Does Diminished Dopaminergic Neurotransmission Increase Pica?

We behaviorally evaluated the hypothesis that pica in some individuals with mental retardation may be maintained or exacerbated by the use of neuroleptics. Three older adolescents, with profound mental retardation and a history of pica, were chosen for study because they 1) had proven intractable to well-designed behavioral treatments derived through a functional analysis of their pica, 2) were already being prescribed a neuroleptic specifically for their pica, and 3) had tested negative for iron deficiency. The effects of the dopamine antagonist thioridazine on pica were evaluated in a single-subject, double-blind, placebo-controlled, drug-withdrawal design. This experimental phase was followed by a clinical phase in which the effects of the dopamine agonist methylphenidate on pica were observed. The three subjects received 2.5-4.0 mg/kg daily of thioridazine during the two active drug phases in the withdrawal design, and each received methylphenidate (0.6 mg/kg daily) during the clinical phase. When compared to the placebo phases, all subjects engaged in higher levels of pica during the thioridazine phases. The lowest levels of pica were observed in the clinical phase when the subjects were taking methylphenidate. There are a number of reasons why increased levels of pica could have been observed during thioridazine treatment. These preliminary data support the hypothesis that diminished dopaminergic neurotransmission may play a role in the maintenance and exacerbation of pica in some individuals with mental retardation, and suggest that neuroleptic treatment of pica might actually worsen the behavior. Additional research is needed before methylphenidate can be recommended as a treatment for pica.