Which questions arise following a “positive” drug test for Marijuana in the workplace? They may include “when was the drug last used?” and “does this mean my worker was ‘high’ at work”?

Keep in mind that the presence of THC in the blood or saliva does not necessarily equal impairment of a person. 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, the questions around risk management become 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 THC drug levels spike in the body very shortly following use. Following this spike, peak levels are reached rapidly. The drug levels then dissipate in both blood and saliva, following a rather uniform curve.

A marijuana user may be interested in the duration of the “detection window”. This is the period when marijuana can be detected in saliva by a drug test kit. The detection window depends upon the quality of the drug test kit and also the method of saliva collection.

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, say 100 to 200 nanograms per millilitre.

The level detected is sufficiently low to suggest Marijuana use occurred only within the last 14 hours, say 10 to 40 nanograms per millilitre.

Conclusions such as those above may be useful to establish risk levels for employees in the workplace.

Always remember, due to physiological 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.