What Is a Toxicology Test?

Medically Reviewed by Carol DerSarkissian, MD on May 28, 2023
3 min read

A toxicology test (drug test or “tox screen”) looks for traces of drugs in your blood, urine, hair, sweat, or saliva. You may need to be tested because of a policy where you work or go to school. Your doctor could also order a toxicology test to help you get treatment for substance abuse or keep your recovery on track.

A toxicology test can’t show if you have an addiction problem. It also can’t pinpoint how much of a drug you’ve used or when. It’s only able to tell if certain drugs are (or have recently been) in your body.

Long after you inhale, inject, or ingest them, legal and illegal drugs leave clues in your body. Traces of opiates are still in your urine a few days after you take them. Signs of marijuana can last up to 3 weeks.

A toxicology test can screen for:

There are different reasons that you may need to have a drug screen. Your new job, school, or insurance policy could require it. Many sporting programs expect players to have one.

Your doctor may also order this test if you:

  • Are in treatment for drug addiction
  • Show signs of substance abuse
  • Have problems with your mental health
  • Have been taking a controlled drug for a long period of time

A drug test can also be ordered for legal reasons. You may be required to take one if you’ve been accused of a crime. The same goes for many people who are on parole.

Most of the time, a sample of your blood or urine will be tested. Blood is drawn from a vein in your arm or you’ll be asked to pee into a cup. The sample will then be tested at a lab.

Sometimes, sweat, a strand of hair, or saliva from your mouth is used instead of blood or urine. In extreme cases, other body fluids are checked. If your stomach is pumped at the hospital, a sample of your stomach contents may be tested.

Before your test, let your doctor know what drugs you’ve taken in the past few days. Make sure to include over-the-counter medicines and supplements. Some of them can show up in your system like other drugs and cause a “false positive” on your test.

Depending on the type of test you have, you should get your results within 24 to 48 hours.

Your test will come back with one of two results:

Positive: At least a trace of one or more drugs was found in your sample. If this happens, another test is done to confirm the result. This second test is more precise and can identify the type of drug.

Negative: No drugs were found in your system. This could be because you’ve never taken the types of drugs the test was looking for or, if you have, your body has already processed them.

Some products claim they can help you pass a drug test, but there’s no proof any of them work. If you know that you’re going to be asked to take a toxicology test, your best bet is not to use drugs. If you do use them, your doctor can give you advice on how to stop.