While there is some nuance to this issue, the short answer is that yes, addiction is a mental illness. While addiction does start with a choice to drink or use certain drugs, the mechanisms that make someone predisposed to addiction are inherent and not chosen. The official name for addiction is substance use disorder, and this is because it is a mental disorder, not a personal failing or a character flaw. Moreover, the fact that addiction is not a choice makes it even more important that veterans seek professional help.