An addiction is something that is hard to stop even though it is interfering with your life. You can be addicted to substances such as alcohol or drugs (e.g., cocaine, heroin, morphine, nicotine), or to activities such as eating, gambling, shopping, video games, or sex.
Addiction can be tricky to diagnose, but the presence of the four C's (craving, negative consequences, loss of control, and compulsion) is a good indication that an addiction is present.
When someone you care about develops an addiction, there may be a tendency to take responsibility for him or her. This may be indicative of an issue with codependency.