Since concentration of ingredients in these preparations is not precisely controlled, accidental overuse of herbal medicines is possible. Also, distributors generally do not disclose any trace contaminants, such as pesticides, which may have been used while growing the plants. No chemical put into the body works without interacting with other chemicals. Unfortunately, most of these effects of herbal medicines have not been scientificallly documented. Clearly herbs are more than just food and spices.
Herbal medicines contain pharmacologically active chemical ingredients, in other words drugs.
Many such effects cannot be predicted, only documented by careful investigation of persons using them. If you take herbal medicines, insist that whoever sells you these medicines provide you with the complete list and precise concentration and type of all pharmacoactive ingredients, all inactive ingredients, and all trace contaminants. This is what is required of your doctor and your pharmacist. You should expect no less from your herbalist.