Using chemicals to alter the way the mind processes information and sees things has been going on throughout history. A young person's use of a drug such as tobacco, alcohol, cannabis or heroin usually starts through a desire to experiment, looking for 'kicks' - often fuelled by what mates or contacts encourage, even though the risks are clear. Use can become uncontrolled and becomes dangerous and eventually life-threatening when it takes over lives.

Drugs are classified broadly into different categories. The drugs that seem to be the most dangerous are given an 'A' classification. Drugs so far assumed to be less dangerous are given a lower classification (class C) and whilst there are still dangers in using these drugs the penalties for possession and supply are accordingly lessened, as shown:

Sometimes the addiction to a drug or drugs is strong and even when the use of drugs leads to serious physical and mental problems, a person using drugs may still not wish to or have the will to stop. If they do decide to give up, they may then find it's extremely hard, especially if they are in contact with other young people who use drugs. The reason for taking drugs is different for each individual:

Social or personal issues can be factors leading to drug dependency. However, the major issue is peer pressure. So there needs to be openness about the difficulties and suggestions to build a confidence to avoid this kind of peer pressure to conform. Young people need to feel strong enough to make their own decisions, whatever friends might be encouraging. It may be helpful for an individual and their contacts to be clear about the effects of different drugs - how they affect the brain and other body functions in the short and long term.

Dreamer?
Cannabis, marijuana and hashish contain a chemical called THC, which acts on neurons in the brain especially those associated with perception, movement and memory.

Raver?
Ecstasy, the popular dancing drug may make you feel fantastic at a party or club but it kills neurons and affects the levels of dopamine and seratonin in the brain. Brain scans show that it causes damage to the frontal lobes and hippocampus, areas that are vital to memory and learning. The heavier the use the more damage there is.

Daydream or nightmare?
Hallucinogenic drugs like LSD (acid) lead to a dreamlike state with heightened awareness of the senses and flashbacks. Perceptions are mixed so that sounds can invoke images and images can invoke smells. Chemically, LSD is very similar to the brain chemical seratonin. As LSD disturbs the brain's normal functioning, its use can lead to 'bad trips' where people experience nightmares which appear to them to be real and can be extremely frightening.

Waking up?
Stimulants like cocaine ('coke') reduce the brain's ability to remove chemical messengers after they have done their job. This gives a quick 'high' with sometimes dangerous increases in confidence, euphoria and energy which are then followed by depression which can only be relieved by more using more of the drug. This loop leads to a powerful addiction. Brain scans show that neurons in many parts of the brains of coke addicts do not use glucose, their energy source, effectively.

False happiness?
Heroin and Morphine result in a sudden increase in Dopamine in the mid brain's 'pleasure centres' and affect the normal working of Endorphin. These drugs are particularly dangerous as they seem to deactivate areas of the brain including those which measure and respond to pain. Withdrawal effects are very severe as they are associated with the production of a variety of stress hormones.

What are the symptoms?

Each drug has different patterns of use and intoxication. For each different drug, the term 'drug use' can cover different levels of use, including: experimenting a little, bingeing, using large amounts without appearing intoxicated and using large amounts to get intoxicated or 'high'. You might be worried that a friend is becoming hooked on a drug or be a concerned parent or guardian. There are some clear symptoms to drug use although some behaviour that might seem to be drug related can occur fairly naturally.

The symptoms listed here may not affect everyone in the same ways. They depend on the amount taken as well as the time. Worried parents often want to know the tell-tale signs of drug use, but the simple answer is that it's not always easy to recognise. Many drug users conceal their use from health professionals, so it's obviously not easy to identify. Mental symptoms can include:
. anxiety
. depression
. disrupted sleep and rest
. large and rapid mood swings
. a need to relearn coping strategies
. reduced wellbeing and health

Other symptoms, linked to specific drugs, might include:
Alertness and hyper activity [amphetamine]
Bloodshot eyes [marijuana]
Confused, bizarre behaviour [LSD]
Compulsive behaviour [amphetamine]
Constipation [heroin]
Crawling sensations [cocaine]
Dreamy, self-absorbed, head-nodding [heroin]
Dreamy, spaced out, giggly, distorted perception of all senses especially time, hungry for sweet things, slow thinking [marijuana]
Depression [amphetamine, LSD]
Dilated pupils (sometimes) [amphetamine, cocaine, LSD]
Dry mouth, great thirst [amphetamine, cannabis]
Flushed (sometimes) [amphetamine, heroin]
Increased appetite [cannabis]
Insomnia [amphetamine]
Loss of bodily co-ordination [solvents, LSD, cannabis]
Loss of appetite [amphetamine]
Nausea [cannabis]
Pin-prick pupils [heroin]
Paranoia [amphetamine, cannabis, cocaine]
Restless and or very talkative [amphetamine]
Rapid, repetitive speech [amphetamine]
Running nose [heroin]
Skin very pale [solvents, cannabis]
Sweating a lot [heroin, amphetamine]
Shaking a lot [heroin, cocaine, LSD]
Urinating frequently [amphetamine]

Drug use and abuse
Untangling the 'how' and 'why' of a person's drug use is rarely an easy task, but most people use a drug because they enjoy the effects. This may seem like a simplistic statement, but it's a fact that's easily forgotten by a person's family and friends who are very concerned and try to understand why someone close to them is using drugs.

Psychological addiction
Giving up drugs as it is presented in movies or the press usually focuses on the immediate effects of withdrawing from a drug like heroin. It's important to remember that there's often more to an addiction than the physical withdrawal symptoms.

The term 'craving' is often used when talking about addiction. Often a person using a drug knows that by using the drug all manner of problems seem to go away, it's not surprising that they develop an overwhelming desire to use and that this can dominate their thoughts.

Physical addiction
The physical effects of withdrawal from strong drugs have been portrayed in several films. It is rightly shown as an unpleasant and difficult experience - and a good reason not to experiment in the first place.

It is possibly ironic that alcohol, barely perceived as a drug at all, has much worse and more dangerous withdrawal effects. Getting off drugs often requires considerable support. It's possible, but very rare, for someone experiencing heroin withdrawal to need to be admitted to hospital. Someone who is physically addicted to alcohol (not normally younger people) should not attempt to stop using it without consulting a doctor.

The length and severity of withdrawal differs from person to person according to the drug, how much has been taken and for how long. For most addicts, their problem is a mixture of both physical and psychological aspects and in some cases it's hard to distinguish between the two. The stimulants cocaine and amphetamine are classic examples of this - people coming down after using these drugs feel very low and lack energy. When a person takes cocaine, they feel very high and use up lots of energy; their feelings afterwards could be partly because of feeling tired and adjusting to a normal mood again, but there are other theories that suggest these feelings are because the body is re-establishing its normal chemical balance.

The long term effects of drug use can be extreme.

What can I do to help myself?
Admitting you have a problem is half of solving the problem. The next step is to get support.

If you're physically addicted, it may be dangerous just to stop - especially if you're using alcohol or tranquillisers. Even if it isn't dangerous to stop abruptly, a doctor may be able to prescribe medication to help you through the first phase of withdrawal.

Sources of support

The National Drugs Helpline
Free help and advice 24 hours a day, seven days a week.
Tel: 0800 776600
Website: http://www.talktofrank.com

Narcotics Anonymous
A self-help group run by recovering addicts with a network of meetings across the country
Helpline: 0845 373 3366
Website: http://www.ukna.org

Families Anonymous
Support for the relatives and friends of people with drug problems.
Helpline: 0845 120 0660
Website: http://www.famanon.org.uk

Other helpful advice and addresses can be found in the BBC's online Addictions guide.