A former North Texas pain management doctor was sentenced to 20 years in prison on Thursday for prescribing painkillers that contributed to the deaths of at least seven people in two states, according to reports.

Howard Gregg Diamond, whose office was in Sherman, north of Dallas, pleaded guilty to federal drug distribution charges in November.

The 57-year-old conspired with others to write unnecessary prescriptions for highly addictive drugs like fentanyl, hydrocodone and morphine.

Fox 4 reported that according to authorities, the overdose deaths occurred in the Texas cities of Abilene, McKinney and Sulphur Springs, and in the Oklahoma cities of Ardmore, Hugo, Idabel and Yukon.

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The Texas Medical Board suspended Diamond in 2017, the news outlet reported, saying he “posed a continuing threat to public welfare.”

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The Associated Press contributed to this report.