The in vitro drug interaction potential of dietary supplements containing multiple herbal components.

Herbal-based remedies are widely used as alternative treatments for a number of ailments. In addition, the use of products that contain both single and multiple herbal constituents is becoming increasingly common. The work described in this report examined the in vitro drug interaction potential for a commonly used herbal cold remedy reported to contain a mixture of eight herbal components. Experiments conducted in human liver microsomes exhibited significant inhibition (<10% of control activity remaining) of multiple cytochrome P450 (P450) isoforms, including CYP2B6, CYP2C9, and CYP2D6, by the herbal mixture. In an attempt to explain the observed P450 inhibition by the herbal mixture, individual active components were obtained and tested for inhibitory potency. Inhibition of multiple P450 activities by a single constituent, luteolin, was observed. Conversely, inhibition of a single isoform by several herbal components was noted for CYP2B6. Based on the data presented, it is concluded that mixtures of herbal components may exhibit multiple modes of P450 inhibition, indicating the potential for complex herbal-drug interaction scenarios to occur.