By Dov Michaeli MD, Ph.D We all heard this refrain; drug addicts kicking the habit, only to go through a lifetime of a constant battle to stay clean. Why is it so hard? Why is it getting progressively harder within days after quitting? Who is the “devil that made them do it”? The received wisdom for many years was that the reward system in the brain, which is the seat of all manners of addiction, is driven exclusively by dopamine receptors. But frankly, this belief had some problems. Here is a big one: the dopamine system is geared to maintaining homeostasis, which is the property of a living organism to regulate its internal environment so as to maintain a stable, constant condition. For example, exposure of dopaminergic neurons to increased concentrations of cocaine results i...