A new research study has shown that secondhand marijuana smoke is highly unlikely to cause positive drug screen results, although in some cases this may be an issue. If an individual is exposed to large amounts of secondhand marijuana in a room that has no ventilation at all the I is possible for the individual to have positive drug screen results without actively smoking the drug, but only for 6-24 hours after being exposed. This is very rare according to John Hopkins University researchers who performed the study. The researchers used 6 participants who were experienced at smoking marijuana, and 6 participants who did not use the drug at all. There were 3 sessions, 2 were performed in a sealed room and the third session occurred in a well ventilated room. The non smoking participants were seated in the same room next to the marijuana smokers in each session.
The non smoking participants were tested at least 13 times during the 34 hours following their exposure to secondhand marijuana smoke, and only 1 individual in the study who did not smoke marijuana had positive drug screen results using the standard workplace testing methods. When a more sensitive drug test was used the researchers were able to detect very low THC levels in some participants but the positive results only occurred within 24 hours of exposure to secondhand marijuana smoke. Those who did not smoke and who were in a ventilated room did not come anywhere near the threshold required for a positive drug screen in the workplace.