Passive inhalation is sometimes put forward as a reason for a positive cannabis drug test result. Extensive Research has shown that this is improbable. As an example, in one study volunteers were exposed to smoke from cigarettes containing a known concentration of THC (the active ingredient of cannabis) over six one hour periods. The smoke was so intense that the volunteers had to wear goggles. The highest level detected by GC/MS analysis was only one third of the internationally accepted cut-off level for cannabis.
The International cut off levels for urine tests for THC (50ng/ml) are also set well above the level that could possibly be absorbed through passive smoking of THC fumes.