While low doses of alcohol can be a relaxant and social lubricant, excessive amounts especially over a period of time can be dangerous to drinkers health and safety.

Alcohol reduces the functioning of the limbic system of the brain which is the part of the brain responsible for emotions driving anxiety and fear. So we feel more socially comfortable when we drink.

But the trick is not to drink too much so that our inhibitions are totally lowered, and we begin to put ourselves in possibly dangerous situations.

Because alcohol also affects our cognitive processing, reasoning and judgement, we become more impulsive and much less inhibited.

In higher doses alcohol slows down the rate at which our neurons communicate in the brain, so our heart rate and breathing can be affected. In the event of an alcohol overdose, it is possible for a person to totally stop breathing.

Source: http://www.lifehacker.com.au/2015/12/whats-happening-to-us-when-we-get-drunk/