Hemp is a crop grown for durable fiber and nutritious seed while marijuana is the most abundant illegal drug of abuse in the United States. However, both plants belong to the species cannabis sativa and even if they differ in levels of the psychoactive drug tetrahydrocannabinol (THC) are difficult to tell apart.

Two researchers from the University of Minnesota are the first to successfully separate hemp plants from marijuana plants with genetic markers. The report of the study appears in the March issue (volume 51, No. 2) of the Journal of Forensic Science.

The new technique is an improvement on previous means of separating the two types of Cannabis, said author George Weiblen, an assistant professor of plant biology in the university's College of Biological Sciences and College of Food, Agricultural and Natural Resource Sciences. For decades it has been possible to identify THC chemically, but the drug is not present in all plant tissues or throughout a plant's life cycle. And other researchers have found that genetic markers known as "short tandem repeats," which are used to identify individuals in paternity and criminal cases, lack the power to distinguish Cannabis cultivars unequivocally.

The researchers believe that the technique also has the potential to distinguish marijuana varieties. The implications are not just for separating hemp from marijuana in countries where hemp cultivation is permitted, but also in establishing origins of seized drugs and, therefore, conspiracy in drug distribution networks. It also could be used in criminal defenses against claims of conspiracy.

Read more at UMN News.