Objective To investigate if adjunctive artemisinin, an anti-malarial compound with in vivo activity against Toxoplasma gondii, reduces symptoms or antibodies in schizophrenia. Method N=66 outpatients with schizophrenia were randomized to receive 100mg of artemisinin twice a day or placebo for 10weeks after a 2week placebo run-in in addition to their usual psychiatric medications. Symptoms were assessed biweekly. Antibodies to toxoplasma and to gliadin, a food antigen, were assessed at the beginning and end of the trial. Results A total of 57 participants (26 in the artemisinin arm and 31 in the placebo arm) completed the 12weeks of the trial. The medication was well tolerated and there were no significant side effects associated with the treatment regimen. There was no significant difference in the change of positive, negative, general, or total PANSS symptoms between groups for all of the randomized patients or for just the completers. However, individuals in the artemisinin arm but not in the placebo arm had significant decreases in the levels of antibodies to gliadin (p<.0005, p>.2, respectively by paired t-test). Neither group had significant changes in antibodies to T. gondii. Conclusions The study did not demonstrate clinical benefit of adjunctive artemisinin for schizophrenia symptoms. The finding of reduced levels of antibodies to gliadin in the artemisinin group merits further study.