Alcohol and drug misuse means Scots are almost twice as likely as people south of the border to take their own life or kill, a new report has said.
Research from Manchester University also showed the number of mental health patients killing themselves or others was proportionately higher in Scotland.
The report found that the north-south divide was highest among teenagers.
It said alcohol and drugs were the "most pressing mental health problems in Scotland".
The Lessons for Mental Health Care in Scotland report was commissioned by the Scottish Government.
Researchers found there were 500 killings north of the border over five years and 5,000 suicides over six years.
Suicide rates in Scotland were 18.7 per 100,000 of the population, compared with 10.2 per 100,000 in England and Wales.
Of the 1,373 patient suicides in the report, there was a history of alcohol misuse in 785 cases, an average of 131 deaths per year.
There was a history of drug misuse witnessed in 522 cases, or 87 deaths per year.
About 28% of people who took their own life and 12% of killers had recently been mental health patients, the report said.
Louis Appleby, professor of psychiatry at Manchester University, said the findings suggested that alcohol and drugs lay behind Scotland's high rates of suicide and homicide.
He called the frequency with which they occurred as antecedents as "striking".
Professor Appleby added: "Alcohol and drug misuse runs through these findings and it appears to be a major contributor to risk in mental health care and broader society.
"Our findings support the view that alcohol and drugs are the most pressing mental health problems in Scotland and mental health services can play their part."
The report makes several recommendations for clinical care, including specialist community mental health teams, early follow-up after hospital discharge and improved mental health services for young people.
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