The term codependency describes a situation in which a person literally becomes emotionally addicted to another person's addiction. Some experts even refer to codependency as a "relationship addiction", because codependents often form dysfunctional, one-sided relationships with self-destructive partners. Although the phenomenon of codependency has existed for many years, a constructive definition only emerged with the rise of 12 step recovery programs such as Alcoholics Anonymous (AA), Overeaters Anonymous (OA), and Narcotics Anonymous (NA).

Researchers studying the mechanisms of addiction discovered that certain family members, romantic partners, or close friends formed unhealthy bonds with the addict. These people seemed determined to rescue or protect the addict, even to the point of self-sacrifice. Recovering addicts recognized this behavior as 'enabling', providing addictive substances in order to keep an addict from becoming completely healthy. Codependency is often defined as a maladjustment disorder, in which the codependent feeds off the emotional need created by the addict. Codependency is usually an emotional self-defense mechanism triggered by childhood experiences in a dysfunctional home marred by substance abuse or overly restrictive parents.

Many people assume that codependency is a strictly passive condition, with the codependent only performing as a servant to the addict. In reality, codependency is a passive-aggressive condition, with the enabler controlling the addict through emotional and physical manipulation. In an unhealthy relationship forged by codependency, the enabler needs the addict to remain unhealthy and dependent. While many people feel a strong need to help a loved one in a time of personal crisis, a number of codependents see themselves as martyrs or self-sacrificing heroes. Caring for an addict helps define them as people worthy of respect, which they believe they wouldn't receive under healthier circumstances.

Codependency is a learned behavior, with children observing the effects of addiction on their parents. A person who experienced a traumatic childhood involving sexual or physical abuse will often seek out a partner with substance abuse problems or anti-social behavior. The belief generated by codependency is that he or she will somehow be able to 'fix' this person's numerous issues. In actuality, these codependent relationships often crash and burn, leaving the codependent with even lower self-esteem. Since many codependents avoid interaction with healthy, well-adjusted people, the codependency cycle usually continues with a series of damaging relationships.

Codependency can be treated through psychotherapy and intervention, although it can be very difficult to convince codependents to seek help. In their minds, codependents are only performing a role others should be playing in an addict's life. Many feel their intentions are honorable, even if the results aren't always successful. Ironically, codependency can trigger addictive behavior in the enabler, creating an even more complicated relationship with the addict and others.

There are self-help programs available to address codependency, modeled after the 12 step recovery programs of AA and NA. Codependents Anonymous meetings offer sufferers an opportunity to share their experiences with others who understand the condition. Recovering addicts may also recognize signs of codependency in a family member or romantic partner and take steps towards helping that person reclaim his or her independence.