A study recently published in the Journal of Analytical Toxology suggests that those who have an upcoming drug test might need to watch out – second hand marijuana smoke can cause a positive result. After concerns about the effect of second-hand smoke increased with the stronger potency of cannabis available, researchers at John Hopkins University conducted a study to determine the effect that sitting in a room full of pot smokers can have on non-smokers in terms of drug test results.

Six non-smokers sat in a chamber with six pot-smokers who had joints of different strengths in a number of different sessions. In some, the chamber had no ventilation and in others, the chamber had some ventilation. The non-toking participants tested positive for THC (the magical substance in pot) for up to 22 hours after their time in the chamber.

It’s important to note, however, that the drug testing measures used in the study were more in-depth than standard workplace drug tests. In addition to the rigorous tests for the purposes of the study, standard workplace urine tests were done as well. Out of all the standard work-place tests done on the non-smoking participants, only one yielded a positive result, and that was only four hours after their time in the chamber. What this means is that while you may have THC in your system after hanging out with smoking friends, it probably won’t show up on your upcoming drug test.

Other factors influencing drug tests…

THC binds to fat, which means that a higher BMI (or being on the rounder side) means that you’ll test positive for THC for a little longer than those with a lower BMI. The participant who tested positive on the standard workplace test had a higher BMI than other participants. Ventilation is also an important factor – sitting in an air locked car with a couple of pot-smoking friends is more likely to lead to a positive result than sitting in a living room with the window open. The potency of the cannabis is also an important factor – participants tested positive for longer after being in a chamber with high-potency cannabis smokers than those who had been in a chamber with low-potency cannabis smokers.

Does this mean staying away from fellow tokers in the lead up to a drug test?

Unless you have a workplace drug test within the next couple of hours, or your workplace uses ridiculously strict testing methods, there’s probably no real need to worry. Staying in a well-ventilated room won’t hurt, but, as the study concluded, there’s no real need to worry.

Parker Winship