[Pharo]

It depends on how you define "disease".
Addictions are psychological, but they're also physiological.
Any activity that produces a strong endorphin rush can be addiction, although drugs produce this much easier than other things.
If something is highly pleasurable, we try and repeat it. Eventually, this can take priority over other activities, and become harmful.
But it is not a disease in proper sense, since it isn't a harmful outside virus or bacteria or etc. You could call it a disorder, though.