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Passive smoke study undermines second-hand defense

Many managers of employee drug testing programs have heard employees who test positive for cannabis say that they were just in the room and inhaled passive or second-hand smoke. But those claims are undermined in a study published in May 2010 in the Journal of Analytical Toxicology.

The study exposed eight volunteers to passive cannabis smoke for three hours in a busy coffee shop in Maastricht, Netherlands. Beforehand, each volunteer provided a urine and blood sample. At specified intervals they provided additional urine samples up to 84 hours after exposure and blood samples up to 14 hours after exposure.

After immunoassay screening for cannabinoids and analysis using gas chromatography-mass spectrometry (GC-MS) for THC, THC-OH, and THC-COOH, the results were clear. Although all of the volunteers absorbed THC (the ingredient in marijuana that produces the high), the post-exposure samples showed only small concentrations.

The study’s conclusions: “Because none of the urine samples produced immunoassay results that were more than the cutoff concentration of 25 ng/mL, none of the passive inhalers would be misjudged for cannabis use during a routine drug screening. If GC-MS testing would be done nevertheless, the corresponding THC-COOH concentrations were below 10 ng/mL, even after hydrolysis. Furthermore, the results of this study indicate that passive exposure to cannabis smoke may only lead to trace amounts of THC in serum.”

To put it another way, the argument that passive cannabis smoke causes employees to test positive for marijuana use doesn’t hold water.*

* Results of this study cannot be applied to oral fluids results until it is replicated using oral fluids collections.

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