Find information on medical topics, symptoms, drugs, procedures, news and more, written in everyday language.

* This is the Consumer Version. *

Overview of Adverse Drug Reactions

by Joan B. Tarloff, PhD

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 drugs are aimed more accurately than their predecessors, none of them, as of yet, hit the target exclusively.

Most drugs 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 event. However, the term adverse drug reaction is technically more appropriate for drug effects that are unwanted, unpleasant, noxious, or potentially harmful.

Not surprisingly, adverse drug reactions are common. Most adverse drug reactions are relatively mild, and many disappear when the drug is stopped or the dose is changed. Some gradually subside as the body adjusts to the drug. Other adverse drug reactions are more serious and last longer. About 3 to 7% of all hospital admissions in the United States are 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.

Digestive disturbances—loss of appetite, nausea, a bloating sensation, constipation, and diarrhea—are particularly common adverse drug reactions, because most drugs 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.

Some 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 drug has been on the market long enough to be used by a large number of people. Thus, doctors 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

Drugs used to treat malaria or tuberculosis in people with G6PD enzyme deficiency

Chloroquine

Isoniazid

Primaquine

Angioedema (swelling of the lips, tongue, and throat causing difficulty breathing)

ACE inhibitors

Captopril

Enalapril

Lisinopril

Bone fractures

Proton pump inhibitors

Esomeprazole

Lansoprazole

Omeprazole

Blood clots

Birth control drugs (all forms including patches and pills)

Drospirenone/ethinyl estradiol

Norelgestromin/ethinyl estradiol

Confusion and drowsiness

Sedatives, including many antihistamines

Diphenhydramine

Antidepressants (especially in older people)

Amitriptyline

Imipramine

Decreased production of white blood cells, with increased risk of infection

Certain antipsychotic drugs

Clozapine

Chemotherapy drugs

Cyclophosphamide

Mercaptopurine

Methotrexate

Vinblastine

Some drugs used to treat thyroid disorders

Propylthiouracil

Kidney damage

NSAIDs (repeated use of excessive doses)

Ibuprofen

Ketoprofen

Naproxen

Aminoglycoside antibiotics

Gentamicin

Kanamycin

Some chemotherapy drugs

Cisplatin

Methotrexate

Antifungals

Amphotericin B

Some antibiotics

Gentamicin

Tetracycline (outdated)

Liver damage

Some analgesics

Acetaminophen (use of excessive doses)

Some drugs used to treat tuberculosis

Isoniazid

Iron supplements (in excessive amounts)

Antidepressants

Duloxetine

Antibiotics

Tetracycline

Muscle tissue destruction (rhabdomyolysis)

Statins

Atorvastatin

Simvastatin

Stomach or intestinal ulcers (with or without bleeding)

NSAIDs

Aspirin

Ibuprofen

Ketoprofen

Naproxen

Anticoagulants

Heparin

Warfarin

Bisphosphonates

Alendronate

Etidronate

Risedronate

Some antibiotics

Penicillins

Quinolones

Anticonvulsants

Phenytoin

Valproic acid

Ventricular tachycardia (see Ventricular Tachycardia)

Antiarrhythmics

Amiodorone

Procainamide

Sotalol

Antipsychotics

Chlorpromazine

Haloperidol

Lithium

ACE = angiotensin-converting enzyme; G6PD = glucose-6-phosphate dehydrogenase; NSAIDs = nonsteroidal anti-inflammatory drugs.

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • ACHROMYCIN V
  • No US brand name
  • ARALEN
  • BETAPACE
  • PREVACID
  • ADVIL, MOTRIN IB
  • ZOCOR
  • CYTOXAN (LYOPHILIZED)
  • PRINIVIL, ZESTRIL
  • FOSAMAX
  • PANHEPRIN
  • PLATINOL
  • DIDRONEL
  • ALEVE, NAPROSYN
  • LANIAZID
  • NEXIUM
  • PRILOSEC
  • OTREXUP
  • GENOPTIC
  • HALDOL
  • TYLENOL
  • PURINETHOL
  • ACTONEL
  • ESTRADERM, ESTROGEL, VIVELLE
  • CLOZARIL
  • CYMBALTA
  • NEXCEDE
  • COUMADIN
  • DILANTIN
  • CAPOTEN
  • VASOTEC
  • LITHOBID
  • TOFRANIL
  • LIPITOR