What Is a Drug Test Patch?

Read about how sweat-absorbing skin patches detect drug use.

By , Attorney · University of San Francisco School of Law

Drug testing is an important component of the criminal justice system. And there are lots of ways to detect drug use. Some law enforcement agencies are now using drug-test patches as an alternative to more traditional methods like blood, urine, and hair-follicle testing.

How Drug-Test Sweat Patches Work

When a person takes drugs, a small amount will eventually come out in the person's sweat. Typically, traces of a drug will start to appear in sweat within a day or so of when a person uses. It will then be several more days before the person's sweat will be clear of the drug.

A drug-test patch adheres to a person's skin like a Band-Aid. The inner part of the patch that contacts the person's skin has an absorbent pad that soaks up perspiration. If there are drugs in the person's sweat, the patch absorbs those as well. So when a drug-test patch is removed, it should contain samples of all the drugs the person took and sweated out while wearing the patch.

How Long Do You Have to Wear a Drug-Test Patch?

Normally, a drug-test patch is worn for a week or more. The defendant first goes to a testing center where a worker affixes the patch to the defendant's shoulder. About a week later, the defendant returns to the testing site and a worker removes the patch. The center then sends the patch to a laboratory for analysis. The laboratory reports back with the results.

Can the Sweat Patch be Removed?

To thwart efforts to conceal drug use, drug-test patches are designed so that once removed, they can't be reattached. Each patch also has a unique number that the testing center records when putting on the patch; if the defendant uses drugs, then tries to switch out for a different patch, the testing center will know because the patch the defendant comes back with will have a different number.

Which Drugs Patches Detect

Drug-test patches can be used to test for a number of different drugs. (Other methods such as SCRAM bracelets are often used to monitor alcohol use.) The U.S. Food and Drug Administration (FDA) approved drug patches for identifying use of:

  • marijuana
  • cocaine
  • opiates
  • amphetamines/methamphetamine, and
  • phencyclidine (PCP).

Though other methods exist for detecting these drugs, patch testing has certain advantages. For example, patches have a wider detection window than urine and blood testing. Many drugs will clear a person's system within a few days. So, if a person who uses a fast-clearing drug isn't urine or blood tested within a few days, no one will know about the use. Drug-test patches, on the other hand, continuously collect and store evidence of drug use while the patch is on. This feature cuts down on the frequency of testing necessary to ensure a defendant remains drug-free—for the week (or another time period) the patch is on, the court can be fairly certain that any drug use will be detected.

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