What are the Side Effects of the Wormwood Herb

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Wormwood leaves on a cutting board.
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Wormwood, native to Europe and naturalized to the northeastern North American continent, has a long and checkered history as an herbal remedy. Traditional Western herbalists prescribed wormwood, officially known as Artemisia absinthium, to treat liver and kidney disease, counteract poison, kill intestinal parasites and cure drunkenness. Botanist James Duke notes that the last use is ironic, considering that wormwood is one of the main ingredients in absinthe, an alcoholic beverage believed to be so addictive and so damaging that many governments banned its sale in the early 1900s.

Muscular Contractions

A component of wormwood, thujone, causes muscular contractions and spasms, including uterine contractions. Pregnant and breastfeeding women should avoid its use for that reason, according to the American Cancer Society's website. Wormwood may also cause breakdown of muscle tissue.

Nerve Damage

Thujone also may be toxic to nerves. People who overuse wormwood or take wormwood essential oil--which contains higher levels of thujone than wormwood tea or tincture--may have seizures or convulsions, or experience hallucinations. Some experts disagree that wormwood causes these symptoms and side effects. In one German study, for instance, researchers gave 20 patients suffering from Crohn's disease an herbal preparation that contained wormwood. The study reported no serious side effects from the use of wormwood, according to a short article at the Tufts Medical Center website. Studies like this one and others that have shown a relatively low concentration of thujone in wormwood preparations have led some herbalists to question the traditional belief that wormwood is highly toxic except in very high doses.

Kidney Failure

Ingesting wormwood essential oil may cause kidney failure, according to a case study published in the New England Journal of Medicine. The report concerns a man who drank oil of wormwood, thinking it was absinthe. His symptoms included convulsions, muscle breakdown, congestive heart failure and acute kidney failure.

Other Side Effects

High doses of wormwood herbal preparations may also cause nausea, vomiting, stomach cramps, headaches, dizziness, nervous system problems and seizures, according to the American Cancer Society website.

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