Opiate use among Hawaii workers dropped 50 percent during the first quarter of this year compared with the same time last year, according to workforce drug tests performed by the state’s largest laboratory.

“This could be the result of the U.S. Department of Transportation’s announcement that they would begin testing for certain opioids,” Steven Brimmer, Diagnostic Laboratory Services’ scientific director of toxicology, said Tuesday.

The Department of Transportation gave notice last year it would begin testing on Jan. 1 for the semisynthetic oxycodone, hydrocodone, hydromorphone and oxymorphone. These are commonly known as OxyContin, Percodan, Percoset, Vicodin, Lortab, Norco, Dilaudid and Exalgo.

“Workplace testing does work,” Brimmer said. “Basically, the whole idea to me is that you let people know what they’re going to be tested on, and they stop doing it.”

While the recent broadening of the DOT’s testing standards may have affected the drug test results from all Hawaii workers, they only pertain to airline pilots, ship captains, helicopter pilots, drivers of large trucks and others who fall under the agency’s standards.

DLS collects urine samples for the DOT but does not perform the testing.

Opiate use fell to 0.2 percent from 0.4 percent in the year-earlier period.

In contrast, cocaine use doubled to 0.4 percent from 0.2 percent, and amphetamine use was up 33 percent during the first quarter to 0.8 percent from 0.6 percent.

Marijuana use rose 20 percent to 3 percent from 2.5 percent.

Synthetic urine, which is used to hide drug use, was unchanged at 1.2 percent.

“THC (marijuana) is almost always No. 1,” with the highest percentage of positive confirmed results, followed by synthetic urine and amphetamines, Brimmer said.

DLS’s sample size typically includes 7,000 to 10,000 drug tests.