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heart transplant patients maintained on cyclosporine therapy. Clinicians are warned that
St. John's Wort may significantly affect plasma concentrations of any drug that is
metabolized by the cytochrome P450 system.
• Warfarin: It is interesting to note that the combined use of St John’s wort and warfarin
usually causes neutralization of the effect of warfarin by increasing its metabolism via the
P450 enzyme system.
• Benzodiazepines: e.g. Alprazolam.
• Theophylline: The herb decreases theophylline levels on a patient stabilized on
theophylline therapy.
• Medications for HIV/AIDS (Nonnucleoside Reverse Transcriptase Inhibitors (NNRTIs))
• Medications for HIV/AIDS (protease inhibitors) e.g. Indinavir coadministration reduces
indinavir plasma levels.
• Ethinyloestradiol and desogestrel (combined oral contraceptive): Breakthrough bleeding
has occurred with concomitant use of St. John's Wort.
• Anticonvulsants (carbamazepine, phenobarbitone and phenytoin).
Digoxin: Co-administration of St. John's Wort extract with digoxin resulted in a significant
decrease in digoxin blood level. Therefore, St. John's Wort may reduce efficacy of digoxin and
make a patient a nonresponder, whereas increased toxicity may be anticipated after withdrawal
of the herb. The mechanism involved may be induction of the P-glycoprotein drug transporter.
Iron: Tannic acids present in St. John's Wort may inhibit the absorption of iron.
Photosensitizers, such as tetracyclines, sulfonamides, thiazides, quinolones, piroxicam and
others should be avoided.

Diagram of the T.S. of the stem

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