Yeah, this is not the best question because you’ll get very different answers from different parts of the world, or even different parts of the US.
I graduated more than a decade ago, and there was a lot more nuance than what you described. They taught us about different types of drugs and what their real effects were. I remember learning in high school that marijuana is less dangerous than cigarettes and alcohol.
In elementary school for me, there were big anti-smoking campaigns, but nothing about alcohol or harder drugs. The “just say no” was about peer pressure and doing anything you felt uncomfortable doing (including inappropriate touching).