I am not an intellectual nor from the academia. I deal strictly with my experience and history as I have tried to understand it. Having a clear knowledge of every molecule of alcohol will not tell me what it will do to MY brain. I can watch some drink with total responsibility and others with total irresponsibility and what does that tell me? I cannot testify about substances from the poppy fields, coco leaves or marijuana. Other people with some knowledge of these substances say the same conditions apply.
On the other hand, I do not believe I have ever seen a non-addicted person use tobacco more than once or twice.