Kava is as effective as anti-anxiety medications and has fewer tolerance issues. Its short term use is well established and long term seems viable despite a few rare adverse events (possible interactions). Additional herbs with anti-anxiety effects are chamomile, passionflower, lemon balm, and bacopa monnieri. Sources
"For anxiolytic activity the recommended doses are 50–70 mg kavalactones two to four times per day" (Bilia, Gallori, and Vincieri, 2002). In capsule form kava is usually standardized to a certain kavalactone percentage as seen in the first recommended product below. With kava in its natural or powder form dosing is more difficult, so it should be used with discretion and not overconsumed. Also, kava derived from the root is the safest (Teschke and Schulze, 2010).
Kava Capsules 120 caps 75mg kavalactones each
Chamomile, passionflower, lemon balm, trytophan, and more 60 caps
Kava Powder 1 lb
Passionflower 180 caps 1100mg each
Chamomile Capsules 100 caps 350mg each
Lemon Balm Capsules 200 caps 500mg each
Kava, Chamomile, Valerian, Lavender 40g Tea
Chamomile Tea 16 oz bag
*A note on Kava's rare liver hepatoxicity events: It is very rare, but there have been a few cases of toxic liver disease that may be linked to kava consumption (Stevinson, Huntley, and Ernst, 2002; Teschke, Gaus, and Loew, 2003). If you have any liver issues kava might not be a great option. Some recommend it not be used long term because of these rare events. That being said, many studies as shown above cite its safety and tolerability. Still, use with discretion.