Topic overview

Start with the big picture

Herbal–drug interactions may be pharmacokinetic, such as altered CYP enzyme or P-glycoprotein activity, absorption, or renal handling, or pharmacodynamic, through additive, opposing, or overlapping effects. Examples include St John’s wort reducing levels of some medicines, grapefruit juice increasing exposure to selected drugs, and sedative herbs adding to central nervous system depression. Other concerns include bleeding risk, altered INR, electrolyte effects, and reduced absorption from tannin- or fiber-rich products. Risk is greater with polypharmacy and narrow-therapeutic-index medicines, among other factors. The deeper lesson also addresses pharmacovigilance, causality assessment, clinical management, and strategies for reducing risk.