Currently, there is little scientific evidence to support the use of alternative therapies, such as homeopathy, herbs and acupuncture, for COPD. While a number of therapies are probably harmless, others may pose considerable risk. Homeopathy, yoga and acupuncture are probably safe. Trials of acupuncture have shown inconclusive evidence of positive effects in the treatment of respiratory disorders. Other alternative therapies, such as herbal medications, vitamin supplements and restrictive diets, pose greater risks to people. A few herbal medications, mostly from India and Southeast Asia, contain a variety of contaminants, ranging from aspirin, steroids and narcotics, to toxic substances such as lead, mercury and arsenic. The most concern is for the herbal preparation ma huang, which contains ephedra, a natural bronchodilator. This has several side effects that can lead to heart attacks, strokes and blood pressure crises. Prescribed bronchodilators, such as albuterol, have considerably fewer side effects. Licorice, a plant used not only in flavoring but also in herbal mixtures, inhibits steroid metabolism. Patients who use licorice to reduce their steroid medications are still exposing themselves to steroids and their potential systemic side effects. The amount of licorice used to flavor candy, however, poses little to no risk.