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Guilty Until Proven Innocent: Field Drug Tests and Wrongful Convictions

Field Drug Test Study

This year 773,000 people will be arrested based on field drug tests with known accuracy problems

NARK20033 reaction with Heroin

This report provides the first-ever comprehensive analysis of presumptive drug field test usage across law enforcement agencies in the United States. Inexpensive and fast, these tests have become a tool of choice for law enforcement agencies. Unfortunately, they are notoriously imprecise and are known to produce “false positives,” leading to frequent wrongful arrests and wrongful convictions.

Utilizing a nationwide survey of agencies, the report offers national estimates on the frequency of test usage, finding that each year approximately 773,000 drug-related arrests involve the use of presumptive tests. Although the true error rate of these tests remains unknown, estimates based on the imperfect data that are available suggest that around 30,000 arrests each year involve people who do not possess illegal substances but who are nonetheless falsely implicated by color-based presumptive tests. On a per capita basis, Black Americans experience these erroneous drug arrests at a rate 3x higher than White Americans.

While factors like eyewitness misidentification, false confessions, or prosecutorial misconduct have been previously cited as leading causes of wrongful convictions, these new results indicate that the use of presumptive field tests in drug arrests is one of the largest, if not the largest, known contributing factor to wrongful arrests and convictions in the United States.

View Report (Interactive)

View Report (PDF)

View Policy Brief (PDF)


View NBC News article

View Report (Interactive)


How Many Erroneous Arrests Are There In Your State?


How Can We Fix This?

Conduct Blind Audits

Conduct regular blind audits of cases involving presumptive testing to determine rates of false positives.

Use Accurate Methods

Use more accurate presumptive test that identify compounds by structural information (e.g. Raman spectroscopy) rather than simply by the presence of chemical groups.

Discontinue Usage

Limit or forbid the use of colorimetric presumptive field tests.

Adopt Cite-and-Release

Should field drug tests continue to be used in simple drug possession cases, adopt a cite-and-release policy to avoid the coercive effect of detention and its impact on wrongful convictions.

Require Confirmatory Testing

Require confirmatory testing whenever a guilty plea is accepted, with the right to withdraw the guilty plea following a no-controlled substance finding.

View the complete policy brief

Are you a public official interested in pursuing reform in your jurisdiction? Contact us.


A Real-World Example: Shai Werts

What’s that white stuff on your hood, man?
Werts: Bird (expletive).
Deputy: Bird (expletive)? That ain’t bird (expletive)!
Werts: I promise you, that’s bird doo-doo.
Deputy: I promise you, it’s not though.
Werts: I swear to God, that’s bird doo-doo.
Deputy: Well, I swear to God, it’s not. I just tested it and it turned pink.

In the summer of 2019, Georgia Southern quarterback Shai Werts faced cocaine charges after a deputy, using an error-prone field drug test, insisted bird poop on the hood of his car hood was drugs. Despite Werts’ repeated statements of innocence, he was charged, jailed, and subsequently suspended from the team. However, official lab results later cleared him of all drug charges, revealing the substance was indeed bird poop and not cocaine—highlighting the dangers of relying on unreliable field drug tests.


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