Effect of L-tryptophan on memory in patients with schizophrenia

It has been well established that patients with schizophrenia have impaired cognitive abilities on neuropsychological tasks related to memory. Previous studies also suggest a central role for serotonin in memory. This double-blind crossover study aimed to explore the effect of L-tryptophan, a serotonin precursor, on a variety of memory tasks in schizophrenic patients. Antipsychotic-treated schizophrenic patients in remission (N = 21) were randomly treated with L-tryptophan or placebo and then evaluated at three consecutive points on clinical measures (including Positive and Negative Syndrome Scale for Schizophrenia, Clinical Global Impression, and Extrapyramidal Symptoms Rating Scale) and by neuropsychological tests (including Digit-Span, Paired Association, Rey-Osterich Complex Figure Test, Digit Symbol, Number Facility Test, and the Rivermead Behavioral Memory Tests. Compared with placebo, L-tryptophan had a beneficial effect on memory functions but not on the patients' psychotic state or on the side effects of medications. These preliminary results suggest the possibility of using serotonin precursor to enhance memory function in schizophrenia.