Whether it's sipping coffee or shooting smack, people have a penchant for ingesting substances that alter their brain chemistry. And that can lead to drug dependence. But which drugs are most addictive? As Eric Bowman points out in an article in The Conversation, the answer to that question is not as cut and dry as it may seem. From varying points of view, a drug's addictiveness can be judged by its street value, the harm it causes, withdrawal symptoms, or how pleasurable its effects are, among other factors. For his list of the five most addictive drugs, Bowman relies largely on research gleaned from surveying addiction experts. Here's what he came up with (in order of addictiveness):