We get this question a lot. Parents, donors, employers and even panicked potential employees call our after hours line to ask how far back can a test detect drugs.

The answer? “It depends.”

It depends on the drug, the drug test method, the user’s body and frequency of use. It also depends on something called a “cut-off level.”

The urine drug test is the “gold standard” for drug testing.  But hair and oral fluid testing are becoming more and more common, and each has its strengths as well as limitations, and each has a different detection window.


Since the Federal Drug-free Workplace Act launched drug testing as an industry in 1988, urine has been the standard. It is an inexpensive, easy-to-perform drug test and is non-invasive. It is also currently the only method permitted for federally mandated testing.

Most drugs will test positive in urine for 2 to 4 days after use. Marijuana is the exception and can be detected for 30 days or more in a heavy user.

One of urine drug testing’s drawbacks is that it’s possible for a donor to cheat the drug test. Type “How to cheat a drug test” into your favorite search engine and you will find all kinds of products, kits and techniques that may or may not work.

Many users will abstain long enough to pass a pre-employment drug test, but go back to using later.

We know. They come to us to make sure they test clean.

Experienced drug test collectors are trained to reduce the likelihood that a cheater might get through. Short of going into the bathroom with them, all reasonable precautions are built into the process. But some will inevitably succeed.


Hair testing is growing in popularity. Most specimens will provide 90 days of history, which helps explain the higher (9.6%) positive rate. Nearly impossible to cheat, hair testing is designed to detect habitual use, so may not catch a one-off.

Of course, not everyone has enough hair on the head, so body hair can be used too. And since the hair is cut close to the skin, you really aren’t testing for the most recent 5 days or so. For that reason, some companies will test hair in addition to urine or oral fluid, so they can get as much coverage as possible.

At InOut Labs we do a lot of hair tests, and it’s rare we cannot get enough hair from a donor.

Oral Fluid

Oral fluid testing is growing in popularity because it is easy to administer and very difficult to cheat.

Its shorter window of detection (especially for marijuana) makes oral fluid testing a really good choice for suspicion or post accident testing. Despite the shorter detection window, the positive rates are higher than urine tests (7.7% vs. 4.7% for urine).

Drawbacks are that there is a cost for the testing device, and there is no generally available way to collect a split specimen. Lab fees are higher too. As those costs come down, expect to see more oral fluid testing.

What about blood?

Blood is not used for employee drug testing for several reasons. It’s expensive and invasive, and, counter-intuitively, it’s not very useful. Drug metabolites leave the blood in a matter of hours. In fact, a person may still be feeling the effects of the drugs and have a negative blood test.

For more information on drug testing for your company, contact InOut Labs.

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