• Kelly Knight

Marijuana v. Hemp

Updated: Jul 20


#FORENSICFRIDAY: Both marijuana and hemp come from the same plant species (Cannabis Sativa), however they have several differences that make them distinct, both genetically and chemically.



Marijuana is cultivated for use as a psychotropic drug. It generally has high levels of tetrahydrocannbinol (THC), which is the psychoactive component.


Hemp on the other hand is cultivated for use in products such as foods, personal care, nutritional supplements, etc. and has much lower levels of THC (<5%).


The Farm Bill

According to the 2014 Farm Bill, hemp was considered a schedule 1 controlled substance. In 2018, however, hemp was removed from the definition of marijuana, meaning it is no longer a controlled substance. Legally, the THC threshold for defining hemp is no more than 0.3% on a dry weight basis.


For forensic labs, this created a bit of a nightmare. They have now had to change their analytical schemes to not only detect THC but now they have to know exactly how much THC is there because it is considered legal as long as the concentration is no more than 0.3%.


Forensic Chemistry Analytical Schemes: Old vs. New

An analytical scheme in a forensic chemistry lab is generally broken up into three parts: 1) A macroscopic/microscopic examination of the substance in question 2) A color test and 3) Analysis & identification using a separation & detection technique such as thin layer chromatography or gas chromatography/mass spectrometry.


One change the DEA has made, for example, is they are now using a new color test. Previously, their laboratory used the Duquenois-Levine test which is a screening test for marijuana. They are now using the 4-aminophenol test which gives an indication of the THC concentration (swipe to see what it looks like). A blue color result indicates that the THC concentration is higher than the concentration of cannabidiol (CBD, the active ingredient in hemp). These samples would undergo further analysis to assess the exact level of THC present to determine whether it was legal or not.


📸: Surterra Wellness

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© 2020 by Kelly Knight