...a HUGE percentage of the herbal supplements on the shelves of health-food stores are created with herbs grown in China (and other countries with the same 'standards').
Make SURE your herbal supplements (at the VERY least) are from herbs grown in the US and certified organic or wild-crafted. AND by makers that KNOW what they're doing as far as harvesting times, correct parts of the plant to utilize and utilizing methods that extract the 'goody' in a way that it's effective. Anything less is a waste of money, and could be EXTREMELY counter-productive.
At the very best? MAKE YOUR OWN herbal supplements.