A Suffolk man was sentenced Thursday to five years in prison for distribution of fentanyl.

Eugene Tillery, 30, pleaded guilty in July after being indicted in May.

According to the indictment, from Nov. 14, 2015, through Dec. 2, 2015, the Drug Enforcement Administration, with assistance from the Suffolk Police Department, conducted a series of controlled purchases from Tillery, a press release from the U.S. Attorney’s Office stated at the time of his indictment.

The agents thought they were purchasing heroin from Tillery, but an analysis of the drugs by a laboratory revealed the drugs were fentanyl, which is a powerful painkiller that is 100 times more potent than heroin. Even a small amount of it can be lethal, according to prior press releases from the U.S. Attorney’s Office.

The agents made seven purchases from Tillery, totaling 26 grams.

Lacing heroin with fentanyl is a major reason for the alarming increase in thousands of deaths across the country from heroin overdoses, according to a press release this week announcing the sentence.

Tillery was also a major supplier of heroin in Suffolk, having distributed more than two kilograms of it during 2015, according to the press release.