Methylphenidate induction of complex visual hallucinations.

A 15-year-old boy with attention-deficit hyperactivity disorder (ADHD) presented with complex visual hallucinations of rats running around and touching and smelling him soon after receiving a first low dose of methylphenidate. The hallucinations resolved upon discontinuation of the drug. Reintroduction of the drug 7 years later at an even lower dose had the same effect. Other cases of vivid complex hallucinations of living creatures associated with methylphenidate have been reported in the literature. The pathogenetic mechanism is still unknown. In our case, the occurrence of hallucinations after a very low dose of the drug on 2 occasions may suggest an idiosyncratic reaction. The phenomenon might also be explained by a drug-induced dysfunction of the monoamine transmitters. Given the wide use of methylphenidate, clinicians should be aware of this possible side effect.