Downvote if you don't like the post, but we shouldn't police this.
Legal issues are out of scope here; it's up to individuals to know whether or not particular substances are legal in their jurisdiction. The most we should do here is edit in a disclaimer.
Same for medical. I don't know what specific types of drugs are considered highly dangerous and which aren't, or how much use is considered addiction or not, but that's not for us to decide. That's between the user and their doctor.
We also have to consider there's different norms across the world for substance use. I'm from the US, where marijuana is only legal in some states, and that very recently. If we think OP is from a state where it's still not legal should we close it? And what about cigarettes, alcohol? Vaping? These all have dangers too but are more widely socially acceptable.
In this question, OP feels he is being safe and is not at risk of harm or addiction. So it does not appear to be a concern of imminent danger (whether to self - where we'd remove and escalate to CMs, or to others - where we'd remove probably as R/A).
If we did get a question about clear substance abuse (not just use) like, say, "how to ask partner to stop complaining that I get blackout drunk every night of the week" - well, I would expect a bunch of frame challenges :p Depending on the details, I could also see such a question being closed as "needs professional help". But that's something we decide post-by-post.
I agree that pressuring others into partaking of anything is not ok, but I don't think we need to specifically call out drugs here - for instance, it's also inappropriate if the person is vegan and the "substance" is meat. Depending on the amount of pressure, it could be considered harassment and thus violating the CoC (like with PUA), or just a "convince" question which we've discussed are not generally a great fit for the site.
As far as HNQ... we'll cross that bridge if we come to it, but we do have the option now to remove a question from the sidebar if it's generating a lot of trouble.
Prior work on IPS meta:
I also searched around on the network to see if other sites had similar discussions:
Drugs shouldn't be excluded, and it's not the community's job to take a stance, especially if it's more politically or ethically driven rather than driven by curiosity or knowledge.
Travel.SE considered making a tag specifically for recreational substances (though apparently they never went through with it?), and they do have questions referencing recreational drug use.
Chemistry.SE can get questions regarding controlled substances. They don't ban them, but added to their help/on-topic that they don't discuss legality.
Lifehacks.SE suggests downvoting and flagging.
Last but certainly not least, Main Meta: Dealing with questions of nefarious intent:
I think that there are five levels of action that you can take:
- Just answer the question without comment. Who are we to pry into other people's business, which may be confidential?
- Do nothing. The original poster won't get an answer and will have to try somewhere else.
- Leave a comment indicating that you think this is "evil" and asking for more information as to why the asker wants to do this. Then you can choose whether or not to answer the question based on their response.
- Down-vote the post, and preferably leaving a comment that explains why to the poster.
- (The nuclear option:) Flag the post as spam, offensive, or just in need of moderator attention.
Basically, what I'm saying is that you have to treat each post on its own merits.
So I think this stance is consistent with how the rest of the network deals with such topics.