Alcohol is a rather general term for a class of hydrocarbon compounds, and is widely used as a cleansing agent (for example to wipe the skin before an injection is made). But in everyday talk (and, for the most part, in PSYCHOPHARMACOLOGY) ‘alcohol’ is taken to refer to fermented drinks that contain ethanol (alternatively known as ethyl alcohol). Consumption of these gives rise to a variety of psychological states: alcohol is a PSYCHOACTIVE substance that can act as a SEDATIVE or ANXIOLYTIC, or induce EUPHORIA. Evidence suggests that the practice of producing alcohol for consumption is about 6000 years old, and societies in all places and at all times appear to have discovered means for producing alcoholic drinks. Consumption is world-wide, with the exception, of course, of Moslem countries: the denial of alcohol use appears to represent an example of how humans can consciously and volitionally deny themselves the use of a substance that, when made available to animals, is always accepted. Alcohol is absorbed rapidly by the body and is metabolized, mostly in the liver. There are three stages in its metabolism: ethanol is converted by alcohol dehydrogenase to acetaldehyde; acetaldehyde is quickly converted, by a process involving aldehyde dehydrogenase, to acetic acid (acetate).
Acetate passes out of the liver into the bloodstream. Here it combines with acetyl CoA (acetyl coenzyme A—which is also involved in the synthesis of acetylcholine) and is finally broken down to produce carbon dioxide, water and to produce 7 calories per gram of alcohol. Excessive alcohol intake very rapidly induces body weight gain, amongst a raft of adverse effects on the brain, heart and on behaviour (see ALCOHOLISM) and as with any other addictive agent (see ADDICTION; SUBSTANCE ABUSE), TOLERANCE can develop and absence provoke WITHDRAWAL SYMPTOMS. Low to moderate doses can have benefit; higher doses unambiguously do not.
The effects of alcohol on the brain are not especially well understood. It appears to have a generalized effect on neuronal membranes, interfering with the lipids in the membranes themselves, as well as affecting ION CHANNEL activity. Alcohol has also been associated with changes in the function of a variety of neurotransmitter systems, including GABA, DOPAMINE, acetylcholine, SEROTONIN, NORADRENALINE and OPIOID PEPTIDE systems.
