Most drug tests given to people on parole or probation are unlikely to detect synthetic marijuana, a new study finds.

The Washington Post reports the study found that among a sample of young men from the Washington, D.C. parole and probation system, 39 percent tested positive for synthetic marijuana, even though they had passed a traditional drug screen.

The study was conducted by the White House Office of National Drug Control Policy (ONDCP) and the University of Maryland’s Center for Substance Abuse Research. The researchers said the findings underscored the need for updated testing.

The report stated, “For the first time we, found a drug that was as likely to be found in persons who had failed the limited criminal justice system screen as in persons who had passed.”

“Most drug tests are testing for the old epidemics, and they need to update their panels,” said lead researcher Eric Wish. “This is not only for the criminal justice system but the public health system as well.” People who undergo routine drug screening in the workplace, such as hospital workers and military personnel, could also be using synthetic marijuana without getting caught, the article notes.

“You have people coming into these places exhibiting strange behaviors and they enter the public health system looking for help, but the doctor may not know what is wrong with the person,” Wish said. “The public health system needs to start looking at these new metabolites to screen for them.”

Rafael Lemaitre, Associate Director for Public Affairs at the ONDCP, said the agency hopes the findings will encourage officials at the state and local level to stay on top of synthetic drug trends.