Manufacturers of herbal medicines do not have to guarantee that the product contains what is on the label or in what amount. In fact, when tests were conducted on some of the herbs purchased in stores, many did not contain any of the active ingredient listed on the label. And, even if the herb itself is safe, herbs can be contaminated with potentially dangerous ingredients that can result in illness or even death. Some herbs may have adverse effects with some diseases. For example, some have been shown to increase blood glucose levels.
Herbs can also cause interactions with other prescription medication.
For example, ginkgo, ginger, ginseng, garlic, and feverfew may alter bleeding time and should not be used by people taking blood thinners. In addition, most herbs have not been tested in well-designed studies. A lot of the information is testimonial, meaning that someone used the herb and claimed that it improved their disease or condition. For information to be reliable, products need to go through the same rigorous scientific studies as medications to determine their usefulness and safety. The lack of clinical studies often leaves health care professionals with little or no reliable information about many of the herbs to be able to inform you of the dangers or benefits.