Aversion therapy is a kind of therapy used to help people quit habits like smoking or gambling. It works by making the person associate something unpleasant with their addictive behavior. For example, if someone is trying to quit smoking, they might be asked to smoke while also being exposed to something that makes them feel sick. After a few times of doing this, just the act of smoking becomes associated with feeling sick. This makes the person less likely to continue their addictive behavior.