In medicine, an adverse effect is a harmful and undesired effect that results from a therapy like medication, chemotherapy, surgery or other intervention. An adverse effect may be called a "side-effect" (when it is less important than the therapeutic effect).

It may result from an unsuitable or incorrect dosage or procedure (which could be caused by medical error). Some adverse effects happen only at the beginning or a change of a treatment.

Reporting systems
In many countries, adverse effects have to be reported and researched in clinical trials and included into the patient information accompanying medical devices and drugs for sale to the public.

Examples of adverse effects associated with specific medications

 Abortion, miscarriage or uterine hemorrhage associated with misoprostol (Cytotec®), a labor-inducing drug (this is a case where the adverse effect has been used legally and illegally for performing abortions)
 Addiction to many sedatives and analgesics such as diazepam, morphine, etc.
 Birth defects associated with Thalidomide and Accutane.
 Bleeding of the intestine associated with aspirin therapy
 Cardiovascular disease associated with COX-2 inhibitors (i.e. Vioxx)
 Deafness and kidney failure associated with gentamicin (an antibiotic)
 Death, following sedation in children using propofol (Diprivan®)
 Dementia associated with heart bypass surgery
 Depression or hepatic injury caused by interferon
 Diabetes caused by atypical antipsychotic medications (neuroleptic psychiatric drugs)
 Diarrhea caused by the use of orlistat (Xenical®)
 Erectile dysfunction associated with many drugs, such as antidepressants
 Fever associated with vaccination (in the past, imperfectly manufactured vaccines, such as BCG and poliomyelitis, have caused the very disease they intended to fight).
 Glaucoma associated with corticosteroid-based eye drops
 Hair loss and anemia may be caused by chemotherapy against cancer, leukemia, etc.
 Headache following spinal anesthesia
 Hypertension in ephedrine users, which prompted FDA to remove the status of dietary supplement of ephedra extracts
 Insomnia caused by stimulants, Ritalin®, Adderall®, etc.
 Lactic acidosis associated with the use of stavudine (Zerit®, for anti-HIV therapy) or metformin (for diabetes)
 Liver damage from paracetamol
 Melasma and thrombosis associated with use of estrogen-containing hormonal contraception such as the combined oral contraceptive pill
 Rhabdomyolysis associated with statins (anti-cholesterol drugs)
 Seizures caused by withdrawal from benzodiazepine
 Drowsiness or increase in appetite due to antihistamine use.  Some antihistamines are used in sleep aids explicitly because they cause drowsiness.
 Stroke or heart attack associated with sildenafil (Viagra®) when used with nitroglycerine
 Suicide, increased tendency associated to the use of fluoxetine and other SSRI antidepressants
 Tardive dyskinesia associated with long-term use of metoclopramide and many antipsychotic medications

Related pages

 Toxicology

Other websites
 Patient Safety Network. An extremely useful site, with a glossary and articles on all kinds of threats to patient safety, including adverse effects, drug reactions, medical error, iatrogenesis, etc.
 Australian Adverse Drug Reactions Bulletin  - published bimonthly by ADRAC
 Drugs of Concern  DrugIntel.com site for tort lawyers with up-to-date information on drugs that cause severe adverse effects)
 Medication Errors a FDA site.
 Medical Product Safety Information. MedWatch, a useful page from Food and Drug Administration, listing safety alerts for drugs, biologics, devices and dietary supplements, recalls, market withdrawals, public health advisories, links to the VAERS and MAUDE databases, etc.)
 Medical Devices Safety National Library of Medicine (Medline Plus, useful lists of conventional drug and medical device articles and websites)
 When Medicine Hurts Instead of Helps  - A special report by the Alliance for Aging Research on ADRs.

Medicine