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. Developing drugs is a complicated process, because no two people are exactly the same, so even drugs that have virtually no side effects, might be difficult for some people. Also, it is difficult to make a drug that targets one part of the body but that does not affect other parts, the fact that increases the risk of side effects in the untargeted parts.
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 to 1⁄10
- Uncommon (infrequent), 1⁄1000 to 1⁄100
- Rare, 1⁄10000 to 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 angioedema 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 which could lead to premature labour or miscarriage.
- Asteraceae plants – which include feverfew, echinacea, dandelion and chamomile. Side effects include allergic dermatitis and hay fever.
- Paradoxical reaction, an effect of a substance opposite to what would usually be expected.
- Pharmacogenetics, the use of genetic information to determine which type of drugs will work best for a patient
- "Why do side effects occur? | Guides | HIV i-Base". i-base.info.
- "Common and Rare Side Effects for misoprostol oral".
- "Archived copy" (PDF). Archived (PDF) from the original on 4 March 2016. Retrieved 29 April 2016.CS1 maint: archived copy as title (link)
- Detailed reference list is located on a separate image page.
- Boseley, Sarah (17 June 2006). "Drugs firm blocks cheap blindness cure". The Guardian. London. Retrieved 20 May 2010.
- 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 (1): 49–57. doi:10.1097/00004714-199502000-00008. PMID 7714228.
- Mood Stabilizers for Bipolar Disorder (Manic Depressive) Archived 13 November 2011 at the Wayback Machine. 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. Archived from the original on 4 September 2011.
- Off-label Use of Gabapentin Archived 9 August 2007 at the Wayback Machine, 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. Archived from the original on 1 December 2008. Retrieved 17 August 2011.
- 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. doi:10.2165/00002018-200831020-00002. ISSN 0114-5916. PMID 18217788. S2CID 23041000.
- "Filagra Vs Fildena". Filagra100mg.com. 23 February 2017. Archived from the original on 3 July 2017.
- Wells, Rebecca Erwin; Turner, Dana P.; Lee, Michelle; Bishop, Laura; Strauss, Lauren (1 April 2016). "Managing Migraine During Pregnancy and Lactation". Current Neurology and Neuroscience Reports. 16 (4): 40. doi:10.1007/s11910-016-0634-9. ISSN 1528-4042. PMID 27002079. S2CID 10098257.