Side effect

The World Health Organization and other health organisations characterise the probability or chance of experiencing side effects as:[2][3]

• Very common, ≥ ¹⁄₁₀
• Common (frequent), ¹⁄₁₀ to ¹⁄₁₀₀
• Uncommon (infrequent), ¹⁄₁₀₀ to ¹⁄₁₀₀₀
• Rare, ¹⁄₁₀₀₀ to ¹⁄₁₀₀₀₀
• Very rare, < ¹⁄₁₀₀₀₀

The European Commission recommends that the list should contain only effects where "at least a reasonable possibility" exists that it is caused by the drug and the frequency "should represent crude incidence rates (and not differences or relative risks calculated against placebo or other comparator)".[4] That is, the frequency describes how often symptoms appear after taking the drug, not caused by the drug. Both health care providers[5] and lay people[6] misinterpret the frequency of side effects as describing the increase in frequency caused by the drug.

Possible side effects of nicotine.[7][8]

• 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.[9]
• Buprenorphine has been shown experimentally (1982–1995) to be effective against severe, refractory depression.[10][11]
• 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.[12]
• Dexamethasone and betamethasone in premature labor, to enhance pulmonary maturation of the fetus.[13]
• Doxepin has been used to treat angioedema and severe allergic reactions due to its strong antihistamine properties.[14]
• 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.[15]
• Hydroxyzine, an antihistamine, is also used as an anxiolytic.
• Magnesium sulfate in obstetrics for premature labor and preeclampsia.[13]
• Methotrexate (MTX), approved for the treatment of choriocarcinoma, is frequently used for the medical treatment of an unruptured ectopic pregnancy.[16]
• 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.[17]
• 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).[18][19]

• Echinacea – more than 20 different types of reactions have been reported, including asthma attacks, loss of pregnancy, hives, swelling, aching muscles and gastrointestinal upsets.[20]
• Feverfew – pregnant women should avoid using this herb, as it can trigger uterine contractions which could lead to premature labour or miscarriage.[21]
• 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

• "MedEffect Canada". Health Canada.
• "Definitions" (PDF). World Health Organisation.

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