addict, addiction
An addict is a person who seeks reward from a substance or behavior with impaired decision making and behavior despite harms caused by the behavior. Because of the stigma associated with addict, use person-first language (a person with an addiction or substance use disorder, a person who uses drugs, or a person in recovery) unless in a direct quote.
From Reporting On Addiction:
People with addiction use substances or engage in behaviors that become compulsive and often continue use despite harmful consequences. Prevention efforts and treatment approaches for addiction are generally as successful as those for other chronic diseases.
Severe and chronic substance use disorders may be referred to as an addiction. Addiction is a lot like other chronic diseases, such as heart disease, asthma, or cancer. They all disrupt the normal, healthy functioning of your body, have serious harmful effects, are treatable, and in some cases preventable. They are also progressive meaning if left untreated, they can become severe and may lead to death. Lifestyle changes can help with these diseases, but treatment often requires a trained medical professional.
Also see recovery, rehab, and substance use disorder.