St. John's Wort Changes Effects of Medication For several years now, various forms of St. John's Wort have enjoyed increasing popularity as a remedy for depressive disorders. Many persons affected by depression buy the formulas themselves, as they are available prescription-free in pharmacies and drugstores. For example, taking St. John's Wort extract lowers the concentration of Digoxin in a patient's blood by one-quarter.
Digoxin is a highly effective substance used in many cardiac stimulants.
Patients on such medication would thus have to increase their dosage when taking St. John's Wort concurrently. The effects of certain anti-depressants may also be reduced by up to 40 percent. The researchers have suggested that perhaps St. John's Wort should be available by prescription only, as individual patients cannot be expected to adjust the dosage of their medication to their St. John's Wort intake, on their own.