Im not sure if people are genetically predisposed, but they are predisposed for many reasons! Environment, social acceptence, family bad habits, and nutritional deficiencies! Example, a vitamin D deficiency in mothers is known to cause Schizophrenia in the child, which in its self is cause to become addicted to drugs and alcohol!
Subascorbemia, a vitamin C deficiency, plays a big part in addiction as it makes the amino acids responsible for properly processing alcohol to a non toxic substance!
There is nothing you can do about a genetic predisposition but you can control nutritional deficiencies!

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When I say genetically predisposed to addiction, I mean more than to just drug/alcohal addiction. I think that some people just can NOT do things that they like in moderation. These can be good or bad things. For example, if I like something, I over do it...I will find a new food I like...right now it is home made tomato soup...so ALL I eat is tomato soup! I will do this for a while until I am sick of it, and don't ever want to eat it again. I do this with most foods. I think that people can be addicted to religion, work, exercising, etc. I find that I do this with just about everything in my life. When I was a gymnast, I was at the gym ALL the time; when I get in the mood/need to shop for clothes I will buy a lot of stuff each time I go to a store and will go many times. I am compulsive with keeping my house clean; and even when I decided to get clean from drugs and enter rehab I went overboard with that...I went to a LOT of meetings, and was consumed with being clean.

I am made up of many things. I am part Polish, Irish, German/Belgium, and English. My families history with addiction can actually be traced back to the early 1800's or late 1700's. It's actually a funny story. My grandfather started doing our family tree, and traced it back quite a long way...and then all of a sudden he just STOPPED! We later found out that he stopped his search when he found out that we are related to a DUKE! The only problem is that this duke was a drunk...this distant relative was quite the character, and got himself into lots of trouble, and I believe eventually was either shunned or stripped of his title...I can't remember exactly.

I guess I have those 'drinking' genes from the both the Duke and from being Irish; like you said. BUT I don't like drinking! I don't know why; it's just not something I was ever fond of. I was never into pot either...however almost all of my relatives are/were. I guess I just found the drugs I liked and over did those!!! I wish I had liked pot instead of heroin!