Massachusetts state police said they investigated 755 suspected heroin deaths in 2015 — but the death toll does not include cases in the Commonwealth's three largest cities, according to a published report.

Eighty percent of the overdose victims were men with an average age of 36, the Boston Globe reported.

Middlesex was the county with the most overdose deaths with 142.

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Boston, Worcester and Springfield, the three largest cities in Massachusetts, are not under the jurisdiction of the state police and were not included in the statistics. 

Halfway through 2015, there were 684 opioid-related deaths in Massachusetts, according to the Department of Public Health.

There were 1,256 opioid-related deaths statewide in 2014.