Analyzing the Impact of Adulterants on Marquis Presumptive Drug Tests

Presumptive Color testing is used in order to identify the potential presence or absence of a drug or drug class. This technique is especially useful for law enforcement to detect illicit substances during field tests due to their ease of use and portability (1). The Marquis color test is commonly used to identify opium derivatives, amphetamines, and other alkaloids, including fentanyl. Fentanyl is a rising threat in the US (2). For example, its presence in illicit drugs has contributed to 62.9% of 2024 overdose deaths in one US county (3). Drugs such as fentanyl are often cut with adulterants. These are drug additives, such as over the counter medications, which are used to increase supply and potency (4). This study aims to determine the impact of differing quantities of adulterants on the accuracy and interpretation of Marquis presumptive color test results. This was accomplished by testing diphenhydramine (active ingredient in Benadryl®) as a pseudo-fentanyl which was cut with various amounts of adulterants including acetaminophen, ibuprofen, quinine, and dextromethorphan. These samples were tested with the Marquis reagent, and the accuracy of the presumptive test results were evaluated after the color change. The results of this study indicate a need to re-evaluate the significance and use of presumptive color tests in fieldwork.