Massachusetts State Police report eight people have died in one week from a deadly strain of heroin known as “Hollywood” heroin. Officials say they are not sure how long the strain has been in the state.

The deaths were reported in small cities in Western Massachusetts, CNN reports. State officials say they are investigating why this strain of heroin is so deadly. There may be additional dangerous chemicals added to the batch, according to Holyoke Police Department Lt. Jim Albert. The strain may be so pure that even some people addicted to heroin can’t handle it, he noted.

A few people who used the deadly strain of heroin were saved by the opioid overdose antidote naloxone.

While police seized 9,000 bags of heroin with the “Hollywood” stamp and arrested four people on heroin trafficking charges, there still may be more of the heroin circulating, according to Springfield Police Sgt. John Delaney. He said it could have been passed on to other dealers, or it could have a different label. “Just like in all of New England, Springfield does have a heroin problem,” he said.

The Massachusetts Department of Public Health reported a 63 percent increase in opioid-related deaths from 2012 to 2014. The department said 1,089 people died during 2014 of opioid-related overdoses.

According to the Centers for Disease Control and Prevention, heroin overdose death rates increased by 26 percent nationally from 2013 to 2014 and have more than tripled since 2010, from 1.0 per 100,000 in 2010 to 3.4 per 100,000 in 2014.