The roots and bark of the shrub Mahonia aquifolium (also called Oregon grape) have traditionally been used both orally and topically to treat skin problems. They were also used for other conditions such as gastritis, fever, hemorrhage, jaundice, gall bladder disease, and cancer. In addition, Mahonia was used as a bitter tonic to improve appetite.

According to some experts, M. aquifolium is identical to the plant named Berberis aquifolium, but others point to small distinctions. Berberis vulgaris, commonly called barberry, is a close relative of these herbs, but is not identical.

What Is Oregon Grape Used for Today?

Oregon grape is primarily used today as a topical treatment for psoriasis. Growing evidence suggests that it may help reduce symptoms, although it does not seem to be as effective for this purpose as standard medications.1,2,3,15

Oregon grape has been proposed as a treatment for other skin diseases, such as fungal infections (such as athlete's foot), eczema, and acne.4,5,6 However, the evidence is either extremely preliminary or inconclusive. For example, a double-blind, placebo-controlled study of 88 people with eczema tested a cream containing extracts of Mahonia aquifolium, Viola tricolor, and Centella asiatica.17 The results failed to show benefit overall.

Many studies have been performed on purified berberine, a major chemical constituent of Oregon grape and other herbs such as goldenseal, but it is not clear whether their results apply to the whole herb. In addition, impossibly high dosages of the herb would be required to duplicate the amount of berberine used in many of these studies. (For more information, see the article on Goldenseal.)

What Is the Scientific Evidence for Oregon Grape?

Evidence from two double-blind, placebo-controlled studies and one comparative trial suggest that cream made from the herb Oregon grape may help reduce symptoms of psoriasis, although it does not seem to be as effective as standard medications.

In a double-blind study published in 2006, two hundred people were given either a cream containing 10% Oregon grape extract or placebo twice a day for 3 months.15 The results indicate that the people using Oregon grape experienced greater benefits than those in the placebo group, and the difference was statistically significant. The treatment was well tolerated, though in a few people it caused rash or burning sensation.

Benefits were also seen in a double-blind, placebo-controlled study of 82 people with psoriasis.7 However, the study design had a significant flaw: the treatment salve was darker in color than the placebo, possibly allowing participants to guess which was which.

Another study found that dithranol, a conventional drug used to treat psoriasis symptoms, was more effective than Oregon grape.8 Regrettably, the authors fail to state whether this study was double-blind. Forty-nine participants applied one treatment to their left side and the other to their right for 4 weeks. Skin biopsies were then analyzed and compared with samples taken at the beginning of the study. The physicians evaluating changes in skin tissue were unaware which treatments had been used on the samples. Greater improvements were seen in the dithranol group.

A large open study in which 443 participants with psoriasis used Oregon grape topically for 12 weeks found the herb to be helpful for 73.7% of the group.9 Without a placebo group, it’s not possible to know whether Oregon grape was truly responsible for the improvement seen, but the trial does help to establish the herb's safety and tolerability. (See Safety Issues below.)

Laboratory research suggests Oregon grape has some effects at the cellular level that might be helpful in psoriasis, such as slowing the rate of abnormal cell growth and reducing inflammation.10,11

Dosage

Topical ointments or creams containing 10% Oregon grape extract are generally applied 3 times daily to the affected areas.

Safety Issues

Oregon grape appears to be safe when used as directed. In the large open study described above, only 5 of the 443 participants reported side effects of burning, redness, and itching.12

However, because Oregon grape contains berberine, which has been reported to cause uterine contractions and to increase levels of bilirubin, oral consumption of Oregon grape should be avoided by pregnant women.13,14 Safety in young children, nursing women, or people with severe liver or kidney disease has not been established.

There is an additional concern regarding the berberine content of Oregon grape. One study found that berberine impairs metabolism of the drug cyclosporine, thereby raising its levels.16 This could potentially cause toxicity.