A recreational drug is one that is used for pleasure rather than for medicinal, religious or other purposes.
For various reasons - mostly those of public order, public health or community morays it is fairly common for the production, sale, possession and use of recreational drugs to be (sometimes heavily) restricted.
Unfortunately what counts as a recreational drug depends very greatly on circumstance - which many legislators are too stupid or lazy to understand - and a substance which is used for recreational purposes may have useful applications in other fields which can be unreasonably impeded by laws intended to prevent leisure use.
Also, those who want some kind of historical verisimilitude in their campaign setting should be aware that, religious taboos aside, prohibition of recreational drugs was historically very rare. Most standard fantasy settings appear to operate to modern cultural values and have the majority of such drugs heavily restricted - possibly to avoid censorship - but in reality this should be far more the exception than the rule. If anything, the average medieval state would be more likely to sell a monopoly in the trade than prohibit it outright.
Game and Story Use
- Every culture has its drug(s) of choice - and will usually have culturally bound ways of accomodating their use. Disruption of these structures, or introduction of a foreign drug, is likely to cause social problems.
- Where you have multiple species, differing biochemistry may radically alter what constitutes a drug - catnip, for example, could be major social problem for cat people but a non-issue for humans. Even more radically the theobromine found in chocolate is far more psychoactive (and toxic to many mammals than it is to humans. Travellers had best be very careful what they carry about with them.
- Where prohibition exists, circumventing it is an obvious source of adventure profit but can be a source of considerable values dissonance. After all cocaine smugglers look like an acceptable target to modern eyes, but we wink at the idea of a 1920s boot legger or rum-runner.
- Probably a good treasure, especially if you like to promote in party roleplaying.
- Recreational drugs can also be used as a form of surrogate currency in an appropriate black market.