Berberine is an isoquinoline alkaloid plant extract that is widely available as a dietary supplement in the United States and has demonstrated efficacy in the treatment of type 2 diabetes mellitus and dyslipidemia. Because of its increased use and purported pharmacological properties, potential variations in product quality could pose a barrier to berberine's safety and effectiveness in clinical practice. Thus, this study evaluated the potency of dietary supplements containing berberine available in the U.S. commercial market. Fifteen unique dietary supplements containing berberine were purchased through U.S. dietary supplement vendors. For each product, berberine was extracted from 3 unique capsules and analyzed by ultra-high-performance liquid chromatography tandem mass spectrometry. Percentage content based on the product label claim was determined for each product. The average berberine content across the products was found to be 75% ± 25% of the product label claim, with product potency ranging from 33% to 100%. Nine of the 15 tested products (60%) failed to meet the potency standards of 90% to 110% of labeled content claim, as commonly required of pharmaceutical preparations by the U.S. Pharmacopeial Convention. Evaluation of the relationship between product cost and the measured potency failed to demonstrate an association between quality and cost. Variability in product quality may significantly contribute to inconsistencies in the safety and effectiveness of berberine. In addition, the quality of the berberine product cannot be inferred from its cost.
Keywords: berberine; dietary supplement; natural product; potency.