Evo, you may not find shaky people like that around schools but they still exists in large numbers in the sketchy parts of town, any town. You probably don't see them too often these days because you know enough to stay away from those parts of town
moonbear, I meant psychological in the context of having minor long lasting effects.
If you drink a cup of coffee, you feel great and you love coffee, but coffee can be forgotten if you don't have any for a while. Most drugs,
when taken in small amounts, have that mild effect. Things like heroin or nicotine are different in that you'll still crave it long after you've forgotten about it. Some people claim to have that long lasting craving for alcohol, but the vast majority of people do not feel that craving. Normal people like you and I don't suddenly think "oh god, I need some vodka RIGHT NOW!". Amphetamine has that same small minority of people who crave it relentlessly.
Case and point would be how amphetamine is very heavily prescribed by doctors, yet very few of the people on these legal drugs become hopelessly addicted.
A minority of amphetamine users become addicted. A minority of coffee drinkers become addicted. A minority of chocolate eaters become addicted (chocolate contains theobromine). A minority of tea drinkers become addicted (theophylline). One that's shocking is that even cocaine has a low rate of dependency because much of cocaine's world-wide consumption is in the form of coca tea. Contrast that with things that have intense physical addictions. Do you know any casual cigarette smokers? I've known some people who only smoke while drinking alcohol, but most of the smokers I have met in my life smoke regardless of what they are doing. They will leave a comfortable environment and go outside in -40 weather just for the sake of smoking.
The biggest difference between what you can describe and psychological or physical addiction is the ability to be casual with the use of that particular drug.edit: the prices of drugs are often related to how close you are to the supplier. For example, marijuana in BC (Canada) is about $5 per gram. In Alberta it's closer to $10. In Saskatchewan it's closer to $15-20. I think these prices are related to stuff that is grown in BC. For harder things like cocaine, the prices would be expected to drop as you move south because those are from South America. Canada is so far from South America that cocaine simply isn't a problem here because prices are incredibly high; think in the ballpark of $50/gram and up. What really puts the meth epidemic on a new level is that meth is made in Canada and the US using stuff you buy in a store, which of course lowers the price. The lower prices make it much easier to get carried away. Having "too much" cocaine would cost quite a bit of money wheras having too much meth could cost as little as a Big Mac meal at McDonalds. It's scary.
edit2: I bolded and underlined that one part to emphasize it. The human body is very adaptable if you give it small amounts of things that are somewhat bad for you such as drugs, saturated fat, or being outside (sun burn). If you take too much of anything, you can assume it will be bad for you.