How fast does it take for alcohol to effect you?

It takes about 20 minutes for the effect alcohol to be noticeable. But Eating food whilst drinking will slow down the absorption rate. For every 2 or 3 drinks you should have a glass of water. (this will also slow down absorption rate.) Sometimes people will have a greater resistance to alcohol i.e.

Someone being way over the driving limit but not be affected at all by the alcohol.

I think the more appropriate question would have been; What factors affect alcohol absorption.