After input from various comrades, I've decided to improve the rule with some explanation, this is my latest suggestion:
Rule 4: Do not promote drugs/alcohol/tobacco/weed/psychedelics/inhalants or any other substance that may be abused. We do not discuss the personal use of these substances out of consideration for comrades who might be affected by substance abuse or have bad experiences related to them. We understand that some substances may be used [medically|(for treatment)] in different cultures, but we think that this community is not the appropriate channel to receive medical advice.