Herbal supplements are non-pharmaceutical non-food substances marketed to improve health. Herbalism (herbal medicine, botanical medicine) is the use of plant-derived substances, and sometimes other environmental substances, to treat or cure medical conditions. Herbalism recognizes that pre-industrial cultures had a great deal of practical medical knowledge, most of it botanical, and seeks to make use of this. Definitions are problematic. There are no unified practices, no enforceable standards for strength or purity, and relatively few guidelines for practitioners. Also, there is no clear definition of what an "herbal remedy" is. A large number of currently available drugs are originally plant-derived, which means herbalism is basically pharmacology's petulant, stubborn great grandmother.
Many studies have been done of herbal medications. Unfortunately they often lack good documentation, quality, and suffer from not having analyzed the substance studied. Because of the lack of quality control and regulation, it is difficult to assess what the effect of many herbs is, or even what people may be taking, given the label often fails to match the content.
Given these limitations, a summary of studies of some popular supplements is listed below:
Milk Thistle seems to have proven results in reducing liver inflammation in children undergoing chemotherapy.
Ginkgo is sold as a "memory aid" and a treatment for Alzheimer's disease. Studies show mixed results, with a possibility of it being better than placebo
Saw palmetto: marketed as a treatment for benign prostate disease in men, studies show some effect greater than placebo, at least in the short term.
St. John's Wort: used for depression, data show short-term efficacy over placebo for mild to moderate depression. (May cause cataracts, though this has not been proven.)