In an era where drug testing plays a major role in employment, law enforcement, and public safety, it’s important to separate science from assumption. Oral fluid drug tests, while convenient and widely used, are often misunderstood — especially when it comes to cannabis. The truth is simple but significant: Mouth swab drug test can show whether someone has used cannabis recently, but they cannot prove that the person is impaired.

The Problem with Testing for THC in Saliva

When someone uses cannabis, THC (the psychoactive ingredient) can be deposited in the mouth and absorbed into the bloodstream. Saliva tests detect the presence of THC or its metabolites in oral fluid. These tests are useful in confirming recent use — typically within a day or two — but they do not indicate how much was used, how long ago it was used, or whether the person is still experiencing any impairing effects.

That’s because THC does not behave like alcohol. With alcohol, blood or breath concentration correlates closely with impairment. Not so with cannabis. THC is fat-soluble, meaning it gets stored in body fat and released gradually over time. This makes the timing of impairment nearly impossible to determine from a saliva sample alone.

Positive Test ≠ Impairment

Imagine someone legally using cannabis in the evening to relax or manage a medical condition. By the next morning, the impairing effects have worn off — yet they may still test positive on an oral fluid test. That person is not impaired, but the test result could cost them a job or trigger legal consequences.

This is not just hypothetical. Studies have consistently shown that THC levels in saliva do not reliably match up with how impaired someone actually is. In other words, a person can fail a saliva test and be perfectly capable of driving or working safely — or pass a test and still be impaired, especially if they’re an infrequent user with low residual THC.

Scientific Consensus Is Clear

Leading researchers and public health agencies agree: no current test can accurately measure real-time cannabis impairment the way breathalyzers can for alcohol. As a result, relying on oral fluid tests as proof of impairment is not only flawed — it’s unfair.

A Call for Smarter Policy

As cannabis use becomes more common and accepted — both medically and recreationally — the systems used to monitor and regulate it must catch up. Oral fluid drug tests have their place in identifying recent use, but they should never be used alone to judge whether someone is impaired. That requires a more holistic, evidence-based approach that considers behavior, context, and validated impairment assessments.

Conclusion

Oral fluid drug tests cannot measure cannabis impairment. They detect presence, not effect — and that difference matters. It’s time to move beyond outdated assumptions and ensure that drug testing practices reflect real science and protect people’s rights.