The Effect of a Single Dose of Kava on the EMG Activity of the Masseter Muscle: A Double-blind Crossover Pilot Clinical Study

Objective: To find out if kava, an herbal compound known to induce relaxation and promote sleep, has an effect on the EMG activity of the masseter muscle of known bruxers. Method: 24 subjects, who self reported bruxism, were included in the study. Excluded were subjects < 18 years of age, with liver problems, taking any psychoactive drugs or other herbal compounds and who were pregnant or nursing. Each subject was administered in a random manner either a capsule containing 400 mg of Kava or a capsule containing placebo. Surface electrodes were placed on the masseter muscle and connected to a portable EMG recording instrument (AT33 – Autogenic Systems). The sampling rate was 4 Hz and the measurement consisted of the average EMG activity for one minute. EMG activity was recorded at times 1, 2, 3, 4, 5, 31, 32, 33, 34, 35, 60, 61, 62, 63, 64, and 65 minutes. The procedure was repeated using the second drug at least one week later. Results: A two-tailed paired-t test showed no difference between the mean (SD) EMG activity while taking the drug 1.865 uV ± 1.618 and while taking the placebo 2.601 uV ± 3.950, t = 0.367, p > 0.30. A mixed effects crossover analysis showed no evidence for an effect for sequence, period or carryover. No adverse effects were reported. Conclusion: A single dose of 400 mg of Kava did not significantly decrease the EMG activity of the masseter muscle of known bruxers. Full-scale clinical studies are needed using an adequate sample size, a longer recording epoch and multiple doses.