It has been suspected that herbal remedies could interact with other herbals or even prescription drugs.  Ingestion of St. John’s wort has resulted in several clinically significant interactions with drugs that are metabolized by CYP1A2 or CYP3A, including indinavir (Crixivan®){Piscitelli} and cyclosporin (Sandimmune® and Neoral®).{Breidenbach}{Ruschitzka}.   An interaction with digoxin (Lanoxin®) has also been reported that may be mediated by interference with P-glycoprotein (P-GP), a transport system that pumps drugs across membranes.{Johne}  These interactions, are most likely due to induction of the cytochrome P450 isozyme or the drug transporter, and  have caused decreased plasma concentrations of  prescription drugs.  In the case of cyclosporin, subtherapeutic levels  resulted in transplant organ rejection.

It is likely that many drug-herbal interactions exist but have not yet been detected.  It is therefore important that healthcare providers obtain a complete drug history that includes herbal remedies and other natural products and dietary supplements and that they be alert to potential interactions.

Piscitelli SC, Burstein AH, Chaitt D, Alfaro RM, Falloon J. Indinavir concentrations and St John's wort. Lancet 2000; 355(9203):547-548.
Breidenbach T, Hoffmann MW, Becker T, Schlitt H, Klempnauer J. Drug interaction of St John's wort with cyclosporin. Lancet 2000; 355(9218):1912.
Ruschitzka F, Meier PJ, Turina M, Luscher TF, Noll G. Acute heart transplant rejection due to Saint John's wort. Lancet 2000; 355(9203):548-549.
Johne A, Brockmoller J, Bauer S, Maurer A, Langheinrich M, Roots I. Pharmacokinetic interaction of digoxin with an herbal extract from St John's wort (Hypericum perforatum). Clin Pharmacol Ther 1999; 66(4):338-345.