I find the reduction in smoking cigarettes fascinating at a societal level, in a similar way to a few other topics: toxoplasma gondii, widespread use of SSRIs. Probably some others I'm not recalling.

This must have had an effect, beyond health. Surely? It's hard to research because it gets crowded out (understandably) by all the negatives from smoking and all the improvements to health from the reduction of it.

But nicotine does have an effect on the mind. Certainly some positives (concentration, I believe) and I'm sure some negatives too. So the idea that a society would, over the course of a few decades, quite sharply reduce it's use of a particular drug surely must have had some interesting knock-on effects.

I've heard some people wonder if the rise of ADHD diagnoses could be related. That in the past all the ADHD folks would smoke and self-medicate, without even realizing. I have no idea if that's true.