After six months, the numbers were 49 percent and 32.6 percent respectively.

The researchers also found a greater incidence of nausea, disturbed sleep, skin reactions and depression in the combination group. They say safety and long-term efficacy needs to be assessed by further studies.

Don't pressure your doctor after a concussion

Journal: Neurology

After a concussion, doctors often receive pressure from their young patients, families and coaches to give an athlete the "all-clear" as soon as possible.

But that's dangerous, says the American Academy of Neurology. The reason: Concussions are linked to long-term impairments in brain function. A new position statement published in the journal Neurology on Wednesday calls for doctors to only give an athlete the "all-clear" to play when medically ready.

"Physicians should be thoughtful about athletes going back to field after brain injury," says neurologist Dr. Daniel Larriviere, one of the study authors.

Doctors caring for athletes with sports-related concussions should have adequate training and experience and also educate patients and their families about the dangers of concussion, the authors conclude. The academy is also calling for a national registry the will require mandatory reporting of concussions.