Drugs Change Your Body Chemistry
Drugs alter what goes on in your body. You body's essentially a seething mass of chemical reactions - drugs can interfere with these reactions, sometimes fatally. Many drugs are derived from natural substances found in plants, and have been known and used for centuries e.g. heroin is derived from a chemical found in a species of poppy. Some of the chemical changes caused by drugs can lead to the body becoming addicted to the drug. If the drug isn't taken, an addict can suffer physical withdrawal symptoms - and these are sometimes very unpleasant. Heroin and cocaine are very addictive, so are nicotine and caffeine.
Testng Medical Drugs
Computer models are often used in the early stages - these stimulate a human's response to a drug. This can identify promising drugs to be tested in the next stage (but sometimes it's not as accurate as actually seeing the effect on a live organism). Drugs are then developed further by testing on human tissues in the lab. However, you can't use human tissue to test drugs that affect whole or multiple body systems, e.g. testing a drug for blood pressure must be done on a whole animal because it has an intact circulatory system.The next step is to develop and test the drug using live animals. The law in Britain states it must be tested on two different live mammals. Some people think it's cruel to test on animals, but others believe this is the safest way to make sure a drug isn't dangerous before it's given to humans. It is then tested on human volunteers in a clinical trial - this should determine whether there are any side effects.