Definition of addiction: Addiction is repeated involvement with a substance or activity, despite the substantial harm it now causes, because that involvement was (and may continue to be) pleasurable and/or valuable.
How does this definition compare to other terms that describe addiction?
Addictive behavior may be the broadest term, although people use it interchangeably with addiction. Both terms suggest that substances as well as activities can be addictions. Addictive behavior includes behaviors directly related to an addiction (e.g., injecting heroin, purchasing drugs). It also includes behaviors that are indirectly related to an addiction (e.g., secrecy surrounding use, dishonesty). Although perhaps any substance or activity could become addictive, usually the substance or activity is one that has an emotional impact. You are much more likely to get addicted to alcohol than water or (caffeine free) soda. Likewise, gambling is a behavior that can lead to an emotional high with each win (or near win). Therefore, it is more likely to become an addictive behavior than reading a book.
Chemical dependence refers to addiction to any intoxicating substance. Thus, it excludes activities addictions. It also doesn't include nicotine and caffeine (or food). Although both nicotine and caffeine have an emotional impact, people do not normally consume them in doses that dramatically alter their state of consciousness. Interestingly, some treatment centers turn a blind eye to treatment participants who continue to practice other dangerous addictions such as smoking and over-eating while attending treatment. These treatment centers only consider "chemical dependence" to be an addiction worthy of treatment. Yet smoking and overeating lead to premature death much more often than alcohol and other substances combined. (Mokdad, Marks, Stroup & Gerberding, 2004).
Psychoactive substance use is a term used by clinicians to distinguish substance use that has psychological effects, as opposed to consuming other substances that do not have psychological effects (e.g., water, most medications).
Drug addiction and substance addiction are synonymous terms that limit addiction to a drug or intoxicating substances.
Activity addiction, behavioral addiction and process addiction are synonymous terms that limit addiction to activities. The term process addiction is somewhat misleading because substance addictions involve processes as well. Therefore, we refer to these addictions as activity addictions.
Experimentation is a term that describes someone's first few experiences with substance use. However, from a "zero tolerance" perspective, any substance use is actually substance misuse. Nonetheless, misuse is more often reserved to suggest a level of use that is problematic (such as getting drunk at your sister's wedding), but not of sufficient intensity and duration to merit the terms abuse, addiction, or dependence.
Substance abuse and substance dependence are older diagnostic terms. These older terms attempted to define the severity of addiction. Abuse was considered a milder form of addiction. Dependence was more severe. Our definition does not make sharp and arbitrary distinctions between use, abuse, and dependence. The severity of addiction is highly variable and changes over time. Moreover, these terms were only applicable to substances and did not include activity addictions.
Substance-related and Addictive Disorders is the current diagnostic label that clinicians use. The diagnostic criteria for these disorders are somewhat similar to our definition of addiction. However, gambling is the only activity addiction recognized by the DSM-5 (APA, 2013). The DSM-5 also lists "internet and gaming disorder" as a potential diagnosis for future consideration.