Terms such as “addiction” and “dependency” are frequently used to describe patterns of illicit drug use, but there are no universal definitions of these terms. 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. Drug dependency can refer to physical and/or emotional dependency, and drug users may experience one or both forms. However, as a result of the inconsistent use of the terms, it is difficult to estimate the number of drug users who can be described as addicted or dependent.