Maybe taxes on these products should be ring fenced to pay for help and support with treatment, and ensure this is fully available.
Also as education is key, ensure lessons are giving due warnings as to the dangers, as well as benefits (sensible social drinking is fine for example) The dangers are also backed by science research and give schools, colleges etc acess to the various papers and research to back it up. Let people make their own choices.
I guess the difference is what people do to their own bodies is their own choice and responsibility in a way, if they take drugs or drink and then drive, maim or kill someonme as a result then the punishment NEEDS to fit the crime.
Personal responsibility and actions have consequences need to be taught from an early age.
In the case of smoking tobacco then the dangers of passive smoking are also well known, perhaps that needs a different approach, smoking in doors is banned in many places to protect others
I would also guess by making any product legal, the concentration and purity can also be controlled and regulated, I have seen programs in the UK on fake products, so a fake medication, can be made in unhygienic uncontrolled conditions, with the weight made up with other products, the end buyer has NO IDEA what they are actually getting.
This has benefit for those making illegal products and zero benefit to the end user.