In this two-part analysis, I analyze Marc Lewis’s arguments against the brain-disease view of substance addiction and for a developmental-learning approach that demedicalizes addiction. I focus especially on the question of whether addiction is a medical disorder. Addiction is currently classified as a medical disorder in DSM-5 and ICD-10. It is further labeled a brain disease by NIDA, based on observed brain changes in addicts that are interpreted as brain damage. Lewis argues that the changes result instead from normal neuroplasticity (...) and learning in response to the intense rewards provided by addictive substances, thus that addiction is not a brain disease and by implication not a medical disorder at all. I argue that even if one accepts Lewis’s reinterpretation of the brain evidence, his conclusions do not follow. Relying on my harmful-dysfunction analysis of medical disorder, I defend the view that substance addiction is in fact a medical disorder and a brain disorder. In Part 1, I identify five arguments Lewis puts forward against the brain-disease view and evaluate them as arguments that addiction is not a disorder: Addiction is not a chronic, relapsing condition; There is no clear boundary between addiction and other strong desires; Negative consequences are not unique to disorders; The brain disease model does not account for behavioral addictions; and, Addiction is like love. I argue that Lewis’s arguments are invalid because they fail to take account of the context of addiction and its relation to biological design. (shrink)