Alcohol (ethanol) is man's favorite recreational drug and the psychoactive substance most often encountered in forensic toxicology casework; impaired driving cases, sexual assaults, and drug intoxication deaths. Because of the legal consequences of a person's blood- or breath-alcohol concentration (BAC or BrAC), the analytical methods used must be accurate, precise, and fit for purpose. The gold standard method for determination of ethanol in blood and other biological specimens is gas-liquid chromatography with flame ionization detector, although some laboratories also use a mass spectrometric detector. Also widely used for legal purposes are breath- alcohol analyzers; at the roadside as screening tests and also as evidence for prosecution of traffic offenders. Evidential instruments determine ethanol in exhaled breath by infrared spectrometry at wavelengths of 3.4 and/or 9.5 mu m or by electrochemical oxidation with a fuel-cell detector. The impairment of body functions after drinking alcohol depend on the amount consumed (the dose), the speed of drinking and the BAC reaching the brain. After drinking 1-2 units of alcohol (similar to 16 g ethanol) people become more talkative and feel less inhibited (BAC <50 mg%). Cognitive and psychomotor functions are impaired as BAC reaches 80 mg% and at 150 mg% the signs and symptoms of alcohol intoxication are much more obvious including slurred speech, lack of coordination, confusion, and combativeness. On reaching BACs of 300-400 mg% most people are incapacitated and/or unconscious with slow and shallow breathing and at risk of death from paralysis of respiratory centers in the brain stem. This article is categorized under: Toxicology > Alcohol Toxicology > Analytical Toxicology Toxicology > Drug-Impaired Driving