Codependency is often (although not solely) the result of living with an addict or alcoholic. It forces the codependent to take responsibility for their partner's illness and provide them with help at the cost of their own well-being. It is, in most part, related to the lack of healthy boundaries in the relationship which ultimately results in a total loss of self.
In order to treat codpendency, the codependent needs to be taught the importance of boundaries, how to construct them and, more importantly, how to maintain them. They need to stop their self-defeating behaviours and learn how to value themselves for who they are.
This is different to Family Therapy (although there are often crossovers) as it concentrates purely on the codependent regardless of the addicted partner.
Codependents often feel guilty, sad, fearful or angry depending on the moods of those around them. They often have no concept of where they end and another person begins.
However, as with any addiction or personality disorder, one to one counselling can be an extremely powerful and productive way to overcome these unhealthy behavioural and thought patterns and improve one's personal well-being together with any damaged relationships.