.S. Centers for Disease Control and Prevention sought to develop a more sensitive urine test for cannabinoids.

The researchers combined ultrahigh performance liquid chromatography and tandem mass spectrometry with positive electrospray ionization to develop a reliable, fast and accurate method to test for THC and its metabolites. The approach is 10 to 100 times more sensitive than current methods. In laboratory tests, the method detected the substances at levels approximating those that would be in the urine of someone exposed to second-hand marijuana smoke. The team were supported by funding from the Centers for Disease Control and Prevention and the work comes as reports suggest that marijuana use in the US has more than doubled since 2001, with women, middle aged and older people, Hispanic and black people showing notable increases. Researchers, who say the number of adults that had used marijuana in the past year rose from 4.1% in 2001 to 9.5% in 2013, based their findings on data from the National Epidemiologic Survey on Alcohol and Related Conditions. The researchers, writing in the journal JAMA Psychiatry, looked at rates of marijuana use and marijuana use disorders. They found that prevalence of marijuana use had increased among people aged between 45 and 64, black and Hispanic people, women, those living in the South, and those with the lowest incomes.

The study comes as 23 states have legalised medical marijuana, with four of these allowing the drug for recreational purposes. Authors said that along with the increase in use, they also saw a rise in marijuana use disorders – which they say should serve as a caution regarding the relaxation of laws surrounding the drug. They reported that rates of marijuana use disorder, which includes abuse or dependence, rose from 1.5% in 2001/2002 to 2.9% in 2012/13, accounting for 6.8 million people in the US, or three in every ten marijuana users.