A third of people who commit suicide in the United States would test positive for alcohol, while many are on drugs, a study suggests.

Researchers at the U.S. Centers for Disease Control released the conclusions Thursday after studying test results from suicide victims in 13 states.

Of those tested, 33.3 per cent were positive for alcohol and 16.4 per cent had opiates, according to the team from the CDC's National Center for Injury Prevention and Control.

Victims also tested positive for cocaine (9.4 per cent), marijuana (7.7 per cent) and amphetamines (3.9 per cent).

"These results underscore the need to continue monitoring toxicology test results of suicide victims, which might identify patterns of substance use that can help guide development of effective suicide interventions," the study's authors wrote in the CDC's Morbidity and Mortality Weekly Report.

The tests indicated the presence or absence of alcohol and other drugs, but no evaluations were done to determine whether the levels were lethal or intoxicating, the researchers said.

"In 2003, an estimated 31,484 suicides (10.7 per 100,000 population) occurred in the United States," the report said.

"Suicide was the fourth leading cause of death among persons aged 10 to 64 years and the second and third leading causes of death among persons aged 25 to 34 and 10 to 24 years, respectively."

To better understand the findings, the CDC is funding a survey of laboratories to examine testing of suicide victims.