In medicine, an indication is a valid reason to use a certain test, medication, procedure, or surgery. The opposite of an indication is a contraindication, a reason to withhold a certain medical treatment because it could harm a patient.
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Drugs
Most countries and jurisdictions have a licensing body whose duty is to determine whether to approve a drug for a specific indication, based on the relative safety of the drug and its efficacy for the particular use. In the United States, indications for medications are regulated by the Food and Drug Administration (FDA), and are included in the package insert under the phrase "Indications and Usage". The European Medicines Agency (EMA) holds this responsibility for centrally authorized drugs in the European Union.
There are different classes of indication of drugs depending on validity of the benefit gained by the use of specific drug. If a drug's use is officially indicated it is "FDA approved" (also called 'labeled') and if prescribed for other conditions the term "non-approved" (or 'off-label') is used. As the evidence and consensus to use the drug increases, its class of indication is improved. Preferred drugs (and other treatments) are also referred to a "first line" or "primary" while others are called "second line", "third line" etc. A drug may be indicated as an "adjunct" or "adjuvant", added to a first line drug.
Medical tests
Each test has its own indications and contraindications, but in a simplified fashion, how much a test is indicated for an individual depends largely on its net benefit for that individual, which largely depends on the absolute difference between pre- and post-test probability of conditions (such as diseases) that the test is expected to achieve. Additional factors that influence a decision whether a medical test should be performed or not include: cost of the test, time taken for the test or other practical or administrative aspects. The possible benefits of a diagnostic test may also be weighed against the costs of unnecessary tests and resulting unnecessary follow-up and possibly even unnecessary treatment of incidental findings. Also, even if not beneficial for the individual being tested, the results may be useful for the establishment of statistics in order to improve health care for other individuals.