Although they've treated anxiety for centuries, plant-based remedies haven't been studied by scientists as thoroughly as manufactured drugs, and should never be used by pregnant or nursing women. The three most common are:
Kava: Widely considered the most effective natural remedy for anxiety, though the FDA has advised consumers that it might be associated with liver injury. It may also cause a scaly skin rash called kava dermopathy. Can be brewed into a liquid or taken as a powder, and doesn't cause mental impairment.
Saint John's Wort: Has been used to treat depression and anxiety since ancient Greek times. Never take Saint John's Wort if you're taking other drugs without checking with your doctor, and be careful in the sun—it makes skin more sensitive to light.
Valerian root: Traditional cure for insomnia. More suited for use as a sleeping aid than as a treatment for daytime anxiety. Smells like stinky cheese.