U.S. flag

An official website of the United States government, Department of Justice.

NCJRS Virtual Library

The Virtual Library houses over 235,000 criminal justice resources, including all known OJP works.
Click here to search the NCJRS Virtual Library

New Forensic Methods to Accurately Determine THC in Seized Cannabis

NCJ Number
Date Published
February 2024

This brief publication addresses the need for simple, cost-effective ways to identify the differences between hemp and marijuana, considering their different legal status and classification; it lays out basic details about hemp and marijuana and how most forensic laboratories have approached the substances, with discussion about impacts of direct analysis in real time-high-resolution mass spectrometry, or DART-HRMS, on sample analysis.


The Controlled Substance Act of 1970 classified the plant cannabis, which was historically classified as either marijuana or hemp, as an illegal drug, a Schedule I controlled substance with a high potential for abuse and no FDA-approved medical use in the United States. For almost 50 years, hundreds of thousands of people were arrested and imprisoned for possessing it. The Farm Bill of 2018 legalized the form of cannabis classified as hemp, while the form classified as marijuana remained illegal. The law left how to tell the difference up to law enforcement and forensic laboratories, which has proven difficult, time consuming, and expensive. Scientists use the amount of THC (one of the psychoactive components of cannabis) present in a cannabis plant to differentiate hemp from marijuana. The fact that many states have decriminalized the use of marijuana further complicates cannabis regulation. As a result of the Farm Bill, forensic laboratories must measure the exact amount of THC in seized evidence to differentiate hemp from marijuana. Thus, a new problem emerged for already backlogged crime labs. How could labs perform such precise measurements quickly and easily when few labs had the personnel, instrumentation, and protocols to do so? Two National Institute of Justice-supported labs addressed this problem using different types of mass spectrometry that can measure the exact amount of THC present in a sample: gas chromatography-mass spectrometry and direct analysis in real time-high-resolution mass spectrometry.