Twenty people have overdosed in Sacramento in less than a week, and a new, deadly drug combination could be to blame. Officials believe people are lacing the prescription painkiller Norco with fentanyl, a synthetic opiate, and the results are disturbing — five of the overdose victims have already died.

CBS Sacramento reported that health officials have issued a warning that those getting Norco prescribed from an illegitimate source are playing Russian roulette with their lives.

“People need to be aware that this is out there and some of the Norco that is being sold on the street is being contaminated, it is dangerous. It can easily cause an overdose,” said Dr. Olivia Kasirye, Sacramento County’s public health officer.

Drug counselor Jon Daily, from Recovery Happens outpatient treatment center, told abc10 he has treated many addicts.

“I’ve treated people who have abused pure fentanyl,” Daily said. “I never had clients using it mixed with Norco. I’ve been treating people with addiction since the mid-90s and this is new to me, this combination drug.”

Officials aren’t sure whether the contaminated pills are coming from one dealer or multiple ones. Either way, the drug they suspect is lacing the Norco pills is nothing to mess around with. Kasirye said fentanyl is much stronger and more potent than Norco, so it is the combination of the two drugs that causes the overdoses.

Poison control and first responders have both seen an uptick in calls. Crews rely on naloxone, a drug capable of reversing opioid overdoses, to help people. Though naloxone is usually very fast-acting, it’s hard for first response teams, like firefighters, to get. This is why health officials are working closely with police and hospitals to hunt down the source of the pills.

“It’s very important that people do not take pills from strangers, do not buy pills that are not prescribed to them, and that they need to be careful of the source of the medication that they’re taking,” Kasirye said.