By Sandra Gonzalez, CNN

(CNN) -- Chris Cornell's doctor is to blame for the Soundgarden singer's death, his family states in a lawsuit filed Thursday.

Dr. Robert Koblin "negligently and repeatedly" prescribed "dangerous mind-altering controlled substances" that impaired Cornell and "caused him to engage in dangerous impulsive behaviors that he was unable to control, costing him his life," according to the lawsuit obtained by CNN.

The lawsuit was filed in Los Angeles Superior Court.

The rock star had a history of substance abuse and chemical dependency. His family claims that Koblin prescribed Cornell more than 940 doses of lorazepam (also known as Ativan) during the last 20 months of his life.

"Yet, at no time during this period did Dr. Koblin conduct a medical examination of Mr. Cornell, perform any laboratory studies, obtain an interim history or do any type of clinical assessment of Mr. Cornell," the suit states.

Cornell, 52, died in May 2017. The official autopsy results ruled the cause of death as suicide by hanging.

Koblin's attorney said the prescriptions were appropriate.

"Dr. Koblin is a competent and conscientious doctor who enjoyed an excellent physician/patient relationship with Mr. Cornell and other members of his family," James Kjar said in a statement Thursday evening. "The experts I have consulted with believe Dr. Koblin's treatment was within the standard of care in this community and were not a substantial factor in causing Mr. Cornell to commit suicide."

In June 2017, a toxicology report revealed Cornell had several prescription drugs in his system. Those included lorazepam, a tranquilizer used to treat anxiety by slowing brain activity to allow relaxation, according to the US National Library of Medicine. Lorazepam can be habit-forming.

Cornell's widow, Vicky Cornell, who is among those who filed the suit, had disputed that Cornell's death was intentional.

"I know that he loved our children and he would not hurt them by intentionally taking his own life," she said in a statement in May 2017.