Hey, I'm just gonna throw this out there because I SHOULD be studying for my grad school human osteology quiz but instead I'm reading NS ignorance. /claim (I think saying you're in grad school is a claim, although I'm not sure I want to admit that I still show up on NS when I'm in grad school)
Major study was done on genetics and brain chemistry involving addiction to alcohol. You are born with genes in which you get half from your mother, and half from your father (you with me so far? Don't fall off the train...). In regards to alcohol addiction, you have a pair, known as long long, long short, and short short (yes there is a huge complicated name but I'm keeping it simple). If you have a long gene from your father and a long gene from your mother, you are 30% LIKELY to develop an addiction to alcohol NO MATTER HOW MUCH YOU DRINK. Short gene and a long gene, 50% chance of developing an addiction to alcohol (again, no matter how much you drink), but then it goes up huge if you have a short gene and a short gene, you now become 80% likely to become and alcoholic no matter how much you drink, so I do believe that it has a little more to do with genetics and inheritance than has been previously stated in this thread.
Now for some interesting facts about smoking pot: when you smoke in excess for long periods of time, is has been understood to decrease the amount of serotonin output in the brain, causing you to become addicted to marijuana SLOWLY. I'm not saying that if you smoke once or twice or even every day for a week, you're going to be addicted, BUT I am saying that if you habitually smoke pot over long periods of time, you will develop an addiction because your brain becomes accustomed to that change in its chemistry. That's why if you habitually smoke pot you are cranky/jittery/moody/etc when you stop smoking for a while because your brain is re-learning how to produce certain chemicals on its own. Oh, and yes, smoking pot habitually does cause cancer of the lungs.
Having one drink for women and two men of alcohol every day for the rest of your life CAN reduce the risk of heart disease and stroke though, and smoking marijuana can help some people with asthma, general nervousness/paranoia, and GREATLY reduces the pain in cases of patients with cancer and I can tell you it's also highly effective with migraines/upset stomachs as well.
Just remember, it's all about the quantity in which you use these things, and YES, genetics does play a HUGE role in alcoholism and probably drug addiction. So if alcoholism runs in your family (as it does mine) or drug addiction (again, as it does in mine) then you're best to drink/smoke in moderation.
That is all.