Answer:
Alcohol affects different people in different ways. A child could die from drinking a few shots, while for others it's child play. Tolerance also plays a role, if you drink a lot of alcohol your body gets used to the poison and has a better job of clearing it from the bloodstream. Hence, the reason why some people don't get as intoxicated as others.
And fact is, any amount of alcohol can harm the brain, there is no such thing as a "safe" drinking amount.
So my answer to your question is, any amount.