CHARLESTON, S.C. — A 15-year-old boy who claimed the antidepressant Zoloft drove him to kill his grandparents was found guilty of murder Tuesday.

Christopher Pittman could get 30 years to life in prison after a jury rejected his claim that he was involuntarily intoxicated by the drug.

The trial has been billed as the first case involving a youngster who says an antidepressant caused him to kill, and it comes at a time of heightened scrutiny over the use of antidepressants among children.

Defence attorneys urged the jury to send a message to the country by blaming Zoloft for the killings. They said the negative effects of Zoloft are more pronounced in youngsters, and the drug affected Pittman so he did not know right from wrong.

"We do not convict children for murder when they have been ambushed by chemicals that destroy their ability to reason,'' attorney Paul Waldner said.

But prosecutors called the Zoloft defence a smokescreen, saying the then-12-year-old Pittman knew exactly what he was doing three years ago when he shot his grandparents, torched their house and then drove off in their car.