The word you are looking for is pleasure. The only types of drugs that are 100% illegal are drugs that have no purpose besides making you feel pleasurable sensations. Horrible side effects (e.g. chemo) and high chance of addiction (opioids, amphetamines, etc) and more are all allowed as long as the purpose of the effect of the drug is not (solely) pleasure.

Alcohol, and increasingly in some parts of the world Cannabis, are the exceptions (I understand both of these substances have real and potential uses in healthcare, but they are perceived as recreational). These are legal or quasi-legal only because they are both already in wide use and getting society on board to enforce a ban is difficult to impossible (depending on the society, a few do) . Tabacco is also on the list, but seems to be falling off somewhat.