The term "addiction" is used in many contexts to describe an obsession, compulsion, or excessive psychological dependence, such as: drug addiction (e.g. alcoholism), video game addiction, crime, money, work addiction, compulsive overeating, problem gambling, computer addiction, nicotine addiction, pornography addiction, etc.
In medical terminology, an addiction is a chronic neurobiologic disorder that has genetic, psychosocial, and environmental dimensions and is characterized by one of the following: the continued use of a substance despite its detrimental effects, impaired control over the use of a drug (compulsive behavior), and preocupation with a drug's use for non-therapeutic purposes (i.e. craving the drug). Addiction is often accompanied the presence of deviant behaviors (for instance stealing money and forging prescriptions) that are used to obtain a drug.
Tolerance to a drug and and physical dependence are not defining characteristics of addiction, although they typically accompany addiction to certain drugs. Tolerance is a pharmacologic phenomenon where the dose of a medication needs to be continually increase in order to maintain its desired effects. For instance, individuals with severe chronic pain taking opiate medications (like morphine) will need to continually increase the dose in order to maintain the drug's analgesic (pain-relieving) effects. Physical dependence is also a pharmacologic property and means that if a certain drug is abruptly discontinued, an individual will experience certain characteristic withdrawal signs and symptoms. Many drugs used for therapeutic purposes produce withdrawal symptoms when abruptly stopped, for instance oral steroids, certain antidepressants, benzodiazepines, and opiates.
However, common usage of the term addiction has spread to include psychological dependence. In this context, the term is used in drug addiction and substance abuse problems, but also refers to behaviors that are not generally recognized by the medical community as problems of addiction, such as compulsive overeating.
The term addiction is also sometimes applied to compulsions that are not substance-related, such as problem gambling and computer addiction. In these kinds of common usages, the term addiction is used to describe a recurring compulsion by an individual to engage in some specific activity, despite harmful consequences, as deemed by the user himself to his or her individual health, mental state or social life.
Not all doctors agree on the exact nature of addiction or dependency however the biopsychosocial model is generally accepted in scientific fields as the most comprehensive theorem for addiction. Historically, addiction has been defined with regard solely to psychoactive substances (for example alcohol, tobacco and other drugs) which cross the blood-brain barrier once ingested, temporarily altering the chemical milieu of the brain. However, "studies on phenomenology, family history, and response to treatment suggest that intermittent explosive disorder, kleptomania, pathological gambling, pyromania, and trichotillomania may be related to mood disorders, alcohol and psychoactive substance abuse, and anxiety disorders (especially obsessive–compulsive disorder)." However, such disorders are classified by the American Psychological Association as impulse control disorders and therefore not as addictions.
Many people, both psychology professionals and laypersons, now feel that there should be accommodation made to include psychological dependency on such things as gambling, food, sex, pornography, computers, work, exercise, spiritual obsession (as opposed to religious devotion), cutting and shopping so these behaviors count as 'addictions' as well and cause guilt, shame, fear, hopelessness, failure, rejection, anxiety, or humiliation symptoms associated with, among other medical conditions, depression and epilepsy. Although, the above mentioned are things or tasks which, when used or performed, do not fit into the traditional view of addiction and may be better defined as an obsessive–compulsive disorder, withdrawal symptoms may occur with abatement of such behaviors. It is said by those who adhere to a traditionalist view that these withdrawal-like symptoms are not strictly reflective of an addiction, but rather of a behavioral disorder. However, understanding of neural science, the brain, the nervous system, human behavior, and affective disorders has revealed "the impact of molecular biology in the mechanisms underlying developmental processes and in the pathogenesis of disease". The use of thyroid hormones as an effective adjunct treatment for affective disorders has been studied over the past three decades and has been confirmed repeatedly. Modern research into addiction is generally focused on Dopaminergic pathways. There is great and sometimes heated debate around the definition of addiction with parties falling into two main camps the Disease model of addiction and the behaviorists, explanations of various models can be found in the article on Drug rehabilitation.