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A medicine is commonly defined as a substance or preparation that can treat or prevent disease. Historically, most medicines were made from natural products. Advances in the last two centuries have led to the introduction of man-made chemical medicines, biologics and gene therapies. In addition, new technologies, such as tissue engineering , which uses living cells to repair tissues or organs, and nanomedicine , which uses tiny ‘nano’ particles in a variety of healthcare settings, have increased the options available.

These training materials provide short descriptions of the different types of medicine, how they work and how they are developed.

Synthetic Chemical Medicines

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Chemical medicines comprise man-made molecules created in the laboratory by combining small atoms in a specific sequence and structure. Commonly used atoms include carbon, oxygen, hydrogen and nitrogen, and are usually obtained from petrochemicals derived from crude oil and natural gas liquids. In contrast to some other medicines, chemical medicines are not produced by living cells such as bacteria. In fact, chemical medicines are usually quite simple in design and are produced using chemical processes in large quantities in specialist manufacturing facilities (Figure 1). Many have been used by patients for many decades.


Figure 1.
 a) Simple structure of the chemical molecule paracetamol and b) the more complex structure of the biologic medicine insulin.

Semi-synthetic Chemical Medicines

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As discussed in the introduction, natural substances, which may be extracted from plants, bacteria or animal cells, can have medicinal properties, but may not make ideal medicines. Semi-synthetic medicines are produced by the chemical modification of naturally occurring substances to overcome some of their limitations. This method of production distinguishes semi-synthetic medicines from fully or totally synthetic medicines (man-made chemical medicines created entirely in the laboratory, see the section on chemical medicines) and fully natural compounds, such as the herbal remedy St John’s wort (Hypericum perforatum) (used without any additional chemical modification). Semi-synthetic medicines may therefore be regarded as intermediates between natural and synthetic substances.


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A biologic medicine is defined by European legislation as ‘a medicine that contains one or more active substances made by or derived from a biological source’. Biological, or natural, sources include microorganisms, animal cells or human cells. Some biologic medicines mimic proteins made naturally in the human body. Examples include insulin, growth hormone and growth factors that control blood cell production. Other biologic medicines are not copies of proteins occurring naturally in the human body, but are enhanced in the laboratory to improve bioavailability, specificity, and effectiveness. The best-known examples of these are antibodies, which bind to the surface of cells in the body and are used extensively in the treatment of cancer.

Biologic medicines in the broadest sense include any substance made in the laboratory from a living organism. This broad definition includes vaccines, immunotherapies, biosimilars, gene therapy and stem cell or tissue therapy. In this section, however, biologic medicines will refer to protein-based medicines, such as insulin, while the other substances covered in the broad definition will be described separately in different sections.

Generics and Biosimilars

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A vaccine is a biological preparation, usually given by injection, which improves or conveys immunity to a particular disease. Most vaccines are made from dead or weakened viruses or bacteria, from fragments of these microorganisms or from the toxins they produce. Vaccines are quite different from chemical medicines; they usually have much more complex molecular structures than chemical medicines because they are produced through natural processes. In contrast to most chemical medicines, they are frequently given to healthy individuals and normally aim to prevent rather than cure disease. Therefore, it is important to ensure that any risks of side effects are minimal.


The potential for vaccines to save lives was first discovered in the late 18th century, when Edward Jenner noticed that milkmaids who had previously contracted the cowpox virus seemed to be resistant to the similar, but more deadly, smallpox virus. To test his theory, he infected 8-year-old James Phipps with cowpox and then later attempted to infect him with smallpox. As expected, Phipps did not develop the smallpox virus, proving Jenner’s hypothesis to be correct. A global vaccination plan was implemented in the 20th century, which eradicated smallpox.1 Vaccines are now available for preventing many previously devastating diseases, such as polio, typhoid, measles and tuberculosis, and have saved millions of lives worldwide. Indeed, today, vaccines are being used not only to prevent diseases, but also to treat diseases as well, such as cancer.

Medical Devices and Medicine-Device Combinations

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The spectrum of medical devices ranges from a simple pair of spectacles to improve eyesight, to the technologically complex magnetic resonance imaging (MRI ) machine used to examine organs inside the body. The World Health Organization and European Union definitions of medical devices can be condensed to:

An article, instrument, apparatus or machine that is used in the prevention, diagnosis or treatment of illness or disease, or for detecting, measuring, restoring, correcting or modifying the structure or function of the body for some health purpose.

medical device

Figure 1.

Typically, medical devices are used when medicines alone cannot achieve the desired effect. However, medicine/medical-device combinations (often referred to as medicine–device) exist, such as the salbutamol–inhaler combination used by patients with asthma , and the adrenaline–injector combination for the treatment of anaphylaxis (a severe allergic reaction).


Medical devices have been in existence for thousands of years. Records show the ancient Egyptians used scalpels, slings, splints and crutches as far back as 7000 BC. Some of the significant milestones in the development of medical devices are shown in Figure 2.

medical device development

Figure 2. Timeline of medical device development.

Gene Therapy

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Gene therapy is a way of restoring function in cells where genes are missing or not working properly. Genes contain all of the information for building and maintaining cells and are encoded by deoxyribonucleic acid (DNA ). The nucleus of every cell contains twenty-three pairs of chromosomes, in which thousands of genes are located. Certain diseases are caused by small changes in the DNA of our genes, known as genetic mutations. Mutations occur when information encoded by our genes gets copied incorrectly and this can lead to the production of faulty proteins which cause disease. Gene therapy is used to solve the problem at the source. This means that diseased tissues and organs can then work properly.


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