The South Carolina Supreme Court upheld the murder conviction Monday of a teenager who claimed antidepressants led him to kill his grandparents and set their house on fire when he was 12 years old.

The court ruled against several arguments made by Christopher Pittman's attorneys, including the contention that he was denied a speedy trial before he was sentenced to 30 years in prison in February 2005. He was 15 at the time of his sentencing.

Three years earlier, he had shot his grandparents, Joe and Joy Pittman, with a pump-action shotgun as they slept, then set fire to their home in Chester County.

His attorneys argued unsuccessfully that he had been involuntarily intoxicated by the antidepressant Zoloft at the time of the shooting and didn't know right from wrong. In appealing, his attorneys said the trial judge should have used a different standard for jurors to determine involuntary intoxication.

Paul Waldner, one of Pittman's attorneys, said an appeal was possible.

"Obviously the decision is a setback for us, but our resolve to continue to try to obtain justice for this boy who committed the only violent act of his life only days after he was given a mind-altering drug is strong," Waldner said.

Prosecutor Barney Giese was not immediately available for comment.

The case generated outrage that Pittman was held so long before his trial. In October, dozens of supporters and relatives gathered in Columbia as defense attorney Andy Vickery argued before the state Supreme Court that his client's confession was influenced by Zoloft and his youth.

Pfizer Inc., the manufacturer of Zoloft, has said the drug "didn't cause his problems, nor did the medication drive him to commit murder."

Zoloft is the most widely prescribed antidepressant in the United States, with 32.7 million prescriptions written in 2003. In 2004, the Food and Drug Administration ordered Zoloft and other antidepressants to carry "black box" warnings -- the government's strongest warning short of a ban -- about an increased risk of suicidal behavior in children.

Christopher Pittman, now 6-foot-2, has attracted attention worldwide. He turned 18 in April and is in an adult prison, where supporters visit him regularly.