Regarding the relaxing effects of the stimulant Nicotine (If nicotine is a stimulant, why does it seem to calm people? - The Straight Dope), I just wanted to mention a short film I saw about 30 years ago in JHS about cigarettes. The film interviewed several smokers, with each one mentioning that smoking helped to calm their nerves. At the time each person was interviewed, they had not had a smoke, and all were feeling “jittery”.
Each smoker was then asked to hold a small metal probe, and try to put the tip into a small hole on a tabletop machine. A counter would click if the probe touched the sides of the hole (think “Operation!”). I don’t recall the actual “scores” (maybe one or two clicks per second, over about 10 seconds), but the point was that after each smoker was given a cigarette, and presumably felt calmer, they re-took the test, and it was clear that each smoker’s hand was much more jittery, as the “scores” shot up like a pinball counter. Maybe it was just propaganda and selective editing, but the idea (Nicotine calms the mind, not he body) has stuck with me ever since. Not that it kept me from wanting to smoke… the crappy taste and the feeling of being kicked in the lungs did that.