Greeks tend to drink on social occasions and you will rarely witness scenes of extreme drunkenness in the streets or in bars, clubs etc. Alcohol is freely available 24 hours a day even from kiosks in the streets.
The common beer brands dominating the market are anything but local: Amstel and Heineken boast a combined market share of around 70%. However, over the last few years many new Greek brands have been introduced into the market and are steadily gaining in popularity: Mythos, Alpha and…Fix (named after a Bavarian brewer of the early 20th century) are a few among these. Most other well-known international brands are widely available.
Go easy on beer as most brands have an alcohol content of five percent or higher.
Greeks generally drink beer in the summer months and usually as an accompaniment to their meals.
Stick to beer or wine unless you are absolutely certain of the quality of the spirits served. Some bar owners serve cheap (methanol-based) spirit substitutes out of branded bottles and a great night out may end up in a miserable day in bed nursing a nasty hangover.
Is this practice illegal? Well, it sure is, but, then again, you are not in Switzerland and some Greeks will always discover new and resourceful ways to break the law if they can make a good buck out of it.
A visitor should not leave Athens without savouring Ouzo, the renowned traditional spirit (together with scotch, to be sure) that is best enjoyed with seafood meals. Diluted with water and ice, it becomes a lovely milky-coloured aniseed-flavoured drink, but be warned: it will give you the worst hangover of your life if you consume it in excess. 
Masticha is another pleasant, sweet-tasting spirit, made with the resin of the Mastic tree and is an exclusive product of Chios island.
Greece produces a plethora of international and local grape varieties, which make very good wines. Retsina is of course the most famous of these, with a pine resin flavour, which is added during fermentation. It is, however, looked down upon by modern-day Athenians, who don’t think of it as classy enough for their refined taste buds: more of a peasant or working class wine.