Ritalin is used for treating attention deficit hyperactivity disorder (ADHD) in children and adults.When you have ADHD so conquer your doctor and buy Ritalin 20mg online for your best relief. You should divide your medicine into two or three doses, and should take 30 - 45 minutes before meals.If you want to sleep well then you have to take it before 6-6:30pm.when you missed a dose so please don't take double dose at once. These are the symptoms of overdose; nausea, vomiting, diarrhea, shallow breathing, anxiety, headache and fever. When you see and feel changes or symptoms so concern your doctor.