Studies have also shown that St. John's Wort may actually decrease the effect of many HIV drugs. In fact, a number of prescription drugs may be actually be weakened in persons who are also taking St. John's Wort. Such drugs include many oral contraceptives and cancer fighting drugs. For this reason, as well as the reasons noted above, it is important to discuss the use of this product with your physician if you are taking any type of prescription medication.

Definitely at the far end of the herbal supplement safety scale you will find the now wildly popular green tea, and its concentrated cousin, green tea extract. Green tea products seem to carry few risks and they are attracting a great deal of media buzz these days. Who has not heard of the "Oprah green tea diet?" Green tea, unlike black tea, or oolong tea, is not fermented and therefore retains all of the active constituents that are high in antioxidants essential in the prevention of cancer. Green teas and extracts are also believed to be effective in lowering cholesterol, and they even have been used in the control of genital warts.

Just how much green tea one needs to drink in a day's time, however, seems to vary depending upon which expert's report you choose to read. Some researchers believe that a person would have to drink in excess of 10 cups of green tea per day in order to derive any benefits from the product. Most, however, believe that 3 to 4 cups of tea per day is adequate. Still, for some individuals, even green tea may be hazardous to their health.

Many of the green tea products contain caffeine, and should be avoided by heart patients, kidney patients, pregnant women, and persons with anxiety disorders. In addition, green tea has been found to interact with the anti-psychotic drug Clozapine. This drug is used in the treatment of schizophrenia and, in some cases, especially if the drug is taken shortly (roughly 40 minutes) after drinking green tea, its medicating effects may be reduced, and in some cases the person's psychotic symptoms may worsen.