Merck Manual

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Benefits Versus Risks of Drugs


Daphne E. Smith Marsh

, PharmD, BC-ADM, CDCES, University of Illinois at Chicago College of Pharmacy

Reviewed/Revised Mar 2023

Every medication has the potential to do harm (an adverse drug reaction Overview of Adverse Drug Reactions Adverse drug reactions (adverse effects) are any unwanted effects of a drug or medication. In the early 1900s, German scientist Paul Ehrlich described an ideal drug as a "magic bullet." Such... read more ) as well as good. When doctors consider prescribing a medication, they must weigh the possible harms against the expected benefits. Use of a medication is not justified unless the expected benefits outweigh the possible harms. Doctors must also consider the likely outcome of withholding the medication. Potential benefits and harms can never be determined with mathematical precision.

When assessing the benefits and risks of prescribing a medication, 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 medications are usually effective and well tolerated. When used according to directions, over-the-counter medications 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 Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) , stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more , cancer Overview of Cancer A cancer is an abnormal growth of cells (usually derived from a single abnormal cell). The cells have lost normal control mechanisms and thus are able to multiply continuously, invade nearby... read more , or organ transplant rejection Rejection Transplantation is the removal of living, functioning cells, tissues, or organs from the body and then their transfer back into the same body or into a different body. The most common type of... read more ), a higher risk of a severe adverse drug reaction is usually more acceptable.

Individuals may have different perspectives on quality of life and the risks they are willing to assume. For example, some people are more willing than others to accept the adverse effects of certain cancer chemotherapy in return for a slight chance of prolonging life. People also differ on how great a possibility of risk they are willing to accept. For example, a 1 in 50 chance of having serious bleeding from a medication may be unacceptable to some people but seem reasonable to others.

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