Most drugs. This is definitely not going to work with heroin and methamphetamines.
Legalizing all recreational drugs isn't "harm reduction", it's creating a bigger drug addiction pandemic. Successful Harm reduction models like in Portugal have legalized no recreational drugs.
And why? Those who want drugs, can get (any) drugs today, just with bad quality and the dark sides of crime involved. Who do stuff like adding other drugs that have a higher addiction potential.
If you legalize it, all the dark sides of cartels and co vanishes and you can spend all the police money on education and therapy to fight the actual bad sides of drugs. And preventing the reasons for people to do (hard) drugs in the first place.
(But not necessarily more than other countries).
So I see a need to do further harm reduction.
Harm reduction is a series of publicly funded social and rehabilitation/substitution programs that has absolutely nothing to do with legalizing any sort of drugs. Legalization is an entire different question, just don't try to make "harm reduction" yet another buzzword for legalization.
Currently junkies need the dealers to get their supplies. So they have to support crime, to meet their needs. And they get bad quality with usually extra poisenous additives. Legalizing would immmediately reduce or remove those 2 harms.
But I agree that we should not stop there, but rather help them stop being junkies at all, with various help programms. I just happen to think it is easier to reach people in legal ways, than criminalize them. But you seem to disagree here?
Harm from drugs in the current system goes well beyond the individual user.
If you want a true analog take a look at Afghanistan where something like 20-30% of the population may be users. Or Native American reservations where banning alcohol has drastic reductions in crime and domestic abuse rates. Or Singapore that essentially has no junkies.
(Portugal is an example of this approach, generally considered a success)
But Portugal hasn't legalized, taxed anything. (illegal) Recreational drugs are still illegal. There is no need to legalize any drug to do harm reduction. Not even Cannabis is legal in Portugal.
People can be functional heroin addicts (same as functional alcoholics).
Not that it’s a good or desirable thing.
Most heroin overdoses come from cut drugs, or from using at similar level after a break, often caused by prison stints. Both direct consequences of them being illegal.