The authorities said they had conducted tests on top-selling store brands of herbal supplements at four national retailers — GNC, Target, Walgreens and Walmart — and found that four out of five of the products did not contain any of the herbs on their labels. The tests showed that pills labeled medicinal herbs often contained little more than cheap fillers like powdered rice, asparagus and houseplants, and in some cases substances that could be dangerous to those with allergies.