Tamora Pierce's The Circle Opens quartet features 'dragonsalt,' a highly addictive and illegal drug that some very not-nice people use to keep a mage under control. To the non-magical, it can make them feel like they're stronger and thinking more clearly. When I first read it, I loved the fact that it was entirely new and that it was so clearly linked to that world - they had what amount to police-mages who could detect its influence in magic used in crimes, and the name was pretty explanatory.
In short, when writing fantasy including magic or law enforcement, considering whether something is legal, whether it has different effects on magic and non-magic users and different sentient/sapient species, its addictiveness, value and potential deadliness can all make choosing a fictional drug easier. Legality could be directly related to any one of those things, particularly if something is renowned for increasing violence, addictiveness, potency, or a potential poison. At the same time, if certain drugs have certain medicinal properties - opiates being a prime example - that can cause other problems within that society.
Drugs - whether medicinal, recreational, or poisonous - are a brilliant way of world-building, and I agree with the others that modern names would often throw me when dealing with a secondary world, if not with an urban or sci-fi one (depending on whether the sci-fi is human-based or not), unless it's there deliberately as a point of significance, such as it turning out that one character who consistently refers to 'milk of the poppy' as morphine or heroin is actually from 'our' world and trapped in that one.
At the same time, finding out old or ancient names for drugs or medicines can work well for secondary worlds, and also extinct plants that may or may not have had the properties attributed to them by historical records. Or using plants which were believed to have properties - such as the self-explanatory fleabane - and giving them those properties.
Just my thoughts.