Why do people vomit after they've drunk alcohol?

Alcohol is a toxin. In small amounts, the toxin can create a mellowed or buzzed feel. When consumed in large amounts, alcohol poisoning may occur. If the alcohol poisoning is severe, it can actually be fatal. Your body is able to recognize when you are going over your safe limits, and will send triggers to your brain to start getting cleared out. One of the ways it does this is vomit. It will try to get rid of any that you consumed before it is absorbed, although by the time you get to this point, you have already absorbed a good bit.

Throwing up from drinking does not automatically mean a severe alcohol poisoning. It could just mean that your body has a lower trigger point. However, it can be a symptom. If there is vomiting along with cold skin, bluish skin tint, seizures, jerky or irregular breathing, passing out, or irregular heartbeat it is time to get some help.