• Some states prohibit employers from using a positive drug test as a reason for a negative employment action.
• A drug test for marijuana cannot indicate the effect the drug is having on an employee.
• Several factors impact a person’s degree of impairment from marijuana.
• A test that proves a person’s level of impairment from marijuana does not exist.

In states where marijuana is legal, a law may prohibit employers from using a positive drug test for marijuana as the basis for a negative employment action. Why is drug testing so controversial when it comes to marijuana use? It comes down to what the test can prove.

A drug test can show whether certain chemicals are present in a person’s body. The test can also detect whether a chemical’s metabolites, which are related to the chemicals, are in a person’s system.

A drug test does not measure the way someone is feeling or acting because of these chemicals. A positive test shows that marijuana has been used, but does not necessarily indicate anything about the effect the drug is having.

A person who uses marijuana will be impaired for three to 24 hours after using the drug, but determining whether a person is impaired a specific moment in time after using the drug currently can’t be proved by a drug test alone.

The degree of impairment from marijuana is going to depend on several factors, including:

• How the marijuana was ingested (vaped, smoked, or consumed in an edible),
• How a person is built and the amount of body fat the person has, and
• How often a person uses the drug.

Because marijuana is absorbed by the body’s fat and is slowly released into the bloodstream, a person who uses marijuana will test positive for the drug for a few days or even up to a month after it was last used, long after impairment wears off.

Why test for drugs and alcohol?

Because of the way marijuana is metabolized by the body, the amount of THC (the chemical in marijuana causing the high) measured by a drug test is not a consistent predictor of impairment. This may raise the question, why test for drugs and alcohol at all?

A drug test will show that a drug was used recently. Depending on what employers are testing for, a drug test can determine whether a person is using illegal drugs. It can certainly be a concern that a person has used an illegal drug recently.

If an employee is working in a dangerous position where impairment would cause a safety concern, testing may be warranted to support workplace safety.

In addition, a test for alcohol can prove that a person is impaired by alcohol. Alcohol is metabolized differently than marijuana and other drugs. There is a direct correlation between the amount of alcohol detected by a test and the degree to which a person is impaired by alcohol. A test for alcohol can accurately measure a person’s degree of impairment from alcohol use.

Tests are getting better at detecting recent use of marijuana, and tests that measure a person’s degree of impairment from marijuana use are under development. While there is currently no test that can determine whether or not a person is impaired on Monday after using marijuana on the weekend, it is clear that a person is impaired for several hours after using the drug. Marijuana use shortly before or during work time is reason for concern.

In some cases, federal law requires employers to test employees for drugs and alcohol. For example, drivers who are covered by Department of Transportation (DOT) drug and alcohol regulations are not allowed to use marijuana. They are tested for it, and face consequences if they test positive. When testing is required under federal law, an employer must adhere to those regulations and test employees for marijuana, even in states where marijuana is legal.