CHARLESTON, S.C. ? A 15-year-old boy who claimed the antidepressant Zoloft drove him to kill his grandparents and burn their house down was found guilty of murder Tuesday and sentenced to 30 years in prison.

The jury took six hours to reject Christopher Pittman’s claim that he was “involuntarily intoxicated” by the drug and could not be held responsible for the crime.

The case was one of the first of its kind to come to trial in the United States since the government began taking a close look at the dangers of antidepressant use among teenagers.

Pittman was 12 in 2001 when he killed his grandparents, Joe Pittman, 66, and Joy Pittman, 62, with a pump-action shotgun as they slept in their rural home, then torched their house and drove off in their car. He was charged as an adult.

About a month before the slayings, Pittman was hospitalized after threatening to kill himself. He was prescribed the antidepressant Paxil and was later put on Zoloft.

A psychiatrist testified for the defense that the Zoloft was to blame for the killings.

Zoloft is the most prescribed antidepressant in the United States. In October, the Food and Drug Administration ordered Zoloft and other antidepressants to carry “black box” warnings about an increased risk of suicidal behavior in children.