Thuja occidentalis side effects

Updated April 17, 2017

The dried twig tips of Thuja occidentalis, known as the Eastern arbor vitae or Northern white cedar, are used in folk medicine and homeopathy to treat a variety of viral respiratory ailments, including the common cold, as well as scurvy, psoriasis and rheumatism. But, high doses of the plant or its extracts can be poisonous and can induce vomiting, stomach ache, diarrhoea, headache, nervousness and convulsions.

The herbal medicinal product Esberitox contains Thuja in combination with other plants thought to have medicinal value. Tinctures and pills containing Thuja are also available under such brands as LA Naturals, Boiron, Boerick and Tafel.

Risks of Internal Consumption

Take special care if you decide to treat yourself with the Thuja plant, or with an essential oil taken from the plant. Ingesting the leaves or twigs of the plant directly may lead to intoxication, and the content of its essential oil may vary widely depending on method of extraction.

The web site of the American Cancer Society warns that the "essential oil causes spasms if taken internally, and in high doses it can cause seizures as well as damage to the liver and the kidneys. The fresh leaves and shoots can also cause poisoning. Deaths have been reported. Skin or eye contact with cedar leaf oil can cause severe irritation or burns. Asthma and rashes have occurred in people who work with the wood of this tree."

The American Cancer Society also warns about thujone, a component of Thuja, which it says is known to cause muscle spasms, seizures and hallucinations if taken internally. In high doses, Thujone is known to damage the liver and the kidneys. The American Cancer Society warns against medicinal use until further study has been done.


Symptoms of intoxication by Thuja in plant form may cause vomiting, stomach ache, diarrhoea and gastroenteritis followed by absorption disorders, headache, nervous agitation and chronic convulsions and symptoms of liver and renal toxicity extending to yellow liver atrophy, arrhythmia and myocardial bleeding, according to a study published in the Oxford Journal of Evidence-Based Complementary and Alternative Medicine.

In cases of overdose and abuse, the study noted, "the oral intake of Thuja extracts induced severe metabolic disturbances. Intoxication was accompanied by an irritant effect on the gastrointestinal tract, uterus, liver and kidney. Infants who ingested leaves and twigs of fresh plant showed mild gastrointestinal disorders and vomiting."

While the study's authors considered those reactions relatively mild, they called for further study of the plant.


Patients who followed dosage recommendations for Esberitox and consumed no more than 18 to 36 milligrams of Thuja daily over one to two weeks reported few side effects, according to the study cited in the Oxford Journal.

Over a five-year period with approximately 12.2 million treated patients, patients reported 63 adverse reactions, typically having to do with organ systems, skin and appendage disorders, such as skin rashes.

It is not known, however, if those reactions were caused by Thuja itself or by the plant's reaction with other herbs in the medicine.

Pregnant Women and Children

Pregnant women, or women who are breastfeeding, should consult a doctor before using Thuja. Side effects may be more pronounced in children or babies; consult a doctor before dosing them with Thuja.

What to Do if You've Overdosed

Call 911 or a poison control centre if you detect an irregular heartbeat or find yourself vomiting or in gastrointestinal distress after consuming Thuja.

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About the Author

Nicholas Spangler, who spent eight years as a staff writer for The Miami Herald, began writing for a living in 2000. He is now a freelance writer based in Brooklyn, New York. He hold a Master of Science in Journalism from Columbia University's Graduate School of Journalism.