Tens of thousands of Americans may be wrongly arrested each year due to unreliable roadside drug tests, according to experts, as one state moves to curb the problem with new legislation.

Unusual cases have underscored the issue. Bird droppings scraped from a car have tested positive for cocaine. A toddler’s ashes were flagged as methamphetamine or ecstasy. And a great-grandmother’s prescribed medication triggered a cocaine result—setting off a 15-month legal ordeal that ultimately inspired a new law.

Colorado recently passed the first law in the United States prohibiting arrests based solely on colorimetric drug test results, a commonly used field-testing method among law enforcement.

These tests are widely used because they are inexpensive, portable, and capable of producing results within minutes. Sending every suspected substance to a laboratory would be costlier and could take days or weeks.

However, research from the University of Pennsylvania suggests these low-cost tools produce false positives at troubling rates.

While manufacturers have previously estimated error rates at about 4%, researchers believe the real figure may range from 15% to 38%. A separate investigation by New York City’s Department of Investigation found error rates as high as 79% to 91% in some correctional facilities.

“Innocent people are at risk of having their lives derailed by these inaccurate tests,” said Des Walsh, founder of the Roadside Drug Test Innocence Alliance.

What are colorimetric drug tests?

Colorimetric drug tests consist of small pouches filled with chemicals that change color when they come into contact with certain substances.

They typically cost between $2 and $10 and are used widely across the United States, Walsh said.

More advanced portable testing devices are available but cost significantly more—between $24,000 and $80,000—“hence the continued reliance on a $2 roadside drug test,” Walsh said.

The pouches contain chemicals designed to react with compounds found in drugs such as cocaine, methamphetamine, heroin, and fentanyl.

But many legal, everyday substances share similar chemical properties. “For example, the chemical characteristic of amphetamine has similar characteristics to the chemical compound for sugar,” Walsh said, explaining why sugar and substitutes can produce false positives.

Manufacturers themselves caution that the tests are only preliminary.

“NOTE: ALL TEST RESULTS MUST BE CONFIRMED BY AN APPROVED ANALYTICAL LABORATORY!” reads one warning label.

“The results of this test are merely presumptive,” it adds. “Reactions may occur with, and such compounds can be found in, both legal and illegal products.”

Despite those warnings, numerous cases show people being arrested based on these results.

From traffic stops to jail cells

In one case, former Georgia Southern University quarterback Shai Werts was suspended after a South Carolina traffic stop led to a cocaine possession charge. A deputy tested white residue on his car hood, which returned a positive result.

Werts contested the charge, and later lab analysis confirmed the substance—bird droppings—was not cocaine. His suspension was lifted, and the deputy later resigned.

In Illinois, police stopped Dartavius Barnes and tested the contents of a small urn in his vehicle. Officers initially suggested the ashes of his 2-year-old daughter were drugs. “I checked for cocaine, but it looks like it’s probably molly,” one officer said on body camera footage. Barnes pleaded, “No, no, no, bro. That’s my daughter.”

Lighting conditions, particularly at night, can make interpreting test results difficult, Walsh noted.

In Florida, Kena’z Edwards spent more than three months in jail after lidocaine in his car tested positive for cocaine. He was unable to pay a $178,000 bond, and lab testing was delayed until a trial date was set.

False positives are also common in correctional settings. Mail, paper, and ink can contaminate samples, and everyday items like soap, chocolate, and coffee have triggered positive results, Walsh said.

Even children have been affected. In Iowa, a 13-year-old girl was expelled after cookies she brought to school tested positive for THC in a field test. The treats were tested after another student fell ill, though the cause was unclear.

“It took her mom months to get a laboratory test that proved there was no THC or any illegal substance in the cookies at all,” Walsh said.

A case that prompted change

In Colorado, a 65-year-old great-grandmother’s experience became a turning point.

Holly Bennett was recovering from emergency surgery when a police officer entered her hospital room and accused her of possessing cocaine.

She had been suffering from “a bone infection from my cervical spine all the way down to my hips and pelvis,” she said, adding that surgery was needed because “my arms were getting paralyzed.”

“He said, ‘I’m with the Lafayette Police Department, and I’m here to issue you a ticket for possession of cocaine,’” Bennett recalled.

When she denied having drugs, the officer insisted otherwise. “He said, ‘Well, that’s what you had in your purse,’” she said.

Bennett maintains the substance was crushed prescription Ritalin. Hospital blood tests detected only her prescribed medications, not cocaine.

Still, she spent 15 months fighting the charge. She refinanced her home to cover legal expenses and repeatedly appeared in court without an attorney.

“I kept going to court without a lawyer,” Bennett said.

Prosecutors urged her to accept a plea deal involving a diversion program, which would erase the charge after completion but require time and money.

“Over 90% of people are taking a plea deal because they can’t afford to remain in jail” if they’re arrested after a positive colorimetric test, Walsh said.

Bennett even offered to pay $500 for independent testing, despite financial strain. “It would have been something that would hurt our ability to pay utilities,” she said.

At the time, lab testing in the state was delayed until cases were scheduled for trial, according to Boulder County District Attorney Michael Dougherty.

Eventually, Bennett secured legal representation, and lab results confirmed there was no cocaine. The case was dismissed, and records were expunged.

“They were wrong, and I was right,” Bennett said.

Policy shift and national implications

Dougherty acknowledged flaws in the system and said Bennett’s case highlighted the risks of relying on presumptive tests.

“With what we know now about the colorimetric field drug test, we’re going to be much more careful about whether the results that indicate it’s positive are accurate or not,” he said.

Her attorney, Noah Stout, said, “Everyone, at every stage, seemed to blindly trust the results of this test.”

“There’s a huge gap between the individuals who qualify for a public defender versus who actually can afford an attorney,” he added.

Colorado lawmakers, working with prosecutors, defense attorneys, law enforcement, and the Korey Wise Innocence Project, drafted legislation to address the issue.

Gov. Jared Polis signed the bill into law, making Colorado the first state to ban arrests based solely on colorimetric test results.

Under the law, additional evidence is required to support drug charges. For example, admissions by a suspect or other criminal activity could still lead to charges.

Supporters hope the measure will influence other states. Until then, experts warn that everyday substances—from vitamins to powdered milk—can still trigger false positives.

A costly but more reliable alternative

Experts say improved portable testing devices could reduce wrongful arrests.

While not as definitive as lab analysis, electronic testing tools are more accurate because they identify specific chemical signatures rather than broad characteristics.

Some police departments, including in Lafayette, Colorado, have begun using such devices. One unit cost more than $24,000, and officers are encouraged to use it for both accuracy and safety.

However, cost remains a barrier. Outfitting every patrol car with advanced equipment is impractical, and officers often rely on $5 field tests during roadside stops.

Walsh said colorimetric tests still have value as preliminary screening tools but should not be used as sole evidence.

He added that investing in better technology could ultimately save money by reducing wrongful arrests, court costs, and jail overcrowding.

“It helps reduce jail overcrowding. It helps reduce the cost of unnecessary prosecutions,” Walsh said. “Everybody benefits from more effective testing.”