Oregon grape (Mahonia aquifolium) has a history of both traditional and scientific use for supporting the health of mucus membranes, particularly of the gastrointestinal tract and skin. Traditionally, Native American and Western herbal medicine systems have used Oregon grape root as a remedy for various ailments, including digestive disturbances and skin conditions, which often involve the mucus membranes.

From a scientific perspective, Oregon grape contains several active alkaloids, most notably berberine. Berberine has demonstrated antimicrobial, anti-inflammatory, and immunomodulatory properties in in vitro and animal studies. These properties can help protect and support the integrity of mucus membranes by reducing inflammation and inhibiting the growth of harmful microbes. Specifically, berberine has been shown to inhibit the adhesion and invasion of pathogenic bacteria in the gut, and it may help restore the balance of healthy gut flora, which is essential for the proper function of the gastrointestinal mucus membrane.

Small clinical studies have evaluated Oregon grape extract for conditions like psoriasis (a skin disorder with mucus membrane involvement), showing some benefit, although larger, well-controlled human trials are lacking. Overall, while the traditional use is strong and there is a moderate level of scientific support, especially for the alkaloid berberine, the evidence is not robust enough for a higher rating.