By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) – The numbers are startling when it comes to concussions in teenagers – that is, if a Canadian study of over 2900 teens is to be believed.

The study is one where teenagers self-reported concussions and, according to their reports, 20% of them said they had traumatic brain injury.

In the survey a traumatic brain injury was defined as a head injury in which the student was unconscious for at least 5 minutes or hospitalized overnight. Twenty percent said they had traumatic brain injury in the past, 5.6% of them in the past year.

Sports injuries accounted for more than half of those recent cases, and were more common in boys.

Not all incidents were related to sports, teenagers who reported drinking alcohol and smoking marijuana in the past year had higher odds of a traumatic brain injury in the past year than those who did not.

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