Evidence suggests that HT1001™, a proprietary North American ginseng extract containing known levels of active ginsenosides, may improve cognitive function. Importantly, individuals with schizophrenia show marked deficits in working memory, which are believed to be predictive of functional outcome in this population. The present study aimed to characterize the effect of HT1001 on working memory in a group of stable individuals with schizophrenia. In a double-blind, placebo-controlled study design, a total of 64 individuals satisfying DSM-IV criteria for schizophrenia were randomly assigned to receive either HT100 or placebo for 4 weeks. Verbal working memory and visual working memory were assessed at baseline and again at the end of the treatment phase using the Letter-Number Span Test and Visual Pattern Test, respectively. Symptoms and medication side effects were also measured at baseline and post-treatment. Visual working memory was significantly improved in the HT1001 group, but not in the placebo group. Furthermore, extrapyramidal symptoms were significantly reduced after 4 weeks treatment with HT1001, whereas no difference in extrapyramidal effects was observed in the placebo group. These results provide a solid foundation for the further investigation of HT1001 as an adjunct therapy in schizophrenia, as an improvement in working memory and a reduction in medication-related side effects has considerable potential to improve functional outcome in this population. Copyright © 2011 John Wiley & Sons, Ltd.