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A drug is a chemical that has an effect on the body.

Everybody thinks that drugs are just the illegal sort. But they also include useful medicines and also legal drugs.

Legal drugs

The drugs that society decides are dangerous or addictive are made illegal. Using these drugs is a crime.

These are the 'street' drugs (cannabis, cocaine and heroin for example).

Different societies at various times have different views on which drugs should be illegal.

The most obvious are the medicinal drugs, such as Penicillin, that are designed to deal with medical conditions. These are always rigorously tested, checked and their use reviewed.

However other substances in common usage are drugs too:

Caffeine is a widely used drug, but its overuse can cause tissue damage.

Likewise tobacco and alcohol are legal drugs in most countries. Yet they too can have serious health effects.

Drugs that affect our nervous systems and our mood can become addictive or habit-forming.

However the word 'addictive' is often seen as just relating to illegal drugs. Therefore the word dependence is seen as a better alternative.

Drug dependence has two features:

  1. Chemical dependence
  2. Psychological dependence

This is where the body itself adapts to the presence of the drug. When the chemical is removed the body is no longer able to function normally.

The body then goes into withdrawal symptoms such as hallucinations, fevers, nausea (feeling sick) and shakes. These are real, physical signs.

Chemical dependence

Another term for chemical dependence is physiological dependence. Physiology is how the body functions normally.

This form of dependence is where the person feels a need for the drug. They may also feel unable to cope without the drug.

For example: some smokers need to chew sweets after they give up because they miss having a cigarette in their mouths.

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