In several dominant drug classification systems, these four types of classifications form a hierarchy. For example, the fibrates are a chemical class of drugs (amphipathic carboxylic acids) that share the same mechanism of action (PPAR agonist), mode of action (reducing blood triglycerides), and are used to prevent and to treat the same disease (atherosclerosis). Conversely not all PPAR agonists are fibrates, not all triglyceride lowering agents are PPAR agonists, and not all drugs that are used to treat atherosclerosis are triglyceride lowering agents.