The only reason to have restrictions is precisely to keep people from harm. The tricky word here is "supposed", that depends on how these restrictions are implemented and that should be for the moderators to judge.

If you are giving experience about your past opiate use, I see no problem with that. If I was moderating, I would not even consider banning such a talk - unless you were encouraging irresponsible use.

Point is, some substances have more risk of hurting you than others, or to develop a heavy and potentially harmful habit. Talk about these substances MAY or MAY NOT encourage/endorse reckless use or the acquisition of dangerous addictions.

Talk about these is discouraged, or watched, not necessarily banned. I always took it as it depended ultimately on the judgement of moderators.