People turn to drugs because they are addictive. Once you start, it's hard to stop, and it can easily lead to drug abuse. Drug abuse and the lifestyle that it leads to will exacerbate mental illness.
The issue is that the US half-asses its drug enforcement policies. Everything is a leaky sieve full of inefficiency. They have a mostly unprotected border with Mexico, that they're too scared to lock down for political reasons. They have drug dealers that they won't arrest, or put in a revolving door policy, because they're afraid of being called evil by the privileged members of NGOs and academia. Investigating, arresting and putting on trial criminals is extremely expensive and inefficient because there's 50 million legal checks to deal with.
Look at Singapore for an example of how an all-out war against drugs can be effective, and produce a safe society. 98% of the citizens of Singapore support those policies because they have some of the safest streets in the world. Their children can safely be out at any time. Why should they let the criminal 0.5% of the population keep them terrified like in America? It should be the other way around. They get criticized by westerners for their use of the death penalty for drug dealers, such as in this short clip with visionary Singaporean PM Lee Kwan Yew https://www.youtube.com/watch?v=-PXAOZwvv04, who handles it admirably.
The US is violent and dangerous because it tries to give as much freedom as possible to its citizens, and protect their constitutional rights to a high degree, even when this comes at a high expense for the rest of society. I am not saying I want this to change, I like diversity of thought and government, and there's something endearing about how different the average American is compared to other nations. This diversity of thought allows us to learn lessons about the effect of policies and culture. For example this is why I like the USA's 2nd amendment and wish to see it protected, even though I wouldn't want everyone to be armed in my country.