When someone abuses a drug, changes occur in the brain that bring on a feeling of pleasure. Pleasure is the reason for continuing to abuse the drug early on. These changes, however, also have a long-term effect on the brain, the National Institute on Drug Abuse (NIDA) says. These changes shift abuse to addiction. Without the drug, the pleasurable feeling decreases, and the drug is required just to get back to a normal level of pleasure. Thus, people addicted to drugs, including alcohol, suffer from a craving for the drug and usually can’t quit by themselves.

Addiction ranges from "pre-addiction" to the advanced stages of dependence. Unfortunately, many people still view drug abuse and addiction as a social problem, the NIDA says. People who are addicted to drugs, however, are not morally weak and simply unwilling to change their behavior.

Other signs include the inability to limit the amount of substance used; ongoing desire for the substance; unsuccessful attempts to stop; spending a lot of time obtaining, using, or recovering from the substance; and using despite ongoing personal problems. Medical professionals use a questionnaire developed for alcoholism as a screening tool for addiction. The questionnaire, called CAGE, asks these four questions:

• Have you ever felt you ought to Cut down on your drinking/drug use?
• Have people ever Annoyed you by criticizing your drinking/drug use?
• Have you ever felt bad or Guilty about your drinking/drug use?
• Have you ever had a drink or taken a drug first thing in the morning to steady your nerves or get rid of a hangover (Eye-opener)?

Answering yes to one or more of these questions may indicate a problem with drug abuse or addiction.

How quickly a person can become addicted to a drug depends on the person's sensitivity to the drug, but it usually takes longer than a few days. Some drugs are more addictive than others.

This is the defining feature of addiction.

Besides causing problems such as loss of a job or relationship, drug addiction can cause wide-ranging health problems. These are among the health problems related to drug abuse and addiction: heart disease, stroke, cancer, AIDS, hepatitis and lung disease, according to the NIDA. Brain changes that occur with addiction can affect memory, attention and decision-making.

Most people addicted to drugs need treatment to overcome their addiction. The goal of treatment is lasting abstinence, the NIDA says, but initial goals are to cut back on drug use, improve a person's ability to function and reverse or stop any medical problems associated with drug use. Several types of treatment are available: short-term methods lasting less than six months and longer-term programs such as methadone treatment for people addicted to opiate drugs such as heroin.

Being addicted merely reflects the fact the person has used a substance to the point at which he or she is now unable to control the use of that substance.

If a person doesn’t start change, it’s highly unlikely recovery will occur. There are several steps in the process. The first step is when the person is not interested in changing behavior. Through education and help, the person can move to the second stage. He or she now thinks about changing in the next six months. From there, the person can move to getting ready to make the change, action and maintenance (continuing the behavior change beyond six months).