The federal agency responsible for testing defendants in the D.C. criminal justice system for drug use has begun testing for synthetic drugs, the agency announced Thursday.

For decades, the Pretrial Services Agency Office of Forensic Toxicology Services has tested arrestees and those on parole or probation only for cocaine, heroin, opiates and amphetamines. But as of Thursday, driven in large part by concern over their use in the District, the agency has added synthetic drugs to the list.

“We are not doing this testing to catch people but in order to help identify persons who may be having a problem in using these substances to correct their actions,” said Cliff Keenan, director of Pretrial Services. “This is a public health response as much as it is a criminal justice response.”

The new test will cost federal taxpayers about $3.50 a test, up from $1.60 before synthetic testing was done. The agency tests about 7,000 to 8,000 individuals a month, from new arrestees to those under supervision by a judge or a criminal monitoring agency.

District law enforcement agencies have raised concerns about the use of synthetic drugs across the city in recent months, particularly by those arrested for violent crimes. Until now, there was no standard testing for those arrested or on supervised released from jail or prison.

In July, a brief three-week study by the agency found that 20 percent of individuals arrested in connection with violent crimes tested positive for synthetic drugs. That is higher than the 13 percent who tested positive for PCP and the 13 percent who tested positive for cocaine.

Keenan said District officials first began noticing the use of synthetic drugs in 2012. At that time, the agency spent about $25 a sample to test arrestees for the drug at an outside private lab.

Also Thursday, D.C. Attorney General Karl A. Racine announced a new partnership with a Denver-based organization, the Coalition for Responsible Cannabis Production, in an effort to combat the rising use of synthetic drugs in the District and educate residents and businesses about the dangers surrounding the drugs.

In a statement, Racine said the goal of the collaboration was to reduce the use and accessibility of synthetic drugs.

“The manufacturers, distributors and sellers of these harmful synthetic drugs say the substances being peddled are a safe and legal alternative to marijuana,” Racine said. “Synthetic drugs are neither safe nor legal, and often include mysterious chemical compounds that present a range of potentially devastating side effects to users, from severe mental impairment and seizures to violent impulses and death.”