Drug testing in the workplace is under the microscope as more employees are testing positive for state-legalized marijuana, either under recreational or medicinal use, experts say.

When it comes to workplace safety, the message to employers with workers in 29 states where marijuana is legal is: rethink testing and rewrite your policy, according to experts.

“You can’t deal with marijuana the same way you deal with alcohol,” said Mark Pew, senior vice president at Prium, a Duluth, Georgia-based medical cost management firm.

At issue is how long marijuana stays in a person’s system — weeks or more — when compared with alcohol and other drugs, which are typically excreted within hours.

Meanwhile, positive tests for marijuana use continued to climb in both federally mandated, safety-sensitive workplaces, such as transportation and nuclear plants, and general U.S. workforces, according to a study released in May by Madison, New Jersey-based Quest Diagnostics Inc.

In saliva testing, positive marijuana tests increased nearly 75% to 8.9% of the general U.S. workforce in 2016 from 5.1% in 2013.

Positive marijuana tests also increased in both urine testing — 2.5% in 2016 vs. 2.4% in 2015 — and hair testing —7.3% in 2016 compared to 7% in 2015 — in the same population.

Dr. Barry Sample, Seneca, South Carolina-based senior director of science and technology for Quest Diagnostics Employer Solutions, said the numbers were no surprise.

“We have been tracking increased use of marijuana,” he said, adding that states such as Colorado and Washington, where marijuana has been legal for recreational use for several years, saw some of the biggest leaps for workers in safety-sensitive jobs.

In that category, Colorado’s numbers jumped 27% from 2015 to 2016 and Washington state’s rose 19%. “We’ve been seeing increases in self-reported use; increases in our workforce data,” said Dr. Sample.

Expect the increases to continue, especially in light of the federal government’s latest hands-off approach to medical marijuana, experts say (see related story).

The implications for workplace safety remain to be seen, which leaves it up to employers to decide how to approach marijuana use, said Mr. Pew.

“It’s a very confusing message because presence does not equal impairment,” Mr. Pew said. “Just because you test positive for (marijuana) does not mean you are cognitively impaired.”

States differ on their approaches to intoxication and workplace accidents and some call for proving an intoxicated worker caused their injury for their workers comp claim to be denied, which is problematic when a positive marijuana drug test is submitted as the only evidence, experts say.

Sarah Sullivan, Denver-based risk control services coordinator for Lockton Cos. L.L.C., recommends that employers focus on better training for supervisors and employees on spotting whether an employee is intoxicated or high during the workday, and especially following an accident.

“You can’t solely rely on the drug test anymore so you are going to need to come up with training to recognize impairment so you can prove (it),” she said.

Ms. Sullivan published a white paper in May tackling the issue. For her research, she examined court records to gauge state positions on proving a worker was impaired at the time of an injury.

“A number of states are overturning drug test results saying the employer did not actually see them impaired at the time of the accident,” she said, naming courts in Louisiana and Georgia as among them.

Also at issue are pre-employment and random, unannounced drug tests as a way to maintain a safe workplace, said Mr. Pew.

“I have heard employers tell me that some are no longer doing pre-employment testing or have taken… marijuana off the panel because they can’t find enough clean candidates in the (job) pool,” he said. “Some say they will absolutely always test. There’s a weird pragmatic discussion that has to be had by each employer.”

Employers should consider what kind of work is being performed by their employees before testing for drugs, Mr. Pew said.

“If it’s a bunch of forklift drivers or those operating nuclear plants, none of your employees should be impaired,” he said. “However, if you are doing software development or customer service, does it hurt and can you find enough clean candidates to fill the position? Each employer has to make that decision for themselves.”

Ms. Sullivan offers similar advice to her clients. “Does (marijuana) affect what your employee is doing? You have to look at their job description.”

“I’ve heard some employers say that because the laws and the science are changing so quickly that they are removing the drug policy from the (human resources) manual,” said Mr. Pew. “I have always advised people that marijuana is so different… you have to have a separate policy.”