Berberine is an isoquinoline alkaloid found in a number of medicinal plants. Berberine-containing herbs have a long history of use in Chinese (Coptis chinensis), Western (Berberis vulgaris, Hydrastis canadensis, Berberis aquifolium), and Ayurvedic herbal medicine (Berberis aristata).
Much scientific research has been carried out on berberine, which has been shown to be an effective anti-microbial agent against many intestinal pathogens such as Giardia lamblia and Entamoeba histolytica.
Berberine salts and extracts have demonstrated in vitro inhibitory activity against Giardia trophozoites, and berberine sulfate has been shown to induce morphological damage to trophozoites, including the appearance of irregularly-shaped vacuoles, swollen trophozoites, and the development of glycogen deposits.
In a placebo-controlled clinical trial, 40 subjects received either a vitamin B-complex syrup (as a placebo), berberine hydrochloride (5 mg/kg/day), or metronidazole for six days. Berberine administration resulted in a marked decline in gastrointestinal symptoms (superior to that of metronidazole) and a 68% reduction in Giardia-positive stools. Metronidazole-treated patients were 100% parasite free, and patients on placebo had a 25% reduction in Giardia-positive stools. The authors speculated that an increase in the dose or a longer duration of treatment would increase berberine's treatment efficacy.
In an uncontrolled trial of 137 children ranging from five months to 14 years, berberine was administered in one of four regimens. Group 1 received 5 mg/kg/day for five days, group 2 received 5 mg/kg/day for 10 days, group 3 received 10 mg/kg/day for five days, and group 4 received 10 mg/kg/day for 10 days. The number of individuals with Giardia-negative stool samples was 47% in group 1, 55% in group 2, 68% in group 3, and 90% in group 4. The cure rate in group 4 was comparable to that obtained with furazolidone (92%) and metronidazole (95%). A small number of subjects in group 4 and in the metronidazole-treated group experienced a relapse one month after treatment ceased. The authors suggested either re-infection occurred or that a longer duration of treatment or multiple treatment periods may be necessary to improve overall outcomes in some patients.