Drug

A chemical substance that alters the function of one or more body organs or the process of a disease. Drugs include prescribed medicines, over-thecounter remedies, and substances (such as alcohol, tobacco, and drugs of abuse) that are used for nonmedical purposes. Drugs normally have a chemical name, an officially approved generic name (see generic drug), and often a brand name. Drugs for medical use are either licensed for prescription by a doctor only or can be bought over the counter at a chemist’s or supermarket. Most drugs are artificially produced to ensure a pure preparation with a predictable potency (strength). Some drugs are genetically engineered. A drug is classified according to its chemical make-up or the disorder it treats or, according to its specific effect on the body. All new drugs are tested for their efficiency and safety. In the UK, drugs are licensed by the Medicines Control Agency (MCA). A licence may be withdrawn if toxic effects are reported or if the drugs causes serious illness. Drugs can be used to relieve physical or mental symptoms, to replace a deficient natural substance, or to stop the excessive production of a hormone or other body chemical. Some drugs are given to destroy foreign organisms, such as bacteria. Others, known as vaccines, are given to stimulate the body’s immune system to form antibodies. Drugs are given by mouth, by injection, or applied directly to the affected site via transdermal, nasal, and other direct routes (for example, to the lungs through an inhaler). Injected drugs have a more rapid effect than drugs taken by mouth because they enter the bloodstream without passing first through the digestive system. Unabsorbed drugs taken by mouth are excreted in the faeces. Drugs that have entered the bloodstream are eliminated in urine. Some drugs interact with food or alcohol or other drugs. Most drugs can produce adverse effects. These effects may wear off as the body adapts to the drug. Adverse effects are more likely if there is a change in the absorption, breakdown, or elimination of a drug (caused, for example, by liver disease). Unexpected reactions sometimes occur due to a genetic disorder, an allergic reaction, or the formation of antibodies that damage tissue. Many drugs cross the placenta; some affect growth and development of the fetus. Most drugs pass into the breast milk of a nursing mother, and some will have adverse effects on the baby.