HOUSTON (AP) - The Houston Police Department says it will no longer have officers conduct field tests that give initial indications whether a substance is an illegal drug.

The tests have been criticized over the years for giving false positives in cases around the country. In Harris County, where Houston is located, the tests have led to wrongful drug convictions and exonerations after lab tests confirmed no illegal substances in many cases.

Police Chief Art Acevedo said Friday the change was made for safety reasons. Carfentanil, a synthetic opioid, was discovered in recent local drug seizures. Officials say the drug can be deadly if not properly handled.

Authorities say the change won't significantly affect how drug cases are prosecuted.

The Harris County Sheriff's Office also said Friday that it's stopping drug field testing.