In the previous version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), which was used until 2013, substance abuse was classified on the multi-axial system as an Axis I disorder, which included clinical disorders such as major depressive disorder, schizophrenia, and bipolar disorder.
However, with the release of the DSM-5 in 2013, the multi-axial system was eliminated and the classification of substance use disorders was changed. Substance use disorders are now classified as a single disorder in the DSM-5 and are further classified by severity, ranging from mild to severe based on the number of diagnostic criteria met by the individual.
In the DSM-5, substance use disorders are classified under the “Substance-Related and Addictive Disorders” category, which includes disorders related to the use of alcohol, caffeine, cannabis, hallucinogens, inhalants, opioids, sedatives, hypnotics, and stimulants. Therefore, substance abuse is not classified under a specific axis in the DSM-5.