The political use of mind-altering, or mood-altering, drugs
While coercive governments have always used whatever means available to enforce their will on the population, in some cases psychochemistry has become so intertwined with the political system that a chemical form of government develops. Mental influence and modification can of course be achieved through a variety of means beside psychochemistry: memetic engineering, psychosurgery, nanotechnology, neural implants etc. However, chemistry was the earliest and in many ways easiest way of achieving mental modifications on a mass level, and hence the pharmacracy label is often used to denote other mental modification societies.
The simplest forms of coercive use of psychochemicals consists of addicting the population to some chemicals, either in order to decrease their will to get rid of the current rulers (this approach usually fails because the necessary initiative for maintaining society is also drained) or as a means of control if the rulers are the only ones able to manufacture the drug. The perhaps most famous example was the Lucullus Oligarchy, which during the late 5000's controlled over 40 star systems with a caste system based on the taking of certain drugs. The Engineer caste, for example, was addicted to a certain form of time dilative nootropics, while the Player caste was addicted to various mood brighteners. The Oligarchy persisted for over 400 years until the drug monopoly was broken by invading NoCoZo traders, and the power structure imploded.
A more subtle form of pharmacracy, which is further from the traditional centralist-coercive form of government, is the use of altruzines. Altruism-enhancing drugs (or other devices) can make enough people into voluntary altruists to make many traditionally impossible social forms at least marginally stable. There are many examples of altruism enhanced anarchies in the Utopia Sphere, where the combination of massive altruism induction and automated production makes them possible. Unlike simple chemical coercion altruzine-based societies have an interest in doping all citizens with the drugs; defectors may of course want to avoid it.
The truly advanced pharmacracies use a wide variety of not just mood- but also reality-, cognition-, personality- and memory-altering drugs. Often they develop as an adaptation to harsh circumstances such as overcrowding, stress and conflicts, but develop into true pharmacracy as the chemical market expands into all parts of life. Reality becomes chemically enhanced, personality alteration an everyday procedure and emotions and values a matter of choice. If the society avoids the obvious instabilities and risks (such as actualys or widespread addiction-locking) it will tend to develop into a true pharmacracy, where individuality and views change flexibly depending on demands, fashions and the current situation. At present the best example of such a mature pharmacracy is the Sampo Association of the corewards MPA.