Drug use among American workers has dropped dramatically over the past 25 years, but certain drugs—particularly prescription medications--continue to be abused in the office, according to a new analysis from Quest Diagnostics.

The diagnostic information services firm reports that drug use among American workers has dropped by 74% in the past quarter century, according to data from more than 125 million workplace drug urine tests. The study evaluated  the annual positivity rate for employees in positions subject to certain federal safety regulations, such as truck drivers, train operators, airline and nuclear power plant workers and those from the private sector.

Quest reports positivity rates for amphetamines, including amphetamine and methamphetamine has nearly tripled (196%higher) over nearly 15 years and hit the highest level in 2012. For amphetamines, including prescription medications like Adderall, the positivity rate has more than doubled in the past decade among workers.

Positivity rates for opiates, including hydrocodone, hydromorphone, oxycodone and oxymorphone have increased. Quest reports oxycodone usage in particular is up 71% from 1998 to 2012, which is reflective of nationwide prescribing trends, says registered Nurse Ronald Todaro, who says the report jibes with the thousands of annual pre-hire assessments the hospital conducts for open job positions.

“Over the past few years, we have seen a downward trend in the abuse of substances like cocaine and marijuana, but an upward trend with prescription medications,” says Todaro, who also serves as director of Corporate Health at University Hospitals Case Medical Center. “The highest group of positive tests are for central nervous system stimulants like Adderall, and the second highest group are those testing positive for anti-anxiety drugs like Valium.”

However, if a candidate has a proper prescription for the drug, that won’t prevent them from being hired,  Todaro says. “The users are taking them legally, but there is an increase in physicians and practitioners prescribing these people,” he says.

The tables may turn in the future, Todaro says, as more prescribers are being “tested” as to why and how they are deciding who needs what medication.

“Anyone who is prescribing medications is being challenged more and more to not write them so liberally,” he says. “In the past, you could just write a prescription and let it go. “

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