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 brain chemically.  How do drugs work?  In the brain, drugs may either intensify or dull your senses, alter your sense of alertness, and sometimes decrease physical pain.

Here are a few warning signs that someone may have a substance abuse problem:

relying on drugs or alcohol to have fun, forget problems, or relax, having blackouts, drinking or using drugs while alone, withdrawing or keeping secrets from friends or family, losing interest in activities that used to be important,performing differently in school (such as grades dropping and frequent absences), building an increased tolerance to alcohol or drugs — gradually needing more and more of the substance to get the same feeling, lying, stealing, or selling stuff to get money for drugs or alcohol.

It’s usually hard for people to recognize they have a problem, which is why friends or family often step in. Quitting is hard to do, and many people find they can’t do it without help.  By talking with to someone you trust, you don’t have to deal with your problem and secrets alone.

Today, the term  addiction can also be applied to compulsions that are not substance-related.  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 individual health, mental state, or social life.  Some examples include: gambling, food, sex, pornography, computers, video games, internet, work, exercise,  watching TV or certain types of non-pornographic videos, spiritual obsession, pain, cutting and shopping that are also considered psychological and physiological addictive substances or behaviors.   These addictions may cause feelings of guilt, shame, fear,hopelessness, failure, rejection, anxiety, or humiliation symptoms associated with, among other medical conditions, depression and epilepsy.

The related concept of drug addiction has many different definitions. Some writers give in fact drug addiction the same meaning as substance dependence, others for example provide drug addiction a narrower meaning which excludes drugs without evidence of tolerance or withdrawal symptoms.

The American Society of Addiction Medicine has this definition for Addiction: Addiction is a primary, chronic disease of brain reward, motivation, memory and related circuitry. Dysfunction in these circuits leads to characteristic biological, psychological, social and spiritual manifestations. This is reflected in the individual pursuing reward and/or relief by substance use and other behaviors. Addiction is characterized by impairment in behavioral control, craving, inability to consistently abstain, and diminished recognition of significant problems with one’s behaviors and interpersonal relationships. Like other chronic diseases, addiction involves cycles of relapse and remission. Without treatment or engagement in recovery activities, addiction is progressive and can result in disability or premature death.

According to the current Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), substance dependence is defined as:

Substance dependence can be diagnosed with physiological dependence, evidence of tolerance or withdrawal, or without physiological dependence.