Like many other poisons, small amounts of alcohol can be tolerated by the body - in fact, there is evidence that small amounts of alcohol can protect against certain illnesses, such as heart disease. But there is much more evidence to show that excessive drinking puts a person's long-term health at risk, and the more he or she drinks, the greater the risk becomes.
The immediate effect of drinking alcohol - a feeling of elation or relaxation - is because it has a depressant effect on the brain and central nervous system. It results in a dulling or slowing of a person's reaction times, thoughts and co-ordination.
Long-term heavy drinking can have a far more serious impact on a person's mental state, in extreme cases even causing irreparable brain damage. Heavy drinking is closely linked with mental illness. Alcohol is known to cause anxiety and depression, which may accelerate or uncover an underlying predisposition to a psychiatric disorder. Two-thirds of suicides have been linked with drinking.
But the organ that bears the brunt of long-term drinking is the liver. Although the liver has a powerful ability to regenerate itself, excess alcohol can slowly destroy this vital organ. If the liver has to break down too much alcohol over a long period, its other functions become impaired and the organ becomes damaged. Excess alcohol results in a progressive deterioration of the liver, causing fatty liver, hepatitis and cirrhosis which can lead to total liver failure and death.
Other digestive organs are also affected by alcohol, for example, the pancreas. About 400 people a year die from alcohol-related pancreatitis.
The lining of the stomach wall is also irritated by alcohol which can result in gastritis, symptoms of which range from nausea, cramps and fever to heartburn, weight loss and vomiting. Some sufferers develop stomach ulcers or even stomach cancer.
Throat cancers are also higher among heavy drinkers. In fact between a quarter and a half of all head and neck cancers are due to excessive drinking, according to Alcohol Concern.
Although regular but small amounts of alcohol can lower the risk of heart problems for people over a certain age, heavy drinking has been linked with high blood pressure, chronic heart disease and stroke.
Alcohol Concern says binge drinking, especially in young people who are not used to alcohol, can cause irregular heartbeats, palpitations and in rare cases, sudden death - sometimes called "holiday heart" syndrome.
Osteoporosis - brittle bones - is associated with post-menopausal women but there is evidence that both men and women in their twenties who drink heavily are at higher risk of developing the condition. A recent study has shown that about half of those who misuse alcohol on a regular basis show signs of osteoporosis, which makes the bone soft and liable to collapse, especially in the lower spine, pelvis and thigh.
Scientists have also linked muscle degeneration with heavy drinking and skin complaints are common among alcoholics.
Over long periods, alcohol can cause sexual problems and infertility. Drinking can cause temporary impotence as well as lowering sperm counts in men. In women, excessive alcohol can result in a failure to ovulate.
Drinking during pregnancy can affect the development of the foetus, which can result in low birth weight or more severe malformations for mothers who are very heavy drinkers.