In a study of six adults, Johns Hopkins Medicine researchers report evidence that a single vaping episode of cannabis that is similar in chemical composition to that found in legal hemp products could possibly result in positive results on urine drug screening tests commonly used by many employers and criminal justice or school systems.

The U.S. government defines hemp as any crop of cannabis containing 0.3% THC or less in dry weight. THC (delta-9-tetrahydrocannabinol) is the substance in cannabis that confers a “high” and produces the subjective and cognitive effects that are typically synonymous with cannabis. The 2018 U.S. Farm Bill legalized the production and sale of hemp, and now as a result, consumer hemp products, such as oils, vaping cartridges and hemp flowers for smoking can be legally purchased in specialty stores, general retail stores and through websites across the U.S.

Hemp is now increasingly finding use in medicine and wellness markets, particularly for its component CBD, short for cannabidiol, which is one of the more than 100 cannabinoids found in the cannabis plant. According to New York-based investment bank Cowen & Co., the market for CBD last year ranged from $600 million and $2 billion in sales. Despite the size of this booming industry, it remains largely unregulated.

In a paper published Nov. 4 in the Journal of Analytical Toxicology, the researchers report that two out of six study participants tested positive after vaping cannabis that contained 0.39% THC using urine testing methods that are consistent with testing frequently performed for employment-related or criminal justice-related urine drug testing programs. Though the cannabis used in this study does not currently meet the federal definition of hemp, the THC concentration of 0.39% exceeds federal regulation by just 0.09%.

“People who use legal hemp products for medical intent rarely just use them once as we did in this study, and prior studies show that THC and its metabolites may accumulate with repeated use,” says postdoctoral fellow Tory Spindle, Ph.D., a researcher in the Behavioral Pharmacology Research Unit at the Johns Hopkins Bayview Medical Center. “What this means is that people need to be wary of single-dose or cumulative THC exposure and be aware that these now legal products may cause an unexpected positive result on a drug test.”

“Because the market for CBD products is so new and the popularity of use is growing so quickly, we want the public to be aware that a positive drug test is possible,” says Ryan Vandrey, Ph.D., associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine. Vandrey and his collaborators at the University of Pennsylvania previously showed in a