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The root of kava (Piper
methysticum) has a long history of medicinal and recreational use due to
its anxiolytic effects, which previously led some in the scientific community
to question whether kava preparations cause inebriation that could impair
driving. For example, The German Commission E kava monograph, published in
1990, states on theoretical grounds, “Even when
administered within its prescribed dosages, this herb may adversely affect
motor reflexes and judgment for driving and/or operating heavy machinery.”1
In early 2013, the journal Traffic Injury
Prevention published the results of a three-arm, randomized,
placebo-controlled, double-blind trial intended to determine how a medicinal
dose of kava affected the cognition and motor skills necessary for safe
operation of a motor vehicle compared to benzodiazepines, a group of
pharmaceutical drugs typically used to treat anxiety that includes Valium®
and Xanax®.2
Twenty-two subjects of both sexes between the ages of 18 and 65 participated in
the trial, which was conducted by the Brain and Psychological Sciences Research
Centre at the Swinburne University of Technology in Melbourne, Australia, as
part of the Kava Anxiety-Lowering Medication (KALM) Project. The patients suffered
from mild-to-moderate anxiety, but were not using conventional antidepressants,
antipsychotics, mood stabilizers, analgesics, opioids, or cannabis at the time
of the trial. Tobacco smokers, individuals with a history of substance
abuse/dependency, and those who had an adverse reaction to kava or
benzodiazepines or who regularly used either substance in the preceding year were
ineligible for participation in the trial. People with abnormal liver function
and pregnant or possibly pregnant women (as well as those trying to conceive)
also were excluded.
The kava preparation utilized in the study was MediHerb® Kava
(Integria Healthcare; Warwick, Australia), which contains 60 mg of kavalactones
per tablet and is manufactured as a water-extracted precipitate from Vanuatu
noble cultivar peeled rootstock. High-performance liquid chromatography did not
reveal the presence of pipermethystine — a kava alkaloid associated with
hepatotoxicity — in the preparation.
All participants underwent a driving simulator practice session that lasted for
10 minutes. Then they were divided into three groups that were administered 180
mg kava, 30 mg of the benzodiazepine oxazepam, or placebo, after which they
were instructed to relax for an hour-and-a-half. At that point, the patients
participated in a 15-minute driving simulation and visual analog assessment.
Once a week for the two weeks that followed, each patient repeated the
procedure in a different “arm” of the trial — meaning that by the end of three
weeks, each of them had performed the simulation and testing on separate doses
of kava, oxazepam, or placebo. On oxazepam, the participants exhibited slower
braking time and more instances of lapsed concentration, although crashes
occurred with the same frequency in all treatment groups.
“The shortcomings of the trial are that it is a medicinal dose and not
the recreational dose employed by some individuals and should not be
extrapolated to this,” said Reg Lehmann, PhD, adjunct associate professor
of biological and chemical sciences at University of Queensland and Manufacturing Technical
Services Manager at Integria, who was not involved in the study (email, August
15, 2013). “The strengths of the study are
also its weakness,” Dr. Lehmann added, “in that the challenges were repetitive
rather than the totally unexpected [challenges] that you sometimes experience
on the roadways.”
“I think that [this trial] is very significant in that it was a very well-designed
double-blind crossover study in a clinical population (anxiety) using
appropriate doses of two medicines used to treat the condition,” said Ethan
Russo, MD, a neurologist and GW Pharmaceuticals Group Senior Medical Advisor
(email, August 15, 2013).
“The population was appropriate,” he continued. “Higher doses could be tested,
but that might represent a recreational use of kava vs. therapeutic. At some
dose[s], a negative effect could be observed, but this study demonstrates that
conventional doses appear to be quite safe, and more safe than a ‘conventional’
pharmaceutical.”
As to what the next logical step in this vein of kava research should be, Dr.
Russo said a similar trial “could be done in actual vehicles with a blinded
driving instructor, but this really may not contribute too much and would be
more subjective than the simulator employed in this study.”
“A larger study using a more varied driving simulation,” said Dr. Lehmann, “would
give more robust data than is found in this small 22 patient study under one
challenge situation.”
—Ash Lindstrom
References
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.
2. 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.
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