When used appropriately and on their own, kava-kava and yohimbe offer certain health benefits. The National Institutes of Health acknowledges kava-kava's ability to ease anxiety in people with psychiatric disturbances, and yohimbe's active compound is an FDA-approved treatment for erectile dysfunction in men. Despite their therapeutic benefits, yohimbe and kava-kava should not be used together. This combination could negate the effects of both herbs and cause serious side effects, including liver failure. Consult your health care provider before using any medicinal herb.
Decreased Effectiveness
Kava-kava acts primarily as an anxiolytic, or a drug for relieving anxiety. The National Institutes of Health compares kava-kava to anti-anxiety medications including Buspar, Valium and Klonopin. As a powerful stimulant, yohimbe is likely to decrease these therapeutic effects. The NIH lists anxiety, agitation, nervousness, irritability, tremors and insomnia-- the very symptoms that kava-kava can treat-- among the most common side effects of yohimbe bark.
Intoxication
In sufficiently high doses, both yohimbe and kava-kava can be intoxicating. While no studies have evaluated the use of the two herbs in synergy, it is quite possible that they can exacerbate the effects of one another. The NIH notes that yohimbe can increase the intoxicating effect of other products, including alcohol, morphine and caffeine. When combined, kava-kava and yohimbe may trigger episodes of euphoria, disorientation and poor judgment similar to alcohol use. Although some people may use these herbs for recreational intoxication, it is important to understand the dangers associated with this practice. Refrain from driving, engaging in childcare or operating heavy machinery while using any intoxicating combination of medicinal herbs.
MAOI Activity
The National Institutes of Health reports that both kava-kava and yohimbe bark extract may be similar to monoamine oxidase inhibitors, or MAOI drugs. When combined, herbs with MAOI activity can cause life-threatening side effects. The NIH warns that yohimbe may trigger an episode of extremely high blood pressure, or hypertensive crisis, when combined with other MAOI compounds. Avoid both yohimbe and kava-kava under all circumstances if you are taking a prescription MAOI such as Marplan or Nardil.
Changes in Metabolism
The most significant concern regarding the use of kava-kava and yohimbe relates to the herbs' effects on liver enzymes. Both kava-kava and yohimbe alter the liver's cytochrome P450 enzyme system, which controls levels of drugs and other compounds in the bloodstream. This alterations to the liver may, according to the NIH, cause one or both drugs to enter the bloodstream in astronomically high amounts, leading to a dangerous overdose of both herbs. Furthermore, this effect may interfere with the absorption of prescription and over-the-counter drugs. These alterations in metabolism may have life-threatening consequences.
Liver Failure
Multiple case reports have linked kava-kava to liver damage, including fibrosis, hepatitis, cirrhosis and liver failure. Although many health care practitioners believe that kava-kava is safe when used appropriately under a physician's guidance, the NIH sternly warns against combing kava-kava with other drugs or herbs that are metabolized by the liver. Because yohimbe alters levels of liver enzymes, it can drastically elevate the risk of liver failure for people taking kava-kava. This risk is particularly serious for people with pre-existing liver diseases such as hepatitis or alcoholic cirrhosis.
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