Common names for herbs overlap, causing confusion as to the proper identity. Even herbs that are labeled correctly may contain extraneous material from another, more dangerous, herb. Herbs may be picked at the wrong stage of growth or be handled incorrectly after harvesting, causing them to develop detrimental qualities. Buy herbs only from reputable suppliers. Buy only herbs that are labeled with their botanical name.
Botanical names are specific, but the same common name can refer to several different plants.
If you grow the herbs, be meticulous about keeping different plants separate when you harvest and dry them, and obsessive about labeling. A simple is one herb. The more herbs there are in a formula, the more likelihood there is of unwanted side effects. Understandably, the public seeks combinations, hoping to get more for less. But combining herbs with the same properties, such as goldenseal and echinacea, is counter-productive and more likely to cause trouble than a simple.