Two out of three Americans who use medical herbs do so without taking note of the evidence-based indications. Roughly twelve percent of the population behave this wrong way, according to a US-wide representative survey in more than thirty thousand adults. The use of ten different herbs has been surveyed. Misuse has been found in nine of them, the only (full) exception being Echinacea. In best case, a lot of money is wasted. But there is likely to be a lot of worse cases where the herbs bring more harm than benefit.
Important to know
Herbs have effects. That's why we use them. The effect is not magic but based upon chemical substances. Every substance that has a wanted effect can and will also have one or more unwanted side effects. Herbs can be very potent such as the beautiful Rauwolfia shown here. The plant is used in folk medicine and by the pharmaceutical industry for drugs that reduce blood pressure. - (Picture by prolix6x @ Flickr)
Do consult your doctor whenever you use herbal medicine. Or ask your pharmacist or druggist. At least consult the internet.
Don't use a herbal medicine just because your friend told you, or because all use it, or because it is said to be effective, or because you took it earlier and it helped you then.