Common reported side effects are[10][11]: difficulty sleeping (which can lead in turn to other problems); loss of appetite (thus its use as an appetite suppressant); irritability; nervousness; stomach aches; headaches; dry mouth; blurry vision; nausea; dizziness; drowsiness; motor tics or tremors. Up to 5% of children experience disturbing hallucinations often involving worms, snakes, or insects (New Scientist, 31 March 2006).
Less common side effects are: hypersensitivity; anorexia; palpitations; blood pressure and pulse changes; cardiac arrhythmia; anemia; scalp hair loss; toxic psychosis.
There have also been reports of: abnormal liver function; cerebral arteritis; leukopenia; death. There have been at least 19 cases of sudden death in children taking methylphenidate, leading to calls by the Drug Safety and Risk Management Advisory Committee to the FDA to require the most serious type of health warning on the label, but this advice was rejected (New Scientist 18 Feb. 2006).
Medline [12] lists a number of side-effects of unquantified frequency.