NORTHAMPTON, Mass. (AP) -- A former chemist pleaded guilty on Monday to stealing drugs from a state crime lab in a case prosecutors said led to the dismissals of more than 200 drug cases.

Sonja Farak pleaded guilty in Hampshire Superior Court to theft of a controlled substance, tampering with evidence and drug possession, Attorney General Martha Coakley announced. The 35-year-old Northampton resident was sentenced to 2 1/2 years in prison, with 18 months to serve and the rest suspended during a five-year probation.

Farak was arrested in January 2013 after co-workers at the Amherst lab reported that drugs were missing.

Prosecutors said Farak tampered with four drug samples stored at the lab, in two cases mixing the drug evidence with counterfeit drugs to hide her thefts. They said cases were dismissed because Farak couldn’t testify about the results of her drug testing.

The Daily Hampshire Gazette reported the judge told Farak in court her conduct "clearly has eroded everybody’s confidence" in the crime labs, which can affect people’s lives and liberties.

Defense attorney Elaine Pourinski asked the judge to sentence Farak to four years of probation, saying she struggles with drug addiction and mental health issues, the Gazette reported.

"She is here to take responsibility," Pourinski said. "She doesn’t blame anyone else. She blames herself."

Farak’s case is not connected to that of former chemist Annie Dookhan, who worked at a state drug lab in Boston. Dookhan pleaded guilty to faking test results in criminal cases to make herself look more productive. She was sentenced in November to at least three years in prison. State officials said she jeopardized thousands of convictions.