Weed, grass, ganja, skunk or sinsemilla refer to marijuana (the dried plant). When cannabis is ground and pressed into blocks of resin, it is called hashish and is sometimes known by its colour and country of origin, as in black Moroccan or red Lebanese. Much less common, and strongest of all, is cannabis oil.
Specialist indoor growing techniques (hydroponics) have led to the cultivation of strong varieties which can have hallucinatory effects. Cannabis plants are also cultivated - legally and under licence - for the production of hemp, once an important crop, which is nowadays used in cosmetics and to make rope, paper and cloth.
What does it do?
Cannabis is a depressant and a sedative, so it slows down brain functions. Its psychoactive ingredients are called tetrahydrocannabinols (THC), the compounds responsible for the feeling of being "stoned". The immediate physical effects of THCs on the body are an increased pulse, decreased blood pressure, bloodshot eyes and increased appetite. Being stoned can make the user feel giggly and talkative, or drowsy and subdued, depending on the dose, the person's mood and the surroundings.
Short-term memory and co-ordination deteriorate, while prolonged or heavy use can adversely affect people with mental health problems, and reduce concentration and motivation. Some users report a heightened awareness of sounds or colours. The effects on concentration and motivation make learning, or teaching someone under the influence of the drug, much more difficult.
Cannabis is usually smoked mixed with tobacco, with all the harmful effects that can have. But there is no evidence that by itself cannabis is physically addictive, although it can lead to a psychological dependence.
When eaten rather than smoked, cannabis takes longer to enter the bloodstream, but has a stronger and more unpredictable effect. It is impossible to overdose on cannabis, although consuming large amounts can sometimes lead to panic attacks and paranoia.
A potted history
The cannabis plant has been cultivated for its medicinal and physical properties over thousands of years and, until prohibition in the 20th century, was commonly grown and widely prescribed. First mentioned 5,000 years ago in a Chinese compendium of medicines, it was praised by Emperor Nero's surgeon, Dioscorides, for its therapeutic properties, and exported to the New World by Spanish sailors and North American settlers.
Hemp was once an important crop and the main raw material for making paper, sails and rope. The medicinal use of cannabis in the UK began in the 1840s after a doctor, W B O'Shaughnessy, brought it back from India and hailed it as "an anti-convulsive remedy of the greatest value". Queen Victoria's doctor recommended it as a "valuable therapeutic agent" and, at the beginning of the 20th century, it was commonly prescribed in a variety of herbal preparations and tinctures.
Its medical use was prohibited in 1928 after a conference on narcotics in 1924 at which an Egyptian doctor claimed that with habitual use "the countenance of the addict becomes gloomy, his eye is wild, and the expression of his face is stupid... his intellectual faculties gradually weaken and the whole organism decays".
The first arrest in this country for possession was in a Soho jazz club in 1952. It went on to become the drug of choice for hippies in the 1960s, and during the reggae boom of the 1970s - smoking "herb" is a central practice of the Rastafarian faith - its popularity spread. As general drug consumption increased throughout the 1980s and 1990s, it became widely available.
So what's the score now?
Cannabis was banned outright under the 1971 Misuse of Drugs Act, which classified it as a class B drug. It is illegal to grow, possess or supply cannabis, and it is an offence to allow your house to be used for growing or smoking the drug. But following a report from the Advisory Council on the Misuse of Drugs, published earlier this year, Home Secretary David Blunkett this week reclassified cannabis as a class C drug. The maximum sentence for possession will be reduced from five to two years - although the maximum sentence for dealing has doubled from five to 10 years. Police will still be entitled to arrest for cannabis use, particularly if there are aggravating factors, such as smoking cannabis in front of minors, or when at work. In 1999, 97,000 arrests - 74 per cent of all drug arrests - were for cannabis-related offences.
Police attitudes to possession vary considerably between forces but the issuing of cautions for possession of small amounts is becoming more common. A year-long experimental scheme in Lambeth, south London, has treated possession for personal use as a non-arrestable offence, allowing police to concentrate resources on fighting harder drugs. The scheme has been extended after showing considerable savings on police time, and a 50 per cent reduction in street crime. But local opinion is divided, with some people saying it has attracted more dealers to the area and is giving out the message to young people that it is OK to smoke cannabis. Brian Paddick, Lambeth's commanding officer, was suspended from duty in March pending an inquiry into allegations by an ex-partner that he had smoked the drug.
Disciplinary procedures at schools in the borough have been unaffected; as a spokesman for Lambeth local education authority points out, possession of cannabis is still against the law.
Who's doing it?
Everyone from princes to pop stars. When even Prince Harry and the boys from squeaky clean teen band S Club Seven get caught smoking a sneaky joint, it shows that cannabis use has become a mainstream activity - or, as Noel Gallagher of Oasis once remarked, as normal as having a cup of tea.
The estimated three million regular users in the UK are of all ages. According to the drug advice agency DrugScope, 2 to 3 per cent of 11 to 12-year-olds are estimated to have taken an illegal drug, rising to 23 per cent of 14 to 15-year-olds. Forty-four per cent of 16 to 19-year-old boys have tried an illegal drug, cannabis being by far the most common. A study by the former Standing Conference on Drug Abuse - now part of DrugScope - found that drug use among 15-year-olds increased eight-fold during the 1990s. Wider availability of drugs in general and the rise of dance culture in particular (with its associated use of ecstasy, which has fallen in price considerably in the past decade) could explain the increase.
How can you tell if someone is using cannabis?
The most obvious sign of cannabis use is its distinctive, pungent, bittersweet smell. A user who has recently smoked may have bloodshot eyes, a dazed expression and an inability to concentrate. Finding paraphernalia associated with making joints, such as the butts and paper from cigarettes that have been stripped of tobacco, torn Rizla packets or discarded "roaches" - the rolled-up cardboard filters used in joints - may indicate that cannabis has been smoked on school premises.
And what should you do?
Viv Evans, head of drug education and prevention at DrugScope, says schools must develop a drug policy in consultation with agencies, local police, governors and possibly parents and pupils. This should spell out the sanctions available to the school in the event that pupils are found using or possessing drugs, but should also stress the welfare of the young person.
"This needs to be communicated to the pupils so they know what is tolerated and what isn't, and the help and support they will get if they have a problem," says Ms Evans. But not all schools have drugs policies in place. In September 2000, Ofsted reported that 75 per cent of primaries and 93 per cent of secondaries had drugs education policies but only 42 per cent and 95 per cent respectively had any policy for dealing with drug-related incidents. Only one in six primary schools and one in three secondaries involve pupils in putting these policies together. The DfES model drugs policy for schools states that "possession and use of drugs in school or during the school day is inappropriate... these rules apply to adults working at and for the schools".
It says the headteacher should inform the parents of anyone found in possession of drugs "at the earliest opportunity" so "the school and parents can then work together to support the young person". There is no legal obligation to inform the police, although they can help in testing or identifying suspect substances. Use of drugs off school premises should be dealt with at the "teacher's discretion", according to the advice.
But Viv Evans says that if teachers notice a marked decline in a pupil's performance or a change in behaviour, and suspect cannabis use is the reason, "they don't have to try to sort it out by becoming social workers but they need to be aware of the referral agencies and allow the student access to drug advice".
She adds: "Schools need to be aware of young people's drug use. It's important to distinguish between recreational use and experimental use. I don't believe they should take a punitive approach, but you have to bear in mind that using drugs can affect young people's achievement and performance."
The Department for Education and Skills advises that permanent exclusion should be a "final sanction when all other reasonable steps have been taken". There are no definitive figures on the proportion of the 8,600 pupils permanently excluded from school in 1999-2000 for drug offences, and schools are understandably reticent to publicise them. Anecdotal evidence and localised studies suggest that the proportion excluded for drug possession or supply is probably less than 5 per cent. One anonymous survey of north London local education authorities showed that drugs were the reason for 3 per cent of exclusions. While exclusion has been used by some (mostly independent) schools as a means of stamping out drug use, it is not a successful strategy for helping young people kick a drug habit. Being kicked out of school greatly increases the likelihood of their getting involved with drugs; 63 per cent of excluded children had been offered cannabis compared with 25 per cent of those still in school, according to DrugScope.
Some independent schools have introduced testing - usually on a sample of hair - to discourage and identify drug use. But drug advice agencies criticise blanket testing because it does not discriminate between the occasional user and someone with a serious problem, as traces of cannabis stay in the body for several weeks after use. "It promotes a culture of suspicion in the school which is counterproductive to good drug education," says Ms Evans.
A gateway drug?
Rosie Brocklehurst of Addaction, the UK's main drug treatment charity, says there is no evidence that cannabis leads to harder drug use. Because of its position at the "soft" end of illegal drugs, it is often mistakenly seen as leading inevitably to heroin and cocaine, and its use is viewed by some with horror. But, says Ms Brocklehurst, "a hysterical reaction doesn't help anybody - least of all the child".
Teachers would do best to treat the child sympathetically, she says, identifying how regularly they are using cannabis, whether they are taking any other drugs and whether it is symptomatic of a problem. Then, with their parent or carer and headteacher, they need to find ways of addressing their use. Above all, she says, "every case must be treated according to the individual".
Did you know?
* The cannabis plant was first mentioned 5,000 years ago in a Chinese compendium of medicines and was commonly prescribed in herbal remedies before its medical use was prohibited in 1928
* Forty-four per cent of 16 to 19-year-old boys have tried an illegal drug, usually cannabis, says the charity DrugScope
* In 1999, 74 per cent of all drug arrests - 97,000 people - were for cannabis-related offences
* Cannabis plants are cultivated legally for the production of hemp, which is used in cosmetics and to make rope, paper and cloth
Case study: school daze
"You smoke spliff Sir, we've seen you!" a pupil once shouted as he ran past me in the corridor. A colleague cleared up my confusion; the pupil had seen me smoking a menthol cigarette. He'd automatically assumed that my all-white cigarette was a joint - and he was determined to tell anyone who would listen.
I found him, took him to one side, showed him my cigarettes and did the "I wish I didn't smoke" speech, knowing full well he was on 10 a day. The thing that struck me most was how disappointed he looked that I was not smoking spliff in school.
Cannabis has taken over in street cred terms where cigarettes were once king. How many of us have taken a glimpse at the graffiti in the back of an exercise book and found a picture of a joint or a cannabis leaf? It is glorified, mythologised and increasingly used by our pupils - and therefore an issue that we have to deal with.
I once spotted two pupils behaving in a bizarre manner at the bottom of the playing field. When their head of year and I apprehended them, they were in a particularly giggly state, so we asked them if they'd taken anything. They confessed arrogantly to being stoned and handed over a block of resin. It didn't look right to me so I sniffed it. "Aaahhhhh... Bisto." They'd been sold and were happily smoking a stock cube. Convinced it was the real thing, they were behaving accordingly. Like so many other drugs, the effects are as much in the mind as in any biological reaction. They soon sobered up when I told them they'd been smoking gravy.
I've been convinced several times that a pupil has been high, only to be told I'm wrong by the managers I've referred the matter to. After one such incident, I asked a manager whether he'd ever smoked cannabis himself, or whether he had seen someone smoke it, or even knew what it smelt like. He answered no to each of these questions, but still insisted that the dazed pupil outside had not taken anything.
I have never yet caught a pupil "in the act". What would I do if I did? I'd have to confiscate the drug and inform the management team. According to school policy, the pupil would then be subject to a short-term exclusion and, if found to be dealing, he or she would be permanently excluded. In spite of all the debates and moral arguments, the use of cannabis is an illegal act and has to be dealt with accordingly. But the policy in my school - and several others - doesn't tell me what to do when the pupil returns from their exclusion. Smoking behind the bike sheds has changed, and so must our responses to it.
We must keep this issue in perspective. When we think about drug use among our pupils, we tend to worry most about harder drugs. But we need to remember that in all schools the most widely used and abused drugs are nicotine and alcohol. This has been going on for centuries, yet we seem no closer to educating our pupils not to use them, or to finding out how to eradicate them from schools. So why assume we are going to be any more successful with cannabis?
The writer teaches in the Midlands.
* www.ofsted.gov.ukpublic docs00drugsed.pdf. Ofsted update on drugs education in schools.
* www.drugs.gov.uk. Interdepartmental government website on national drug strategy. l www.isdd.co.ukdrugsearchindex.html. Very informative guide to drug use of all kinds.
* www.thesite.org.uk infodrugs. Teenagers' site with info on the law in other countries.
* www.transform-drugs.org.uk. Leading independent drug charity with research, help and advice.
* www.ndh.org.uk. The National Drugs Helpline publishes leaflets for teachers and parents. It has an advice line: 0800 77 66 00.
* Narcotics Anonymous (www.ukna.org), 202 City Road, London EC1V 2PH. Tel: 020 7251 4007. Helpline: 020 7730 0009.
* Lifebytes (www.lifebytes. gov.uk). Covers a range of personal and social issues, including drugs. Colourful and accessible. Requires Flash plug-in. Suitable for KS3.
* The BBC site www.bbc.co.ukeducationid gives an objective view of the drugs young people are likely to come across. Includes a discussion board and "Who to contact", a useful list of support groups. KS34.
* The NHS site www.trashed.co.uk allows users to search for a specific drug to find out about its origins, effects, the law, what do to in an emergency and the risks.
* The Boots site www.bootlearningstore.comks3drugs provides a useful overview.
* The government site www.mindbodysoul.gov.ukdrugsdrugmenu.htm is similar to Lifebytes (see above) but is more suitable for KS4 pupils.
* All About Drink and Drug Abuse, by Alexander McCall Smith (Macmillan Education, pound;5.75). Discusses drink and drug abuse and the likely short and long-term effects. For secondary pupils.
* Drug education for children aged four to 11, by Janice Slough (Daniels, pound;4.99); Drug education for children aged 11 to 16, by Janice Slough (Daniels, pound;7).
* Face The Facts: drugs, by Adrian King (Hodder Wayland, pound;9.99). Geared towards young people with learning difficulties, this book describes drugs - from alcohol and cigarettes to heroin and paracetamol - and why people take them.
* Drugs, by Bridget Lawless (Heinemann, pound;3.50). Designed to motivate secondary school students with a reading age of eight to nine.
* Drugs, by Anita Naik (Hodder, pound;3.99). An informative guide which covers drugs and peer pressure, the law and drugs, alcohol, smoking, "hard" and "soft" drugs, their descriptions, effects, the myths and realities.
* Learn to say no: cannabis, by Angela Royston (Heinemann, pound;9.99). For primary children.
* Poems with Attitude, by Andrew Fusek Peters and Polly Peters (Hodder Wayland, pound;4.99). Straight-talking poems that capture the uncertainties and pressures of being in your teens. Includes poems on domestic violence, drug abuse, sex, bullying and joy-riding.
* What about health: drugs, by Fiona Waters (Hodder Wayland, pound;9.99). This book looks at what drugs are, how they are used in sport and how medicines help you when you are ill. Differentiated text titles allow pupils with lower reading abilities to enjoy the same topics as their classmates.
* What do we think about drugs?, by Karen Bryant-Mole (Hodder Wayland, pound;9.99; pound;5.99, pbk). Aimed at children who might be introduced to drugs at school and in daily situations at a young age.
* The Courage To Say No, by Kwasi Koranteng (Macmillan, pound;3.99). Can Asebu find the courage to say "no" to drugs? Reading age: 12-16.
* Does This School Have Capital Punishment?, by Nat Hentoff (Heinemann pound;5.99). The innocently disruptive, absent-minded Sam attracts trouble, and when caught with cannabis in his hand he's hard-pressed to prove his innocence and avoid expulsion.
* Falling Awake, by Vivian French (Barrington Stoke, pound;4.50). Danny enjoys making easy money out of the younger kids, but his world is turned upside down when he tries his wares. Reading age: 8-12.
A full list of resources on cannabis is available at www.tes.co.uk. Additional resources research by Reach, the National Advice Centre for Children with Reading Difficulties. Its information helpline is 0845 6040414
Additional research - Tracey Thomas.