Drug field test kits are so inaccurate, some places are banning them

The field test kits many law enforcement agencies use to determine whether a certain substance is an illegal drug while out in the field can be inaccurate. For that reason, they’re generally not admissible in court without some further testing or proof.

The results are considered preliminary – enough for an arrest but not reliable enough evidence for a conviction. The state must follow up with an official test by a crime lab or other expert testimony in order to present the evidence to a jury.

Nevertheless, the fact that the test kits are not accurate is extremely problematic. For one thing, the field test may be the only evidence available during plea bargaining. Defendants may have to choose whether to go to trial based on a positive field test that could easily be in error. That choice isn’t straightforward, even when you’re absolutely sure you didn’t have drugs in your pocket, car or residence.

About 99% of all drug charges are resolved by plea bargain, not trial. There is tremendous pressure from prosecutors to plead guilty. Defendants are usually given a choice: plead guilty to a lower offense or go to trial on a much more serious charge.

Also, a court may consider the positive field test when determining whether a defendant gets a bond. Without bond or with a higher bond, some people simply can’t afford to wait for trial. Some people plead guilty just to get out of jail.

Are drug field test kits too inaccurate to use even as a preliminary measure?

Yes. The stakes of an inaccurate drug test are too high. Completely innocent people have been arrested or even served time because they felt they had no choice but to plead guilty.

In 2016, the nonprofit newsroom ProPublica began publishing a series of articles about how inaccurate these field test kits are. Since then, a growing number of jurisdictions have begun disallowing their use altogether. Others are overturning convictions where a crime lab never confirmed the presence of illegal drugs – or when a person pled guilty and the crime lab later found no illegal drugs.

In the past 10 years, according to ProPublica’s latest follow up, at least 131 U.S. drug convictions have been overturned because no illegal drugs were actually found. Most of them came from Harris County, Texas, which analyzed a backlog of drug tests. The substances preliminarily identified as drugs were not, in fact, drugs in hundreds of cases.

How likely are false positive results with these field test kits?

According to testimony in a California case by an executive of the nation’s biggest manufacturer of field tests, false positives are extremely likely. He said his company maintains a list of over 50 legal substances that cause field test kits to test positive. For example, chocolate can read positive for heroin.

At their best, the results of drug field test kits are arbitrary. In fact, a federal judge in Massachusetts found in 2021 that NARK II brand kits’ results are “arbitrary and unlawful guesswork.” How high was the false positive rate? Fully 38%.

As a result, the Massachusetts Department of Correction can no longer use the kits to test prisoners’ mail and belongings. Unfortunately, prisoners had already been punished based on the results of NARK II kits.

It’s time to stop using these tests altogether.

The risk of innocent people facing arrest, charges and even conviction is just too high. Even false accusations can stain your reputation and result in an arrest record. As a society, we should not be relying on these tests, some of which have a nearly 40% false positive rate, for any reason.

Skip to content