Benjamin K. Bishop, 18, of Oldsmar was arrested and charged early Sunday with two counts of first-degree murder, the Tampa Bay (Fla.) Times reported.
Pinellas Sheriff Bob Gualtieri said Bishop fired eight shots at his mother, Imari Shibata, 49, and her boyfriend, Kelley Allen, before 1:30 a.m. Sunday, before he called police and allegedly confessed to the crime.
Gualtieri said that Bishop, who is is unemployed and a diagnosed schizophrenic, and Shibata got into a fight on Saturday over the medication the teenager was taking.
"Apparently, Benjamin became very upset with his mother because he didn't like the medication," Gualtieri said. "He felt that the medication was killing him. So he decided that he was going to kill his mother and her boyfriend."
Bishop had a history of mental illness, addiction to bath salts and violence toward his mother, Gualtieri said.
In July 2011, the teen tried to strangle his mother. He pleaded guilty to battery charges and was given probation.