High doses of antidepressants may increase the risk of self-harm in children and young adults, according to a recent study.

Researchers from the Harvard School of Public Health in Boston found that children and young adults who start antidepressant therapy at high doses, rather than the average or typical prescribed doses, appear to be at greater risk for suicidal behavior during the first 90 days of treatment.

"Our findings offer clinicians an additional incentive to avoid initiating pharmacotherapy at high-therapeutic doses and to monitor all patients starting antidepressants, especially youth, for several months and regardless of history of [deliberate self-harm]," researchers said.

For the study, researchers analyzed data from 162,625 people - between the ages of 10 and 64 years - with depression who started antidepressant treatment with a selective serotonin reuptake inhibitor at modal (the most prescribed doses on average) or at higher than modal doses from 1998 through 2010.

They found that the rate of suicidal behavior among those 24 years and younger started antidepressant therapy at high doses was about twice as high compared with a matched group of patients who received generally prescribed doses.

Researchers said they believe this corresponds to about one additional event of deliberate self-harm for every 150 patients treated with high-dose therapy. For adults 25 to 64 years old, the difference in risk for suicidal behavior was null.

A previous meta-analysis by the U.S. Food and Drug Administration of antidepressant trials suggested that children who received antidepressants had twice the rate of suicidal ideation and behavior than children who were given a placebo.

The current study sought to examine suicidal behavior and antidepressant dose, and whether risk depended on a patient's age.

The study does not address why higher doses might lead to higher suicide risk.

The findings were recently published in The JAMA Network Journals.