Reviewed: Sarris J, Laporte E, Scholey A, et al. Does a medicinal dose of kava impair driving? A randomized, placebo-controlled, double-blind study. Traffic Inj Prev. 2013;14(1):13-17.

It is well known that alcohol and certain pharmaceutical and recreational drugs can impair driving and increase the risk of accidents. Some medical researchers have expressed concerns that kava (Piper methysticum, Piperaceae) root and its preparations have the potential to cause inebriation similar to that caused by psychotropic substances such as alcohol and benzodiazepines (a class of pharmaceutical anti-anxiety drugs, which includes the well-known drug Valium^®). Therefore, it is possible that kava may impair the motor skills and cognitive abilities required for safe driving. For this reason, the German Commission E, in its therapeutic monograph on kava published in 1990, included a precaution with respect to driving an automobile or operating heaving machinery while under the influence of kava.^1*

The purpose of this three-arm, randomized, placebo-controlled, double-blind, crossover trial was to evaluate the acute effects of kava on driving performance. This study was part of the Kava Anxiety-Lowering Medication (KALM) Project, conducted by the Brain and Psychological Sciences Research Centre at Swinburne University of Technology in Melbourne, Australia. Men and women (n=22; aged 16-65 years) with mild-to-moderate anxiety were recruited via advertising media distributed in Hawthorn, Victoria, Australia. Patients were excluded for the following criteria: current use of antidepressants, mood stabilizers, antipsychotics, opioids, analgesics, or cannabis; substance abuse or dependency disorder in the previous six months, including alcohol abuse/dependency; previous adverse reaction to kava or benzodiazepines; regular use of kava or benzodiazepines in the previous 12 months; more than one occasion of benzodiazepine or kava use each week over the past month; pregnancy, trying to conceive, or those who could be pregnant; regular smokers (more than one cigarette a week); and those with abnormal liver function.

Participants were subjected to a 10-minute practice session on a driving simulator. They then received either three kava tablets containing a combined total of 180 mg of kavalactones, 30 mg of oxazepam (a benzodiazepine), or placebo. All treatments looked identical. The kava tablets (MediHerb Kava, Integria Healthcare Pty Ltd; Warwick, Australia) were standardized to contain 60 mg of kavalactones per tablet. The kava preparation was manufactured using a water-extracted precipitate of the peeled rootstock from a Vanuatu noble cultivar. An independent assay using high-performance liquid chromatographic analysis revealed higher concentrations of the kavalactones dihydrokawain, kawain, and dihydromethysticin; moderate levels of methysticin and yangonin; and lower levels of desmethoxyyangonin. The alkaloid pipermethystine was not present.

Following treatment administration, the patients relaxed for 90 minutes until their blood serum had appropriate levels of kava constituent. They then began a 15-minute computerized driving simulator program, followed by a visual analog assessment. One week later, patients were crossed over to another treatment. This routine was repeated a total of three times, once for each treatment.

Oxazepam produced a significantly slower braking reaction time than placebo (P=0.002) and kava (P=0.003). Concentration lapses were significantly fewer with kava than with oxazepam (P=0.033). An equal number of participants in each treatment group crashed. Results were not modified by the covariates of driving experience, driving status, or treatment order. Oxazepam-treated patients reported that they were significantly less alert than when exposed to the other treatments. All patients were more fatigued after driving, irrespective of the treatment.

According to the authors, this is the first study to evaluate the acute effects of a medicinal dose of kava on driving performance and safety compared to a benzodiazepine. The authors concluded that at medicinal doses, kava does not alter driving in the same way as benzodiazepines. Apart from its small sample size, this study had several limitations. Blood levels of oxazepam peak at two-to-three hours, and the driving analysis occurred after 90 minutes; therefore, oxazepam may have produced a more profound effect if evaluated later. The patients were not screened for medical conditions that could have altered driving vigilance, and the simulator did not exactly mimic real driving conditions. Also, the participants had mild-to-moderate anxiety, so the data may not be extrapolated to the general population.

This study gives important insight into the effects of a medicinal dose of kava on a population that would use it (i.e., patients with anxiety). However, when people use kava for recreational purposes, they consume much higher doses. Similar to alcohol, as the dose of kava increases, the ability to safely operate a vehicle may diminish. This study should be replicated with a recreational dose of kava.

—Heather S. Oliff, PhD

* The German Commission E monograph notes under Duration of Administration: “Even when administered within its prescribed dosages, this herb may adversely affect motor reflexes and judgment for driving and/or operating heavy machinery.”

Reference

1.        Blumenthal M, Busse WR, Goldberg A, Gruenwald J, Hall T, et al. The Complete German Commission E Monogaphs: Therapeutic Guide to Herbal Medicines. Austin, Texas: American Botanical Council; Boston, MA: Integrative Medicine Communications, 1998.