SHERMAN, Texas (AP) — A Texas doctor wrote unnecessary prescriptions for powerful drugs that contributed to the overdose deaths of at least seven people over a four-year period, according to a federal indictment unsealed Wednesday.

Howard Gregg Diamond, 56, was arrested Tuesday on charges that include conspiracy to distribute controlled substances and health care fraud.

Prosecutors contend that Diamond began issuing prescriptions in 2010 that had no legitimate medical purpose. The prescriptions were for drugs such as fentanyl, hydrocodone and morphine, according to the indictment.

Authorities...