Reye syndrome is a rare disorder that occurs almost exclusively in children under the age of 15 and can cause severe liver and brain damage. Taking aspirin seems to significantly increase the risk of developing Reye syndrome, so do not give aspirin to anyone younger than age 20 unless told to do so by a doctor.

Reye syndrome can occur when a child seems to be recovering from a viral infection such as a cold, flu, or chickenpox. Symptoms include vomiting, lack of energy, excessive sleepiness, memory loss, confusion, and coma.