The WHO has defined a 'Drug' as any substance, which on entering a living organism, modifies one or more of its functions. The use of the drugs, for purposes other than the reason for its prescribed recommendation, is known as Drug Abuse.
Drug abuse, Drug dependence, Harmful drug use, and Psychoactive substance use disorder, are all various names of the same condition. People generally start abusing these substances after they get addicted to it due to medical or non-medical reasons.
Addiction is generally defined as the continuous, compulsive usage of a drug despite physical and psychological harm that it may cause to the user and the society at large.
Nowadays, the term 'Substance abuse' is used frequently due to the wide range of substances, including alcohol and inhalants, that are included under the addictive drugs profile.
Conditions that arise from the misuse of alcohol, psychoactive drugs, and other chemical stimulants, are now phrased as 'Substance use disorder', or 'Psychoactive substance disorder.' Though certain drugs (Caffeine in coffee, and tea) are harmful in a mild sense, we humans are biased towards
them, and hence are reluctant about branding its usage as addictive drug abuse.