The eucalyptus tree originated in Australia and Tasmania, but has now been spread to all other inhabited continents. There are many different varieties of eucalyptus, with somewhat differing constituents. The most common type used medicinally is eucalyptus globules. Its essential oil contains eucalyptol (cineol or cineole).

Eucalyptus oil has long history of use as a topical antiseptic. It has also been used as a lozenge or inhalation therapy for asthma, cough, sore throat, and other respiratory conditions.

A standardized combination of cineol from eucalyptus, d-limonene from citrus fruit, and alpha-pinene from pine has been studied for effectiveness in a variety of respiratory conditions. These oils are all in a chemical family called monoterpenes, and for this reason the combined treatment is called “ essential oil monoterpenes.” This combination is discussed in a separate article of that name. Other combination therapies containing eucalyptus oil are discussed in the article titledAromatherapy.

Eucalyptus oil or its constituents taken alone have undergone only limited study. It appears to be most promising as a treatment for the common cold. However, concerns about safety have limited its use.

In a double-blind, placebo-controlled study of 152 people, use of cineol at a dose of 200 mg three times daily markedly improved symptoms of the common cold.1 Benefits were seen in such symptoms as nasal congestion, headache, and overall malaise. Because the participants in this study suffered, in particular, from sinus symptoms, this study has been used to indicate that cineol may be helpful for viral sinusitis. Few significant side effects were seen in this study, but the product used was of pharmaceutical grade, and not all dietary supplements of eucalyptus oil may be equally safe. A second placebo-controlled study involving 150 subjects also demonstrated favorable results of cineol compared to a combination of five other herbal products.6

Researchers have also studied the potential benefits of eucalyptus paired with cayenne. In a small randomized trial, a product called Sinus Buster (an intranasal spray that includes cayenne and eucalyptus) helped to improve sinus problems in people with nonallergic rhinitis.8

In another study, 32 people on steroids to control severe asthma(steroid-dependent asthma) were given either placebo or cineole (200 mg three times daily) for 12 weeks.2 The results showed that people using cineole were able to gradually reduce their steroid dosage to a greater extent than those taking placebo. NOTE: Reduction of steroid dosage should be done only under the supervision of a physician.

Cineole or eucalyptus oil applied topically has also shown some potential value for repelling mosquito bites.3

In one double-blind study, chewing gum containing eucalyptus extract was more beneficial for moderate gingivitis compared to a placebo gum.7