For emergency room doctors, they are a dispiriting and familiar sight: Children who return again and again in the grip of mental health crises, brought in by caregivers who are frightened or overwhelmed.

Much has been written about the surge in pediatric mental health emergency visits in recent years, as rates of depression and suicidal behavior among teens surged. Patients often spend days or weeks in exam rooms waiting for a rare psychiatric bed to open up, sharply reducing hospital capacity.

But a large study published on Tuesday found a surprising trend among adolescents who repeatedly visited the hospital. The patients most likely to reappear in emergency rooms were not patients who harmed themselves, but rather those whose agitation and aggressive behavior proved too much for their caregivers to manage.

In many cases, repeat visitors had previously received sedatives or other drugs to restrain them when their behavior became disruptive.