The articles in this section apply a naturalistic, cause and effect understanding of human agency to the problem of drug-induced addiction. Drugs, including alcohol and nicotine, are often the source of behavioral problems since they have immediate and powerful effects on the neural pathways that govern behavior. Addiction is explicable as a physical, brain-based phenomenon. But understanding that the voluntary choice to use addictive substances is equally physical and brain-based, albeit influenced by situational factors, is key to effective and compassionate approaches to the prevention and treatment of substance use disorders. These points get covered in an article titled "To help addicts, look beyond the fiction of free will" written for The Scientist.