Without the risk of serious side effects, herbal supplements containing extracts of passionflower or kava and combinations of [amino acids] L-lysine and L-arginine are treatments for anxiety symptoms and disorders.
Magnesium-containing supplements is also worth a try.
St. John’s wort monotherapy has insufficient evidence for use as an effective anxiolytic treatment.
Source: Nutrition Journal, Oct 7, 2010;9:42. PMID: 20929532, by Lakhan SE, Vieira KF. Global Neuroscience Initiative Foundation, Los Angeles, California, USA.