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 a drug would be aimed precisely at a disease site and would not harm healthy tissues. Although many new medications are aimed more accurately than their predecessors, none of them, as of yet, hit the target exclusively.
Most medications produce several effects, but usually only one effect—the therapeutic effect—is wanted for the treatment of a disorder. The other effects may be regarded as unwanted, whether they are intrinsically harmful or not. For example, certain antihistamines cause drowsiness as well as control the symptoms of allergies. When an over-the-counter sleep aid containing an antihistamine is taken, drowsiness is considered a therapeutic effect. But when an antihistamine is taken to control allergy symptoms during the daytime, drowsiness is considered an annoying, unwanted effect.
Most people, including health care practitioners, refer to unwanted effects as side effects; another term used is adverse drug effect. However, the term adverse drug reaction is technically more appropriate for drug effects that are unwanted, unpleasant, noxious, or potentially harmful.
Prevalence of adverse drug reactions
Not surprisingly, adverse drug reactions are common. Most adverse drug reactions are relatively mild, and many disappear when the medication is stopped or the dose is changed. Some gradually subside as the body adjusts to the medication. Other adverse drug reactions are more serious and last longer. According to the National Electronic Injury Surveillance System–Cooperative Adverse Drug Event Surveillance Project (NEISS–CADES), there were an estimated 6 emergency department (ED) visits for medication harms per 1000 persons per year in the period from 2017 to 2019. About 39% of these visits resulted in hospitalization. In previous estimates in the United States, 3 to 7% of all hospital admissions were for treatment of adverse drug reactions. Adverse drug reactions occur during 10 to 20% of hospital admissions, and about 10 to 20% of these reactions are severe. These statistics do not include the number of adverse drug reactions that occur in people who live in nursing homes and other care facilities.
Although the exact number of adverse drug reactions is not certain, they clearly represent a significant public health problem that is often preventable.
According to the World Health Organization, fatal adverse drug reactions occur mainly in people older than 75 years of age. Prescription errors and inability or failure to take correctly prescribed medications as indicated both contribute to the incidence of ADRs.
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Common adverse drug reactions
Digestive disturbances—loss of appetite, nausea, a bloating sensation, constipation, and diarrhea—are particularly common adverse drug reactions, because most drugs and medications are taken by mouth and pass through the digestive tract. However, almost any organ system can be affected. In older people (see Aging and Drugs), the brain is commonly affected, often resulting in drowsiness and confusion.
Identification and reporting of adverse drug reactions
Many adverse drug reactions are identified when a drug is being tested before it is submitted to the Food and Drug Administration (FDA) for approval. Other adverse drug reactions, typically those that are uncommon, are not detected until the medication has been on the market long enough to be used by a large number of people. Thus, health care providers are required to report suspected adverse drug reactions to the FDA.
Some Serious Adverse Drug Reactions
Adverse Drug Reaction | Types of Drugs | Examples |
|---|---|---|
Anemia (resulting from decreased production or increased destruction of red blood cells) | Certain antibiotics | Chloramphenicol |
Medications used to treat malaria or tuberculosis in people with G6PD enzyme deficiency | ||
Angioedema (swelling of the lips, tongue, and throat causing difficulty breathing) | ACE inhibitors | |
Proton pump inhibitors | ||
Birth control medications (all forms including patches and pills) | ||
Confusion and drowsiness | Sedatives, including many antihistamines | |
Antidepressants (especially in older people) | ||
Decreased production of white blood cells, with increased risk of infection | Certain antipsychotic drugs | |
Chemotherapy drugs | ||
Some medications used to treat thyroid disorders | ||
NSAIDs (repeated use of excessive doses) | ||
Aminoglycoside antibiotics | ||
Some chemotherapy drugs | ||
Antifungals | ||
Some other antibiotics | ||
Some analgesics | ||
Some medications used to treat tuberculosis | ||
Iron supplements (in excessive amounts) | Ferrous sulfate, ferrous fumarate | |
Antidepressants | ||
Antibiotics | ||
Muscle tissue destruction (rhabdomyolysis) | Statins | |
Stomach or intestinal ulcers (with or without bleeding) | NSAIDs | |
Anticoagulants | ||
Bisphosphonates | ||
Some antibiotics | Penicillins Quinolones Sulfonamides | |
Anticonvulsants | ||
Antiarrhythmics | ||
Antipsychotics | ||
ACE = angiotensin-converting enzyme; G6PD = glucose-6-phosphate dehydrogenase; NSAIDs = nonsteroidal anti-inflammatory drugs. | ||
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
American Association of Poison Control Centers: Access to information on a variety of poisons, an emergency helpline (1-800-222-1222), and tips on prevention.
FDA Adverse Event Reporting System (FAERS): Access to Questions and Answers on FDA's Adverse Event Reporting System (FAERS).
