It is psychologically addictive as opposed to an addiction which would create a physical dependency in your system. Nicotine for instance doesn't really induce much of a "high" or "euphoria" (many report essentially no effect after prolonged usage). The reason stimulants like adderal can be addictive is that for many they induce an objective euphoria that upon self-conditioning can be incredibly difficult to stop taking the drug even though it doesn't technically have negative effects after stopping for a few days.

Anyone who has suffered from depression or similar and taken an adderal for the first time will understand. It takes many bad feelings and replaces them with an almost manic productivity. There are downsides, but they commonly outweigh the negatives one was experiencing without the drug.