Kava, a plant product prepared from Piper methysticum, has been used for centuries in the South Pacific to relieve anxiety and insomnia. Also sold as a dietary supplement in the U.S., kava has recently been found through a randomized control study as an effective treatment for generalized anxiety disorder (GAD).

Indigenous to places like Fiji, Samoa, and Vanuata, the root has mild sedative and anesthetic properties, and can produce a mild euphoria and sense of relaxation. Traditional medicine specialists from the area have used kava to treat a range of disorders, from asthma, urinary tract infections, to menopausal symptoms, and have also used kava as a topical numbing agent. In the U.S., kava root is sold as an herbal supplement in tablet form, or as dried and ground root powder that can be made into a tea-like beverage.

Led by Jerome Sarris, researcher from the Department of Psychiatry in the University of Melbourne, the research team had previously established that kava was effective in treating chronic generalized anxiety in a short term study. This new research builds upon this evidence by restricting participants to a clinically-defined group with no other comorbid depression.

General anxiety disorder is characterized by constant worry that is so difficult to control that it interferes with everyday life. The disorder is marked by headaches, trouble falling asleep, and difficulty concentrating. According to the National Institute of Mental Health, 5.7 percent of Americans will experience GAD at some point in their lifetime.

Usually, GAD is treated with a combination of psychotherapy and medications. Types of prescriptions include antidepressants, such as paroxetine (Paxil) and sertraline (Zoloft), or benzodiazepines, like diazepam (Valium) or alprazolam (Xanax).

However, these medications come with potentially serious side effects and at times produce only a modest clinical effect. Nausea and insomnia were each reported by over one in five users of Paxil and Zoloft. Benzodiazepines may cause poor muscle coordination and drowsiness. Kava is hoped to be a promising alternative, because it is not as sedating or mentally impairing as some of these drugs.

Researchers recruited 75 participants ages 18-65 with a confirmed diagnosis of GAD. Over the course of 8 weeks, participants took either placebo or 120-240 mg per day of the psychoactive compounds in kava, called kavalactones. Both researchers and participants were blind to who took what.

Participants were evaluated periodically using the Hamilton Anxiety Rating Scale, a short questionnaire about symptoms and feelings related to anxiety, and measured for biomarkers of anxiety response.

At the end of the experiment, there was a significant reduction in anxiety for the kava group compared with the placebo group, and the effect was larger in those who have moderate to severe GAD. Furthermore, 26 percent of the kava group were considered relieved of their anxiety.

Overall, kava did not work for everyone, and only 37 percent of patients in the kava group and 23 percent in the placebo group responded to the intervention. Study researchers write that this modest response rate is a testament to the difficulty of treating GAD, a disorder that has been elusive to treat with pharmaceuticals.

People in the kava group reported more headaches, but the two groups had no other significant differences for adverse effects.

Researchers also measured liver function tests in both groups, and found no differences. Liver function was evaluated because the U.S. Federal Drug Administration issued a warning in 2002 about a possible association between severe liver injury and kava use. Currently, the FDA does not fund any research investigating the potential benefits of kava.

Cases of liver injury — including hepatitis, cirrhosis, and liver failure, have been rare, but serious. A handful of cases required a liver transplant. Some speculate that the risk originates from improperly prepared kava that incorporates leaves and stems.

Kavalactones, the psychoactive ingredient in kava, have been studied in vivo and in vitro. It has many suspected mechanisms of action, some of which are shared with anti-anxiety and anti-depressant medications. A suspected action mechanism is that kavalactones induce ligand binding to GABA type A receptors, the molecular target of benzodiazepines, or possibly kavalactones inhibit the reuptake of norepinephrine and dopamine, which is how some drugs for treating clinical depression work.

Sarris's work contributes to a growing body of evidence that points to kava's potential in treating anxiety. A review of 11 studies on kava as a treatment for anxiety, insomnia, and restlessness, either alone or in conjunction with other drugs, shows that seven of the studies indicated that kava had a positive effect. The remaining four found no difference between kava and placebo.

Sources: Lakhan, SE, Vieira, KF. Nutritional and herbal supplements for anxiety and anxiety-related disorders: systematic review. Nutr J. 2010

Sarris, J, Stough, C, Bousman, CA, Wahid, ZT, Murray, G, Teschke, R, Savage, KM, Dowell, A, Ng, C, Schweitzer, I. Kava in the Treatment of Generalized Anxiety Disorder: A Double-Blind, Randomized, Placebo-Controlled Study. Journal of Clinical Psychopharmacology. 2013.