Cocaine is a white powder extracted from the South American coca bush. Usually sniffed in lines from a flat surface through a straw but it can also be dissolved in water and injected. Large- scale production made it more widely available. Crack is freebase cocaine, produced in raisin-sized pieces or rocks. (Freebasing is the process by which cocaine hydrochloride is dissolved in water, heated with another reagent to 'free' the cocaine alkaloid base.) Also known as base, rock, or wash, can be burnt on a piece of tinfoil and fumes inhaled, smoked in a water pipe or mixed with tobacco in a cigarette. First newspaper report on crack appeared in the Los Angeles Times in 1984.
Effect: Feeling of well-being, exhilaration, indifference to pain and tiredness, greater alertness. When sniffed, cocaine produces an effect lasting 15-40 minutes. Crack gives instant euphoria which wears off after 15 minutes. High potential for psychological addiction.
Street cost: Cocaine pounds 50 per gram; crack pounds 10 to pounds 25 per rock.
AMPHETAMINE - also known as sulphate, sulph, speed or whizz. Tablets, capsules or powder. Most popular illicit drug after cannabis, revived by Eighties 'rave' culture.
Effect: Synthetic stimulant acts on the central nervous system, causing arousal, increased energy and powers of concentration, sense of well-being. Potential for psychological dependence.
Street cost: pounds 10 per gramme.
CANNABIS - or dope, pot, marijuana, hash (resin), grass, ganja, skunk (herbal). Used rolled up in a cigarette or 'joint' but can be added to food or brewed into a drink. MS, cancer, and Aids patients are campaigning for its reinstatement as a prescribed medicine.
Effect: Mild euphoria, making the user relaxed and uninhibited, but can produce lethargy and depression. Not addictive.
Street cost: pounds 25- pounds 40 per quarter ounce.
LSD - (lysergic acid diethylamide). Impregnanted into small squares of blotting paper and dissolved on the tongue. Used medicinally in the 1950s and 1960s, and tested by the US military and intelligence services. Widely available at raves and clubs.
Effects: A 'trip' causes visual changes with intensified colours, distorted shapes and sizes, movement of stationary objects. Distortion of hearing, changes in sense of time and place. Not addictive.
Street cost: pounds 2.50 to pounds 4 per dose.
ECSTASY - hallucinogenic amphetamine in a class of more than 1,000 chemicals known as MDAs. MDMA (true Ecstasy) is the least common type seized by police.
Effect: Mild euphoric rush followed by feelings of well-being; hallucinations and heightened perception at higher doses. Dancers may suffer heatstroke and dehydration. Not addictive.
Street cost: pounds 10- pounds 20 per tablet or capsule.
HEROIN - an opiate derived from morphine obtained from the opium poppy; fluffy powder, sniffed, smoked or injected. Also known as gear, smack, scag and H. 'Chasing the dragon' involves heating the powder and inhaling fumes through a small tube.
Effect: suppresses emotional activity and makes pain, hunger, discomfort, fear and anxiety tolerable; blood vessel dilation gives a pleasant warm feeling. Can create physical dependence.
Cost: pounds 70- pounds 80 per gram.
BENZODIAZEPINES - tranquillisers, including Librium (chlordiazepoxide); Valium (diazepam); and Normison (temazepam). More than a third of long- term users develop physical dependence. Discovered during a heroin shortage by addicts who injected ground-up pills.
Effect: sedative, but can increase aggression.
Street cost: Prices depend on drug - 50p per temazepam pill; diazepam pounds 1.
THE DRUG-CRAZED American GI is a feature of every Hollywood vision of the Vietnam War but his inclusion is far closer to fact than fiction. By 1971, it was estimated that almost half of all enlisted men had taken opiate drugs, and around 20 per cent of veterans believe they were addicted at some stage.
At the end of the war, the military and medical authorities foresaw a drugs and crime crisis, with thousands of discharged men addicted to drugs which were rare and expensive on Main Street USA. But studies show the majority of the GI 'junkies' were untroubled by their habit and probably never touched illicit substances again. The Vietnam experience has demolished many of the long-held views about what constitutes drug addiction.
Addiction, or dependence, is popularly assumed to be the result of some intrinsic property of the drug itself. Use of some drugs may lead to physical dependence (heroin, benzodiazepines, alcohol) or psychological dependence (cocaine, amphetamines) or a combination of the two.
But Dr Michael Gossop of the Drug Dependence Clinical Research and Treatment Unit at the Maudsley Hospital, London, says addiction cannot be explained in physiological terms - the drug's effect on body cells - alone. Vietnam illustrates the powerful influence of social circumstances on how drug-taking starts, continues - and can be stopped.
The social and moral controls of civilian life were lifted; drugs were plentiful and everyone used them. When they returned home, Dr Gossop says, the absence of these factors explains how a far greater proportion than expected gave them up. Less than 10 per cent used opiate drugs again.
In his book, Living with Drugs, Dr Gossop argues that it is impossible to define addiction or dependence in simple terms. The total effect of drug-taking is an interaction between the drug, the personality and expectations of the user, and the social context in which he or she takes them.
Martin Jarvis, deputy director of the Imperial Cancer Research Fund's Health Behaviour Unit at the Institute of Psychiatry, London, says the 'concept' of addiction is a crutch for many drug-takers who will never try to give up because they are 'addicted'. He cites nicotine, not heroin, as the prime example of an addictive drug. Many researchers maintain that it is as difficult to stop smoking as it is to kick heroin.
However, physiological factors do play a significant role in the development of dependence. For example, nicotine's powerful addictive hold is related to how quickly it is taken into the body. It is rapidly absorbed by the lungs, and is present in the brain within 7 seconds, compared with 14 seconds it takes for the blood from the arm to reach the brain after an intravenous injection. People who take tobacco as snuff are not as dependent as cigarette smokers; likewise people who sniff cocaine are less likely to become dependent than those who smoke it.
The relative addictive powers of illegal drugs are, however, hotly disputed which is why most researchers refuse to give a definitive answer when asked: is cocaine an addictive drug? is heroin withdrawal really to be feared or is it no worse than a bad dose of flu? There are almost as many views as there are researchers.