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WI DOJ Memo on Hemp or Marijuana: A new tool for law enforcement

Hemp or Marijuana: A New Tool for Law Enforcement

With changes to state and federal laws regarding hemp, it has become necessary for law enforcement to distinguish between hemp and marijuana. Hemp and marijuana cannot be distinguished by appearance, odor, or by the Duquenois-Levine color test commonly used to test for cannabis. A new field test known as the 4-AP test (also known as Cannabis Typification test) may assist law enforcement with this determination.

The 4-AP test cannot determine the concentration of the delta-9-tetrahydrocannabinol (THC). The results of the color test are based on the ratios of cannabidiol (CBD) and THC, two major cannabinoids found in the cannabis plant. A positive result for hemp (CBD rich cannabis) is a pink/red color. A positive result for marijuana (THC rich cannabis) is a blue color. When cannabis contains CBD and THC with neither cannabinoid being predominant in the plant material, a purple color may result and should be considered inconclusive.

To eliminate false positives with this test, it is recommended that a Duquenois-Levine test be performed prior to the 4-AP test. Follow instructions carefully, including using small amounts of plant material for the test. It will be beneficial to perform the 4-AP color test on a known sample of hemp and marijuana and familiarize yourself with the expected results. For more information, go to the Virginia DFS or Syndicate Chemistry websites listed below.

The 4-AP test was developed by the Forensic Institute of Zurich in 2017 and has been used since then by European law enforcement as a presumptive test to distinguish between hemp and marijuana. In 2019, it became available to US law enforcement with United States distribution. The Virginia DFS completed a study evaluating the 4-AP test and test kits provided by Syndicate Chemistry. The DEA has also incorporated the 4-AP test in their analytical scheme for cannabis. The WSCL has done preliminary evaluation of the 4-AP test/Cannabis Typification test kits. While this preliminary evaluation gave the expected results for hemp and marijuana, more investigation is necessary in order to incorporate the 4-AP test into our analytical scheme.




The 4-AP test or Cannabis Typification test may be purchased from Syndicate Chemistry. Ask about a law enforcement discount for the test. The WSCL is not involved in any endorsement of products from Syndicate Chemistry or any other company distributing the 4-AP test.


Prepared by Sandy Koresch – Controlled Substances Technical Unit Leader
Division of Forensic Sciences, Wisconsin State Crime Laboratories
Contact information koreschsm@doj.state.wi.us (414)382-7500


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  1. I also found this pdf called the Controlled Substances Unit FAQ’s and highlighted the hemp cannabis part below:

    Q: What is the difference between hemp and marijuana?
    A: The Cannabis plant is considered hemp by law if it contains less than 0.3% Tetrahydrocannabinol (THC). THC and Cannabidiol (CBD) are two major cannabinoids found in the Cannabis plant. In general, Cannabis will be classified as marijuana when the ratio of THC is much greater than CBD. Hemp and marijuana cannot be distinguished by appearance, odor, or the Duquenois-Levine color test.

    Q: Is there a color test available for hemp?
    A: Yes. Many companies have started distribution of products based on the 4-AP color test or cannabis typification test. This test may be a valuable tool to distinguish between hemp and marijuana based on the ratios of THC to CBD. However, it cannot determine a percentage of THC. For best results, perform the color test on known samples of hemp and marijuana to familiarize yourself with the appropriate colors.

    Q: Can the Crime Lab determine whether a sample is hemp or marijuana?
    A: The Crime Lab does not perform a quantitative analysis for the percentage of THC. However, analysis includes instrumental methods which can assess the levels of THC and CBD and may provide valuable information regarding whether the plant material is more consistent with hemp or marijuana.

  2. I feel this is a complete waste of time and resources in an effort to profit from cannabis users. The fact is cannabis is not a lethal drug and should be completely legal in the USA period.

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