Consult your physician before taking St. John's wort with conventional antidepressant drugs. Those taking MAO inhibitors should avoid taking St. John's wort.

In the past, St. John's wort was mistakenly classified as a MAO (monoamine oxidase) inhibitor. MAO inhibitors have several drug interactions that may cause high blood pressure readings.

The National Institute for Health released study results that found St. John's wort to adversely interact with indinavir, a protease inhibitor used to treat HIV infection. In the NIH's study, plasma concentrations of indinavir were effected by the concomitant administration of St. John's wort.

St. John's wort may also stimulate the rejection of transplanted hearts. From this new information, scientists believe that it is likely that St. John's Wort works along a metabolic pathway (particularly one involving the liver). Thus, it may render such drugs as birth control less effective. If you are currently taking a drug that works along a metabolic pathway, you should consult your doctor before taking St. John's wort.