The fifth precept concerns the use of intoxicants. An intoxicant is anything which produces a state of excitement or stupefaction and diminished mental or physical capability. It is something that we use, or allow, in order to escape from the boredom or pain of the present moment. Thus almost anything can become an intoxicant, not just alcohol and drugs, but activities such as shopping, watching TV, exercise, sex, reading, eating, anything that we turn to as a means of avoiding how we feel.
The Buddha taught that all conditioned things are a false refuge and that true happiness lies in the knowledge of that which is unconditioned. To cloud, or intoxicate, the mind takes us away from knowing the immaculacy of the present moment, which does not need enhancing, and indeed cannot be enhanced, by the use of intoxicants.
This precept is expressed as not selling the wine of delusion. Whatever we do sets an example to others, and if we allow ourselves to be intoxicated it encourages others to do the same. We should never underestimate the good that flows into the world by our efforts to live an awake life.