Abuse (see Substance abuse)

Addiction
Addiction is a chronic brain disease caused by changes in the brain's "reward circuits" (i.e. how the brain processes information about pleasurable experiences).  These changes are caused by the use of addictive substances. Addiction is diagnosed by learning if the patient exhibits behaviors considered symptomatic of addiction. 

Addictive substance
An addictive substance is one that causes changes in the neurons (nerve cells) in the brain.  These changes affect the brain's "reward circuits" or "pleasure pathways," the information pathways that tell the brain when something (a substance or an event) is pleasurable.

Anesthetic
A substance that causes lack of feeling or awareness. A local anesthetic causes loss of feeling in a part of the body. A general anesthetic puts the person to sleep.

Chronic
A chronic condition is one that lasts a long time, possibly for life.  The U.S. National Center for Health Statistics defines chronic as continuing for three months or more.

"Cold turkey"
A slang term for suddenly and very rapidly reducing the amount of an addictive substance one takes, or stopping completely; this process usually produces severe withdrawal symptoms.

Metabolism
Metabolism refers to the entire range of biochemical processes that occur within a living creature.  Often the term is used to refer specifically to the breakdown of food and its transformation into energy.

Opioids
Opioids are a class of drugs often prescribed for pain control that are especially addictive. They include opium, codeine, heroin, hydrocodone, methadone, and morphine, among others. 

"Pleasure pathways"
"Pleasure pathways" (also called "reward circuits") are the information pathways in the brain that produce and process information about whether an experience (such as using a drug) is pleasurable.  They are affected and altered by addiction.

Relapse
A relapse means the signs and symptoms of a disease return after a patient has enjoyed a period of time without them.

"Reward circuits" (see "Pleasure pathways")

Substance abuse
Substance abuse is the continued use of a substance even though it causes harm to the user; people are considered to be abusing a substance if, during a twelve month period, it causes them to: ignore normal professional, educational, or social responsibilities; become a danger to themselves or others; have legal problems; and/or continue to use it despite the problems it creates.  Substance abuse is a less severe condition than addiction, but still a serious problem.

Tolerance (of a drug)
Tolerance means needing increased amounts of a substance to feel its effects or feeling a decreased effect when using the same amount.  Addictive substances generally create a tolerance for them within the person using them.

Treatment
Treatment for drug addiction depends on each patient's specific situation, but usually includes both medications and psychological counseling.  It is generally thought of as a three-stage process: initial detoxification (withdrawal) designed to get the drugs or alcohol out of patients' systems and eliminate or minimize the symptoms they have produced; rehabilitation, in which patients' psychological and emotional problems are addressed; and long-term continuing care, which continues patients' psychological care in an attempt to minimize relapse.

Twelve-Step Program
Twelve-Step programs are popular rehabilitation and continuing care programs offering mutual support and assistance given by people recovering from addiction and alcoholism to others in the same condition.  They are based on a number of psychological principles and have a strong history of success. 

Withdrawal symptoms
Withdrawal is another name for the detoxification stage of addiction treatment, in which rapid withdrawal from an addictive substance (i.e. suddenly reducing the amount of the substance one takes or stopping completely) can produce extremely unpleasant symptoms, including pain, nausea, cramps, tremors, etc.