Social animals use affect as a means of communicating internal states in order to coordinate communal efforts. It is impossible to modify one without the other. If one's affective system is bypassed, he becomes insulated from empathic influence. The primary complaint of the family of the addict is that he or she has become inaccessible. The development of human language provided us with the first major revolution in affect modulation, a kind of Pleistocene high-tech affect management.
Language provides a device for extremely powerful magnification of affective response.
As a tool for this purpose, it has been in use for hundreds of thousands of years, after much research and development by pre-Homo sapiens. Looking at drugs as new technology, it will be easier to see why we are so wary of their introduction. I recently had the privilege of touring a small winery near Macon in France, where the vintner had amassed a remarkable collection of vineyard and wine-making tools and machinery dating back hundreds of years. These included dozens of odd-shaped little hand axes, which had been used to prune vines for centuries. One day, someone invented a simple pruning shear, which enabled one worker to do in a day what had previously taken four.