Can passive smoking cause a failed drug test?

Like tobacco smoke, cannabis fumes can be inhaled passively – and those exposed can experience the effects of cannabis. Dr. Evan Herrman and his team of researchers demonstrated in 2015 that:

‘Under extreme, unventilated conditions, second-hand cannabis smoke exposure can produce detectable levels of THC in blood and urine, minor physiological and subjective drug effects, and minor impairment on a task requiring psychomotor ability and working memory.’

THC is known to be the main cannabis constituent responsible for its psychological effects and one of the three cannabis constituents tested for in forensic hair analysis. A further test for the THC breakdown product; 11-Nor-delta9-THC-carboxylic is also undertaken.

As, following passive inhalation, the constituents may be detected in the blood – and therefore incorporated into the hair follicle. This leads to the possibility that those not actively using cannabis may test positive for THC and other constituents albeit at very low levels, and rarely above the cut-offs.

This has not gone unnoticed by those wishing to disprove a positive test and the ‘get out of jail card’ of ‘I have been in the company of other users’ is a well-worn path.

How we can tell the difference between cannabis consumption and passive inhalation?

As it has been shown that the breakdown product of THC; 11-Nor-delta9-THC-carboxylic does not form in significant amounts after passive inhalation it will not be detected above the cut-off for a positive test and therefore those testing positive for this metabolite are active users.

“Cannabis constituents are usually only detected at low levels when regular passive inhalation occurs. The THC metabolite; 11-Nor-delta9-THC-carboxylic Acid is not detectable above the cut-off when cannabis is inhaled passively. BUT the presence of 11-Nor-delta9-THC-carboxylic Acid is not required to prove cannabis misuse.” Dr. C Pyves

It is important to note that whilst the presence of this metabolite alongside other constituents at significant levels is strong evidence for use, its absence does not confirm passive smoking.

This means that by determining the presence of the metabolite 11-Nor-delta9-THC-carboxylic Acid, we can determine whether or not someone has actively consumed cannabis.

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