Eh. As long as people aren't using this place to distribute I think it would fall firmly within the bounds of freeze peach. Basically the same boundary as the guns community, or a potential sex work community. I'd be more worried about the moral issues than the legal issues. The potential of promoting self-harm, the downstream oppression and violence inherit in black market drug trades, etc.

I firmly believe having a forum and support network is a much better alternative than having people isolated though, that not every case of drug use is harmful, and that even when it is harmful, these are exactly the situations where intervention and support are a good thing.