Levodopa dependence and abuse in Parkinson's disease.

Two patients with Parkinson's disease repeatedly increased their levodopa dosage on their own to 1500-2000 mg/day to reach and sustain a state of euphoria, regardless of the fact that dosages of 400-800 mg/day were sufficient to suppress their parkinsonian symptoms. Both were markedly unwilling to consent to recommendations of dosage reductions, and they readily accepted adverse effects such as hyperkinesias, anorexia, and hallucinations to achieve the positive mental effects. Thus, both patients fulfilled the diagnostic criteria for substance dependence.