In most cultures, including Western culture, herbs are used not only as a part of the treatment of disease, but also in the enhancement of life, physically, emotionally and spiritually. Plant parts, including flowers, fruits, leaves, twigs, bark, roots or seeds, are all considered usable. Until the 1930s, medical schools taught that plant drugs were the primary medicines available. Sometimes, even if you take an herb for one certain reason, there can be other unintended reactions. Natural doesn't necessarily mean safe.
Herbs have chemical properties just as manufactured drugs do.
One of the major problems with many of the herbs on the market today is that the amount and the purity of their active ingredients vary so greatly from product to product. In many cases, you do not always know how much of the herb you are really getting in each dose or if other ingredients have been added. Another problem is determining how much of each active ingredient is really safe, particularly over long-term use. There are even case reports of contaminated herbs causing death. Also, studies are being done to see how herbals react with other medications.