Types of drug

A drug is a substance taken into the body that modifies or affects chemical reactions in the body. Some drugs are beneficial, while others are harmful.

Type of drugEffect on bodyExample Depressant Slows down nerve and brain activity Alcohol, solvents, temazepam Hallucinogen Alters what we see and hear LSD Painkiller Blocks nerve impulses Aspirin, paracetamol Performance enhancer Improves muscle development Anabolic steroids Stimulant Increases nerve and brain activity Nicotine, caffeine, ecstasy

Stimulants and depressants affect the synapses between neurones in the nervous system:

• stimulants cause more neurotransmitter molecules to diffuse across the synapse
• depressants stop the next neurone sending nerve impulses. They bind to the receptor molecules the next neurone that needs to respond to the neurotransmitter molecules.

Classification of drugs

Some drugs are illegal, or must only be prescribed by a doctor. Some prescription drugs are misused and taken for recreational use, rather than for medical reasons. They become illegal under these circumstances.

Illegal drugs are classified from Class A to Class C. Class A drugs are the most dangerous, with the most serious penalties for possession or dealing. Class C are the least dangerous, with the lightest penalties, but this does not mean they are safe to use.

Drug testing

Certain drugs can be extracted from natural sources, and have been known about for a long time. For example, willow bark was used by the ancient Greeks to help cure fevers and pains. It was later discovered that the active ingredient was salicylic acid. This was modified by chemists into the substance we call aspirin, which is less irritating to the stomach than salicylic acid.

Molecular structure of salicylic acid and aspirin

New medical drugs have to be tested to ensure that they work, and are safe, before they can be prescribed.

Three stages of testing drugs

There are three main stages of testing:

1. The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work.
2. Drugs that pass the first stage are tested on animals. In the UK, new medicines have to undergo these tests. But it is illegal to test…