PONTIAC, Mich. (AP) _ A man who said the sleeping pill Halcion drove him to shoot his wife to death was found innocent by reason of insanity.

John Caulley admitted donning a mask and ambushing his estranged wife, Kathleen, outside their Troy home in 1988. The 44-year-old former stockbroker had started taking the prescription drug three months earlier.

Critics have said Halcion can cause serious side effects, including short- term memory loss, violent behavior and hallucinations. The federal Food and Drug Administration concluded in 1992 it was safe and effective when used as directed.

Caulley was convicted of first-degree murder in 1990. The Michigan Court of Appeals ordered a new trial in 1992, saying the jury should have been instructed to consider the effects of Halcion in its deliberations.

Friends of Ms. Caulley were angered by the Oakland County jury's verdict on Wednesday.

''He was threatening her with a gun all the time,'' Bill Naschak said. ''This was before Halcion, this was before all those things. He had been abusing her.''

Caulley was being held Wednesday at the Center for Forensic Psychiatry in Ypsilanti. He will be evaluated in 60 days and may be released if doctors are satisfied with his condition.

''He was grateful to the jury,'' said Caulley's attorney, David Lawson. ''He told me he cries every night about his wife.''

Kaye Bennett, a spokeswoman for the Kalamazoo-based Upjohn Co., said millions of people have safely taken the drup worldwide in the past decade.

''There is no evidence that Halcion caused the kind of behavior that was claimed in this case,'' she said.

Halcion was approved for use in the United States in 1982. It has since been banned in Europe.

In 1992, a Texas jury awarded $2.15 million to the family of a man who said Halcion altered his personality and made him kill a friend. The jury divided the blame between the assailant and Upjohn.