What happened after the federal government warned a decade ago that antidepressants might raise the risk of suicidal thoughts among young people? Instead of declining as hoped, suicide attempts over the next six years showed a small but meaningful uptick among people ages 10 to 29, according to a study published Wednesday in the journal BMJ. That increase followed a substantial drop in the use of antidepressants. Christine Y. Lu, instructor in population medicine at Harvard Pilgrim Health Care Institute, is the lead author of the study. Steven B. Soumerai, professor of population medicine, is a coauthor. Joseph Gold, assistant professor of psychiatry at McLean Hospital, is also quoted.