In medicine, a contraindication is a condition or factor that serves as a reason to withhold a certain medical treatment due to the harm that it would cause the patient. Contraindication is the opposite of indication, which is a reason to use a certain treatment.
Absolute contraindications are contraindications for which there are no reasonable circumstances for undertaking a course of action. For example, children and teenagers with viral infections should not be given aspirin because of the risk of Reye's syndrome, and a person with an anaphylactic food allergy should never eat the food to which they are allergic. Similarly, a person with hemochromatosis should not be administered iron preparations.
Relative contraindications are contraindications for circumstances in which the patient is at higher risk of complications from treatment, but these risks may be outweighed by other considerations or mitigated by other measures. For example, a pregnant woman should normally avoid getting X-rays, but the risk may be outweighed by the benefit of diagnosing (and then treating) a serious condition such as tuberculosis. Relative contraindications may also be referred to as cautions, such as in the British National Formulary.
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