Some of the first questions arising following a drug test which is “positive” for Marijuana in the workplace are “when was the drug last used?” and “does this mean my worker was ‘high’ at work”?

It is important to keep in mind that the presence of THC in the blood or saliva does not necessarily equal impairment of a person. However, from a risk management perspective the key distinction here is that the presence of THC may represent a risk – and that risk should be managed. So a worker may not be ‘high’ but it is best to err on the side of caution.

When using saliva drug testing, instead of urine, this question becomes a little easier to answer.

A number of research studies have demonstrated that THC is detectable in saliva for somewhere between 10 to 15 hours. We also know that very shortly following use of THC the drug levels spike in the body. Following this spike and reaching the peak levels, they levels dissipate in blood and thus saliva, following a rather uniform curve.

A marijuana user may be interested in the detection window, that is the timeframe during which marijuana can be detected in saliva by a drug test kit. The first answer to this question is – “it depends upon the quality of the drug test kit and also the method of collection”. Secondly, the answer requires analysis of drug levels found in saliva following use of marijuana.

Data from such research may allow conclusions such as below:

The level detected is sufficiently high to suggest Marijuana use occurred within the last several hours.

The level detected is sufficiently low to suggest Marijuana use occurred within the last 14 hours.

Conclusions such as those above may be useful to establish the level of risk associated with drug use of a particular employee in the workplace.

However, due to variables and the limits of science available it is not possible to provide a definitive answer which defines exactly when THC was consumed and how much.