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In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequences of the use of a drug.
Occasionally, drugs are prescribed or procedures performed specifically for their side effects; in that case, said side effect ceases to be a side effect, and is now an intended effect. For instance, X-rays were historically (and are currently) used as an imaging technique; the discovery of their oncolytic capability led to their employ in radiotherapy (ablation of malignant tumours).
Frequency of side effects
- Very common >=1/10
- Common (frequent) >=1/100 and <1/10
- Uncommon (infrequent) >=1/1000 and <1/100
- Rare >=1/10000 and <1/1000
- Very rare <1/10000
Examples of therapeutic side effects
- Bevacizumab (Avastin), used to slow the growth of blood vessels, has been used against dry age-related macular degeneration, as well as macular edema from diseases such as diabetic retinopathy and central retinal vein occlusion.
- Buprenorphine has been shown experimentally (1982–1995) to be effective against severe, refractory depression.
- Bupropion (Wellbutrin), an anti-depressant, is also used as a smoking cessation aid; this indication was later approved, and the name of the smoking cessation product is Zyban. In Ontario, Canada, smoking cessation drugs are not covered by provincial drug plans; elsewhere, Zyban is priced higher than Wellbutrin, despite being the same drug. Therefore, some physicians prescribe Wellbutrin for both indications.
- Carbamazepine is an approved treatment for bipolar disorder and epileptic seizures, but it has side effects useful in treating attention-deficit hyperactivity disorder (ADHD), schizophrenia, phantom limb syndrome, paroxysmal extreme pain disorder, neuromyotonia, and post-traumatic stress disorder.
- Dexamethasone and Betamethasone in premature labor, to enhance pulmonary maturation of the fetus.
- Doxepin has been used to treat angiodema and severe allergic reactions due to its strong antihistamine properties.
- Gabapentin, approved for treatment of seizures and postherpetic neuralgia in adults, has side-effects which are useful in treating bipolar disorder1, essential tremor, hot flashes, migraine prophylaxis, neuropathic pain syndromes, phantom limb syndrome, and restless leg syndrome.
- Hydroxyzine, an antihistamine, is also used as an anxiolytic.
- Magnesium sulfate in obstetrics for premature labor and preeclampsia.
- Methotrexate (MTX), approved for the treatment of choriocarcinoma, is frequently used for the medical treatment of an unruptured ectopic pregnancy.
- The SSRI medication sertraline is approved as an antidepressant but delays conjugal climax in men, and thus may be supplied to those in which climax is premature.
- Sildenafil was originally intended for pulmonary hypertension; subsequently, it was discovered that it also produces erections, for which it was later marketed.
- Terazosin, an α1-adrenergic antagonist approved to treat benign prostatic hyperplasia (enlarged prostate) and hypertension, is (one of several drugs) used off-label to treat drug induced diaphoresis and hyperhidrosis (excessive sweating).
Examples of undesirable/unwanted side effects
- Echinacea – more than 20 different types of reactions have been reported, including asthma attacks, loss of pregnancy, hives, swelling, aching muscles and gastrointestinal upsets.
- Feverfew – pregnant women should avoid using this herb, as it can trigger uterine contractions. In animal experiments, the use of feverfew was found to trigger spontaneous abortions (miscarriages).
- Asteraceae plants – which include feverfew, echinacea, dandelion and chamomile. Side effects include allergic dermatitis and hay fever.
- Detailed reference list is located on a separate image page.
- Boseley, Sarah (2006-06-17). "Drugs firm blocks cheap blindness cure". The Guardian. London. Retrieved 2010-05-20.
- Gracer, Richard (February 2007). "The Buprenorphine Effect on Depression" (PDF). naabt.org. National Alliance of Advocates for Buprenorphine Treatment. Retrieved 19 September 2015.
- Bodkin, JA; Zornberg, GL; Lukas, SE; Cole, JO (1995). "Buprenorphine Treatment of Refractory Depression". Journal of Clinical Psychopharmacology. 15: 49–57. doi:10.1097/00004714-199502000-00008. PMID 7714228.
- Mood Stabilizers for Bipolar Disorder (Manic Depressive). Leeheymd.com (2003-08-01). Retrieved on 2011-08-17.
- Wing, DA; Powers, B; Hickok, D (2010). "U.S. Food and Drug Administration Drug Approval: Slow Advances in Obstetric Care in the United States". Obstetrics & Gynecology. 115 (4): 825–33. doi:10.1097/AOG.0b013e3181d53843. PMID 20308845.
- Shen, WW; Mahadevan, J; Hofstatter, L; Sata, LS (July 1983). "Doxepin as a potent H2 and H2 antihistamine for epigastric distress". Am J Psychiatry. 140 (7): 957–8. doi:10.1176/ajp.140.7.957. PMID 6859336.
- Off-label Use of Gabapentin, Idaho Drug Utilization Review, educational leaflet, 2004.
- "Pregnancy". drugs.nmihi.com. (New Medical Information and Health Information). Archived from the original on 11 October 2008.
- Deem, Samuel G. "Premature Ejaculation". Emedicine.com. Retrieved 2011-08-17.
- Gelenberg, Alan J.; et al. (2010). Practice guideline for the treatment of patients with major depressive disorder (PDF). American Psychiatric Association.
- Cheshire, William P.; Fealey, Robert D. (2008). "Drug-induced hyperhidrosis and hypohidrosis: incidence, prevention and management" (PDF). Drug Safety. 31 (2): 109–126. ISSN 0114-5916. PMID 18217788.