Controlled clinical studies are needed to clarify and determine the clinical importance of drug-herb interactions. However, it is unlikely that this information will be forthcoming except as anecdotal reports. Patients taking drugs with a narrow therapeutic index (cyclosporine, digoxin, hypoglycemic agents, lithium, phenytoin, procainamide, theophylline, tricyclic antidepressants, and warfarin) should be discouraged from using herbal products. All drugs with a narrow therapeutic index may either have increased adverse effects or be less effective when used in conjunction with herbal products. More research is required to define the interactions. When adverse reactions are experienced with drug therapy, patients must always be queried as to their intake of herbal products: what they are taking in pills and tincture form, what they are drinking as teas, and what they are eating from their garden.