Alcohol is a central nervous system depressant. It is an ethanol produced by the action of yeast on sugars. Ethanol is a biphasic drug: low doses have a different effect to high doses.
Small amounts of alcohol (one or two drinks) act as a stimulant, reducing inhibition and producing feelings of mild euphoria. Higher doses depress the central nervous system, initially producing relaxation but then leading to drunkenness - characterised by poor coordination, memory loss, cognitive impairment and blurred vision. Very high doses cause vomiting, coma and death through respiratory failure. The fatal dose varies but is somewhere around 500 milligrams of ethanol per 100 millilitres of blood.