Medicinal drugs are substances that can cure, arrest, or prevent disease, relieve symptoms, or help in the diagnosis of disorders. There are a huge number of drugs available, and new drugs are continually being developed that are more effective at restoring health and saving lives than ever before.
In this section
Modern drug therapy began when scientists discovered how to isolate the active ingredients in plant sources and how to create synthetic versions of those substances. This new technology, together with a better understanding of how the body functions both in health and in disease, has enabled the development of drugs that can target specific processes in the body.
Before any new drug is marketed, it is thoroughly tested. The effects that the drug has on people are measured either against the existing standard treatment or against a placebo (an inactive substance that looks and tastes exactly like the drug).
In the UK, drugs are approved and licensed by the Committee on Safety of Medicines (CSM). A new drug is approved only if it is shown to be safe and effective. The CSM can withdraw a drug from the market if it later proves to cause unacceptable side effects.
How drugs work
Drugs act in a variety of ways. Some kill or halt the spread of invading organisms, such as bacteria, fungi, and viruses. These drugs include antivirals, antifungals, and antibiotics. Other drugs, known as cytotoxic drugs, kill cells as they divide or prevent their replication. Cytotoxic drugs are mainly used in the treatment of cancer.
Some drugs simply supplement missing or low levels of natural body chemicals such as certain hormones or vitamins. Another group of drugs alters the effectiveness of certain body chemicals. These drugs work either by mimicking the action of natural chemicals to increase their effect or by blocking their action to decrease their effect (see How drugs act on receptors). Drugs may also affect the part of the nervous system that controls a particular process, such as the brain’s vomiting centre to relieve vomiting.
How drugs are used
There are various different ways in which drugs may be delivered to their intended site of action. Some, such as eyedrops or topical skin preparations, can be applied directly to the target area. These preparations tend to have a very localized effect and do not usually enter the bloodstream in significant quantities. Other preparations are introduced into the bloodstream, which circulates them to their target area in the body. These drugs may be delivered by different routes, depending on which is the most effective way to reach the target area and on how the drugs are metabolized (see Drug metabolism).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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