A systematic review of research into the use of nutritional supplements for the treatment of anxiety disorders has found strong evidence for the use of extracts of passionflower or kava and combinations of L-lysine and L-arginine. Researchers writing in BioMed Central's open access Nutrition Journal pooled the results of 24 studies involving a total of more than 2000 participants, showing that some nutritional and herbal supplements can be effective, without the risk of serious side effects.