Something that is important to keep in mind for such statements is that scientific research rarely speaks in absolute terms. It takes a lot for something to get to the point of scientific law. Gravity, for example, is still in scientific theory territory. In order for the scientific community to make the statement "people with ADHD cannot become addicted to stimulants", neurobiology and neurochemistry would need to be better understood than the force that has been officially described in scientific literature for 350 years. If any possible avenue exists to cause addiction, the absolute statement would not be scientifically accurate.