Cedar leaf oil, or CLO, comes from a genus of trees known as Thuja, which includes coniferous cedar trees. The name comes from the Greek word “thuo” which means “to sacrifice.” The wood was burned as part of sacrifices to the gods. Native Americans still use its smoke to lift prayers to God. CLO contains a potent neurotoxic substance called thujone. No studies currently document safe and effective uses of cedar leaf oil, and its medical use is not recommended.

Chemical Constituents

The volatile oil produced by cedar leaves and twigs contains about 65 percent thujone, which is a hydrocarbon and a toxic chemical. Borneol, finchone, picine, camphor, limonene, tannin, myrcin and thujin are also found in CLO.

Purported Uses

Cedar leaf oil has been used for thousands of years as an herbal remedy. It has been used as an abortifacient, an emmenagogue, a diuretic and a remedy for stomach disorders. It is sometimes applied externally to relieve the pain of arthritis and is used as a vermifuge against parasites. Applied topically, cedar leaf oil has been used to treat fungus, thrush and eczema on the skin 2. It has been used against viruses and tumors. Rich in vitamin C, the leaves have been used for scurvy, and an extract has been used for treating influenza Type A. Thuja is also popular as a homeopathic preparation.

Despite CLO’s long use in herbal medicine, well designed studies on the effectiveness of this herb are all but non-existent. Cedar leaf oil is not recognized as safe and effective for any medical use and has serious side effects and toxicities.

Side Effects

Cedar leaf oil may cause contractions of the uterus, producing spontaneous abortion 2. Asthma attacks, gastrointestinal irritation, nervous system stimulation, spasms, seizures, hallucinations and damage to the liver and kidneys may occur with cedar leaf oil use 2.


Persons with allergies to cedar pollen should avoid using CLO. Exposure can cause itching, swelling, or redness of the skin. Difficulty or pain in breathing, chest tightness, and swelling of the mouth, lips, face and throat are possible with thujone allergies. Seek medical help immediately if you experience such symptoms.


Thujone is a neurotoxin found in absinthe, some furniture polishes, in CLO oil, and in some homeopathic preparations. Symptoms of thujone poisoning can include difficulty breathing, throat swelling, burning in the eyes, ears, lips, nose, throat, or lungs, esophageal burns, abdominal pain, vomiting--sometimes bloody--circulatory collapse, low blood pressure, loss of vision, seizures, stupor, coma, skin burning or irritation.

If you suspect thujone poisoning, do not induce vomiting. Seek medical help immediately. Call 911 and ask for the poison control center for further instructions.


Pregnant or nursing women should not use CLO due to the possibility of spontaneous abortion. CLO should be kept out of the reach of children and not used in this population because of its toxicity.

Persons with gastrointestinal ulcers or other conditions should avoid cedar leaf oil, as should those with seizure disorders.

Currently, there are no medically recognized uses for cedar leaf oil 2. Its use is not recommended.