Terms such as addiction and dependency are frequently used to describe patterns of illicit drug use. However, there are no universal definitions of these terms and they are frequently used inconsistently and interchangeably. As a result, it is it difficult to estimate the number of drug users who can be described as addicted or dependent. Addiction tends to refer to dependence on a particular drug or drugs, which has developed to the extent that it has a severe and harmful impact on an individual drug user. The term implies that the drug user is unable to give up drug use without incurring adverse effects.