Every drug has the potential to do harm as well as good. When doctors consider prescribing a drug, they must weigh the possible risks against the expected benefits. Use of a drug is not justified unless the expected benefits outweigh the possible risks. Doctors must also consider the likely outcome of withholding the drug. Potential benefits and risks can never be determined with mathematical precision.

When assessing the benefits and risks of prescribing a drug, doctors consider the severity of the disorder being treated and the effect it is having on the person's quality of life. For example, for relatively minor disorders—such as coughs and colds, muscle strains, or infrequent headaches—only a very low risk of adverse drug reactions is acceptable. For such symptoms, over-the-counter drugs are usually effective and well tolerated. When used according to directions, over-the-counter drugs for treating minor disorders have a wide safety margin (the difference between the usual effective dose and the dose that produces severe adverse drug reactions). In contrast, for serious or life-threatening disorders (such as a heart attack, stroke, cancer, or organ transplant rejection), a higher risk of a severe adverse drug reaction is usually acceptable.

Last full review/revision October 2012 by Joan B. Tarloff, PhD