In general, medicines work by:

• Replacing substances that are deficient or missing in the body,
• Altering the activity of cells, or
• Destroying infectious micro-organisms or abnormal cells

Replacing substances that are deficient or missing in the body
The body needs certain levels of proteins (or amino acids), vitamins and minerals in order to work normally. If these important substances are insufficient or lacking, this can lead to medical disorders. These are called ‘deficiency disorders’. Examples include: iron deficiency (anaemia), and vitamin C deficiency (scurvy).

Deficiency disorders can also occur as a result of a lack of hormones in the body (hormone deficiencies). Common examples include: diabetes (insulin deficiency) and hypothyroidism (thyroid hormone deficiency).

Deficiency disorders can be treated with medicines or hormones that replace or restore the levels of the missing substances, for example insulin injections for diabetics.

Altering the activity of cells
Cells are the basic ‘building blocks’ of the body. All human tissue is made up of groups of cells.

Many medicines work by altering the activity of cells. For example, anti-inflammatory medicines such as ibuprofen and diclofenac block the action or stop the production of chemical substances (mediators) which are released by cells in response to tissue damage and which cause inflammation and pain.

Medicines which interfere with the way cells work are used to treat a variety of conditions, such as blood clotting disorders (eg. anti-coagulants ), heart (eg. calcium channel blockers ) and kidney diseases.

Some medicines work by attaching themselves (binding) to sites found on the surface of cells (receptors) and either increase or decrease the activity of the cell (eg. medicines used in the treatment of epilepsy and Parkinson’s disease).

Destroying infectious microorganisms or abnormal cells
Infectious diseases occur when viruses, bacteria, protozoa or fungi invade the body.  Antibiotics e.g. penicillin can destroy bacteria by killing them directly or by preventing them multiplying. Anti-fungals commonly used for infections of the skin and mouth (eg. clotrimazole and miconazole) work by disrupting infected cells. Other medicines work by killing abnormal cells, for example some anti-cancer drugs directly target and kill harmful cancer cells.