You need strong communities and a culture that rejects most if not all forms of illegal substance use and views them as a negative (alongside legal unhealthy habits) to really save the young and vulnerable from falling into these pitfalls.
Clamping down on the source certainly helps, but if the culture is failing and the communities aren't strong enough then the issue of mis-use remains and can only be managed to a certain degree with the resources and policies available.
Certain cultures do still breed that collective community rejection of drug usage and that has to be a big part of why these groups don't suffer to these ills.
You either go zero tolerance (Taiwan, Singapore, South Korea, Japan etc..) and the community and culture as a whole picks up the slack and acts as a buffer against the small minority of illegal substance mis-use that exists, or you liberalise the entire thing further and then pump billions more into the system each year and tackle the issue through money, a damage mitigation strategy.
On an anecdotal level, even with weed, the stoners in my circles that have smoked through their 20s, 30s and into their early 40s, aren't able to maintain a stable job, are unemployed, have other substance issues that have spiralled out of control and have emotional instability and early signs of psychosis and disconnect with reality. Those that have smoked up from their teens into their 20s have suffered from mental health issues.
So, I personally believe zero tolerance is the best approach, because many of those advocating liberalising drugs even further in the west rarely explore the cultural implications of doing so. They always focus solely on crime. But, there will surely be many consequences to the individual and therefore the culture a whole.
