In medicine, a side effect is an effect of the use of a medicinal drug or other treatment, usually adverse but sometimes beneficial, that is unintended. Herbal and traditional medicines also have side effects.
A drug or procedure usually used for a specific effect may be used specifically because of a beneficial side-effect; this is termed "off-label use" until such use is approved. [1] For instance, X-rays have long been used as an imaging technique; the discovery of their oncolytic capability led to their use in radiotherapy for ablation of malignant tumours.
The World Health Organization and other health organisations characterise the probability of experiencing side effects as: [4] [5]
The European Commission recommends that the list should contain only effects where there is "at least a reasonable possibility" that they are caused by the drug and the frequency "should represent crude incidence rates (and not differences or relative risks calculated against placebo or other comparator)". [6] The frequency describes how often symptoms appear after taking the drug, without assuming that they were necessarily caused by the drug. Both healthcare providers [7] and lay people [8] misinterpret the frequency of side effects as describing the increase in frequency caused by the drug.
Most drugs and procedures have a multitude of reported adverse side effects; the information leaflets provided with virtually all drugs list possible side effects. Beneficial side effects are less common; some examples, in many cases of side-effects that ultimately gained regulatory approval as intended effects, are:
Paroxetine, sold under the brand names Paxil and Seroxat among others, is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. It is used to treat major depressive disorder, obsessive-compulsive disorder, panic disorder, social anxiety disorder, post-traumatic stress disorder, generalized anxiety disorder, and premenstrual dysphoric disorder. It has also been used in the treatment of premature ejaculation and hot flashes due to menopause. It is taken orally.
Quetiapine, sold under the brand name Seroquel among others, is an atypical antipsychotic medication used for the treatment of schizophrenia, bipolar disorder, and major depressive disorder. Despite being widely used as a sleep aid due to its sedating effect, the benefits of such use may not outweigh its undesirable side effects. It is taken orally.
Bupropion, formerly called amfebutamone, and sold under the brand name Wellbutrin among others, is an atypical antidepressant primarily used to treat major depressive disorder and to support smoking cessation. It is also popular as an add-on medication in the cases of "incomplete response" to the first-line selective serotonin reuptake inhibitor (SSRI) antidepressant. Bupropion has several features that distinguish it from other antidepressants: it does not usually cause sexual dysfunction, it is not associated with weight gain and sleepiness, and it is more effective than SSRIs at improving symptoms of hypersomnia and fatigue. Bupropion, particularly the immediate release formulation, carries a higher risk of seizure than many other antidepressants, hence caution is recommended in patients with a history of seizure disorder. The medication is taken by mouth.
Levetiracetam, sold under the brand name Keppra among others, is a medication used to treat epilepsy. It is used for partial-onset, myoclonic, or tonic–clonic seizures and is taken either by mouth as an immediate or extended release formulation or by injection into a vein.
Buprenorphine, sold under the brand name Subutex among others, is an opioid used to treat opioid use disorder, acute pain, and chronic pain. It can be used under the tongue (sublingual), in the cheek (buccal), by injection, as a skin patch (transdermal), or as an implant. For opioid use disorder, the patient must have moderate opioid withdrawal symptoms before buprenorphine can be administered under direct observation of a health-care provider.
Fexofenadine, sold under the brand name Allegra among others, is an antihistamine pharmaceutical drug used in the treatment of allergy symptoms, such as hay fever and urticaria.
Doxepin is a medication belonging to the tricyclic antidepressant (TCA) class of drugs used to treat major depressive disorder, anxiety disorders, chronic hives, and insomnia. For hives it is a less preferred alternative to antihistamines. It has a mild to moderate benefit for sleeping problems. It is used as a cream for itchiness due to atopic dermatitis or lichen simplex chronicus.
Betahistine, sold under the brand name Serc among others, is an anti-vertigo medication. It is commonly prescribed for balance disorders or to alleviate vertigo symptoms. It was first registered in Europe in 1970 for the treatment of Ménière's disease, but current evidence does not support its efficacy in treating it.
Biperiden, sold under the brand name Akineton among others, is a medication used to treat Parkinson disease, certain drug-induced movement disorders and Tourette Syndrome. It is not recommended for tardive dyskinesias. It is taken by mouth, injection into a vein, or muscle.
Azelastine, sold under the brand name Astelin among others, is a H1 receptor-blocking medication primarily used as a nasal spray to treat allergic rhinitis (hay fever) and as eye drops for allergic conjunctivitis. Other uses may include asthma and skin rashes for which it is taken by mouth. Onset of effects is within minutes when used in the eyes and within an hour when used in the nose. Effects last for up to 12 hours.
Desvenlafaxine, sold under the brand name Pristiq among others, is a medication used to treat depression. It is an antidepressant of the serotonin-norepinephrine reuptake inhibitor (SNRI) class and is taken by mouth. It is recommended that the need for further treatment be occasionally reassessed. It may be less effective than its parent compound venlafaxine, although some studies have found comparable efficacy.
Asenapine, sold under the brand name Saphris among others, is an atypical antipsychotic medication used to treat schizophrenia and acute mania associated with bipolar disorder as well as the medium to long-term management of bipolar disorder.
Olanzapine/fluoxetine is a fixed-dose combination medication containing olanzapine (Zyprexa), an atypical antipsychotic, and fluoxetine (Prozac), a selective serotonin reuptake inhibitor (SSRI). Olanzapine/fluoxetine is primarily used to treat the depressive episodes of bipolar I disorder as well as treatment-resistant depression.
Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic drug that can be bought without a prescription and provides relief from nasal congestion, sneezing, or hives caused by pollen, dust mites, or animal allergy with few side effects. Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. Consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use.
Lurasidone, sold under the brand name Latuda among others, is an antipsychotic medication used to treat schizophrenia and bipolar disorder. It is taken by mouth.
Women should speak to their doctor or healthcare professional before starting or stopping any medications while pregnant. Non-essential drugs and medications should be avoided while pregnant. Tobacco, alcohol, marijuana, and illicit drug use while pregnant may be dangerous for the unborn baby and may lead to severe health problems and/or birth defects. Even small amounts of alcohol, tobacco, and marijuana have not been proven to be safe when taken while pregnant. In some cases, for example, if the mother has epilepsy or diabetes, the risk of stopping a medication may be worse than risks associated with taking the medication while pregnant. The mother's healthcare professional will help make these decisions about the safest way to protect the health of both the mother and unborn child. In addition to medications and substances, some dietary supplements are important for a healthy pregnancy, however, others may cause harm to the unborn child.
Buprenorphine/naloxone, sold under the brand name Suboxone among others, is a fixed-dose combination medication that includes buprenorphine and naloxone. It is used to treat opioid use disorder, and reduces the mortality of opioid use disorder by 50%. It relieves cravings to use and withdrawal symptoms. Buprenorphine/naloxone is available for use in two different forms, under the tongue or in the cheek.
Somnifacient, also known as sedatives or sleeping pills, is a class of medications that induces sleep. It is mainly used for treatment of insomnia. Examples of somnifacients include benzodiazepines, barbiturates and antihistamines.
Anti-allergic agents are medications used to treat allergic reactions. Anti-allergic agents have existed since 3000 B.C in countries such as China and Egypt. It was not until 1933 when antihistamines, the first type of anti-allergic agents, were developed. Common allergic diseases include allergic rhinitis, allergic asthma and atopic dermatitis with varying symptoms, including runny nose, watery eyes, itchiness, coughing, and shortness of breath. More than one-third of the world's population is currently being affected by one or more allergic conditions.