A Supreme Court judge has blamed Australia's most widely used antidepressant for causing a 76-year-old man to kill his wife of 50 years.

Justice Barry O'Keefe said David John Hawkins strangled his wife, Margaret, as a result of taking 250 milligrams of Zoloft - five times the recommended dose.

"The killing was totally out of character for the prisoner, inconsistent with the loving, caring relationship which existed between him and his wife and with their happy marriage of 50 years. I am satisfied that but for the Zoloft he had taken, he would not have strangled his wife," Justice O'Keefe said.

Justice O'Keefe sentenced Hawkins to a minimum of two years' jail, saying he was genuinely remorseful for killing his "soulmate" and was unlikely to reoffend. Hawkins has spent 22 months in jail and will be released on July 31 to live with his daughter and son-in-law at Wagga Wagga.

Yesterday medical experts defended the drug, saying it was a safe and effective treatment of depression.

"Generally speaking (Zoloft) is extremely safe ... but like all drugs that work in some situations, they are associated with unusual reactions," said Professor Ian Hickie, chairman of the national drug initiative, beyondblue.

Hawkins, a retired mechanic of Tumbarumba, in southern New South Wales, pleaded guilty to manslaughter on the grounds of diminished responsibility.

He first took Zoloft in 1996 after the death of his youngest daughter from breast cancer, and suffered an adverse effect after taking one tablet.

His depression returned in 1999 and Hawkins saw a different doctor who prescribed him Zoloft again.

The doctor told him not to take the medication until breakfast on Sunday morning, August 1, but he woke at 2am and took five tablets.

At 7.30am, as his wife prepared to light a fire, Hawkins strangled her with his hands. "I was looking at my wife but I wasn't seeing her face," he told a doctor.

Hawkins then attempted to kill himself.

A spokesman for Pfizer, which makes Zoloft, said there was no evidence to suggest the drug had any side effects of aggression or aggravation.

Pfizer lists more than 30 possible side effects inside boxes of Zoloft, including: agitation, anxiety, nervousness, abnormal thinking, lack of feeling and emotion, vomiting and twitching.

Zoloft came under intense scrutiny in the United States after the murder-suicide of actor Phil Hartman and his wife, Brynn Omdahl. Omdahl, 40, shot Hartman, 49, star of the TV sitcom News Radio and voice of several characters in The Simpsons, in 1998. She shot herself four hours later.

Her brother took legal action against Pfizer and a psychiatrist.