Most adolescents who plan or attempt suicide have already received at least some mental health treatment, raising questions about the effectiveness of current approaches to helping troubled youths, according to the largest in-depth analysis to date of suicidal behaviors in American teenagers.

The study, in the journal JAMA Psychiatry, found that 55 percent of suicidal teenagers had received some therapy before they thought about suicide, planned it or tried to kill themselves, contradicting the widely held belief that suicide is due in part to a lack of access to treatment.

The findings, based on interviews with a nationwide sample of more than 6,000 teenagers and at least one parent of each, linked suicidal behavior to complex combinations of mood disorders like depression and behavior problems like attention-deficit and eating disorders, as well as alcohol and drug abuse.

The study found that about one in eight teenagers had persistent suicidal thoughts at some point, and that about a third of those who had suicidal thoughts had made an attempt, usually within a year of having the idea.