Herbs are a class of plant which are often used in seasoning food. Many herbs contain active ingredients which makes them useful as medicine. Some commercially-available drugs are based on extracts from herbs or other plants. For example, the drug rivastigmine (brand name Exelon) is extracted from daffodil bulbs. Many dietary supplements also contain active ingredients extracted from herbs or plants. For example, ginkgo biloba, sold as a memory-boosting supplement, is extracted from the plant of the same name.