Alcohol is a drug, which slows down the brain, therefore it is a depressant. Alchohol is taken very differently in different countries and societies - in some, drinking alcoholic drinks is a very common activity, whereas in other places, it is banned.
Alcohol slows down reflex actions because it reduces the rate at which neurones conduct nerve impulses. Therefore, in a situation where thinking clearly and quickly are important, drinking alcohol beforehand can be very dangerous. This is why there is the drink-drive law - as many accidents are caused when the car driver had drunk alcohol.