Four people are in police custody in connection with the investigation into a pair of drug overdoses linked to one home in south Cambridge.

In one case, police say, a person lost their vital signs and was revived thanks to a bystander and a police officer performing CPR.

Police believe both overdoses were caused by drugs purchased at a home on Crombie Street.

“We believe that the substance that they were ingesting was Fentanyl,” said Staff Sgt. Paul Lobsinger, who added that the overdose victims may have thought they were taking other drugs without realizing the narcotics had been laced with Fentanyl.

“We realized quite quickly that we needed to stop this to avoid any further medical issues in our community.”

After learning of the alleged link to the house on Crombie Street, police moved in and arrested four people found inside – two men and two women.

Officers again entered the home Thursday morning, were they seized illicit drugs and prescription pills, as well as bicycles and a credit card believed to have been stolen.

The four people arrested, all Cambridge residents, now face charges of drug possession for the purpose of trafficking.

Lobsinger says illegal drugs being laced with Fentanyl – sometimes without the people taking the drugs realizing it – is an increasingly common and potentially deadly scenario.

“They think they’re ingesting one type of (drug), when in fact they’re ingesting something much more potent,” he said.

With reporting by Leena Latafat