Side effect

Key takeaways

Side effect belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Side effect to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Side effect from memory before moving on to harder problems.

Reference excerpt

In medicine, a side effect is an unintended effect caused by a medicinal drug or other treatment's capacities or properties, and these effects are often adverse but sometimes beneficial. 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. 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.

Frequency of side effects

The World Health Organization and other health organisations characterise the probability of experiencing side effects as:

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 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)". The frequency describes how often symptoms appear after taking the drug, without assuming that they were necessarily caused by the drug. Both healthcare providers and lay people misinterpret the frequency of side effects as describing the increase in frequency caused by the drug.

Examples of therapeutic side effects

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:

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, also helps smoking cessation; this indication was later approved, and the name of the drug as sold for smoking cessation is Zyban. Bupropion branded as Zyban may be sold at a higher price than as Wellbutrin, so some physicians prescribe Wellbutrin for smoking cessation. 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 disorder, 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 sexual climax in men, and can be used to treat premature ejaculation. Sildenafil was originally intended for pulmonary hypertension; subsequently, it was discovered that it also produces erections, for which it was later approved. 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). Thalidomide, a drug sold over the counter from 1957 to 1961 as a tranquiliser and treatment for morning sickness of pregnancy, became notorious for causing tens of thousands of babies to be born without limbs and with other conditions, or stillborn. The drug, though still subject to other adverse side-effects, is now used to treat cancers and skin disorders, and is on the World Health Organization's List of Essential Medicines.

See also Adverse drug reaction (ADR), a harmful unintended result caused by taking medication Combined drug intoxication Conservative management Drug-drug interaction (DDI), an alteration of the action of a drug caused by the administration of other drugs Iatrogenesis 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 Unintended consequences

References

External links "MedEffect Canada". Health Canada. 13 July 2011. "Definitions" (PDF). World Health Organization.

Worked examples

Example 1 — a first encounter with Side effect

Start with the simplest possible case. Write down what Side effect claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Side effect before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Side effect ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Side effect

In research: Side effect appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Side effect in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Side effect is common in secondary-school and first-year university syllabi. It links to neighbouring topics Clinical pharmacology, so understanding it makes those chapters shorter.
In everyday life: Look for Side effect outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Side effect in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Side effect means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Side effect out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Side effect in simple terms?

In medicine, a side effect is an unintended effect caused by a medicinal drug or other treatment's capacities or properties, and these effects are often adverse but sometimes beneficial. Herbal and traditional medicines also have side effects.

Why does Side effect matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Side effect?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Side effect.