Medications are typically administered to achieve therapeutic effects. Some drugs can modify an individual's mood and perception, frequently resulting in various enjoyable experiences. However, this can result in drug dependency, a condition marked by continuous drug use despite potential negative consequences. Drug dependency primarily falls into two categories: psychological and physical dependence. Psychological dependence occurs when the pleasurable feelings induced by the drug significantly influence the individual's desire for repeated use, potentially leading to relapse. In contrast, physical dependence involves the manifestation of withdrawal or abstinence symptoms when the drug is suddenly stopped or an antagonist is introduced. This disruption interferes with the body's homeostatic balance.

Take nicotine, a main ingredient in tobacco, as an example. It can cause both psychological and physical dependency. A person trying to quit smoking may experience withdrawal symptoms. Successfully managing these symptoms may allow temporary cessation of smoking. However, over time, feelings of depression and psychological cravings may arise, leading to a relapse.