[aruanan]

For example, there are unknown components in the tobacco smoke which inhibit MAO B enzyme, the enzyme which breaks down dopamine

There are compounds in broccoli that appear to do the same thing. On another note, I just attended a post-doc's presentation about certain mutations that can lead to the failure to break down dopamine, leading to endogenous dopamine toxicity, so it looks as though you can get screwed either way.

[LifeOrGoods?]

endogenous dopamine toxicity

What the hell is that and why does it sound so damn scary?

[nightlight7]

...certain mutations that can lead to the failure to break down dopamine, leading to endogenous dopamine toxicity...

There is also "water toxicity" i.e. you can die if you drink too much of it. In the case of MAO B inhibition and other dopaminergic effects of tobacco smoke, the ancient 'gift of gods' seems to have been well tuned over the millenia of cultivation and life-long use by billions of test subjects, to maintain the optimum youthful levels of MAO B and dopamine (also of acetylcholine, glutathione, catalase, SOD, pregnenolone, DHEA, testosterone,... see the links given earlier). Tobacco smoke is the closest thing to youth elixir humans have ever known.