I have been using Clark's parasite program and some other of the herbs she suggested for more than 25 years with no problems even when I have taken more green Black-Walnut and Wormwood than she called for. She wrote that people could experiment a little with the dosage and back off from a higher dosage if they seemed to develop problems. It is my opinion that Wormwood taken in small amounts is not harmful. Taking larger amounths of Wormwood over a longer period of time, such as a habit of drinking absinthe, can be harmful.