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Everyone sometimes has to take medicine to keep their bodies functioning properly. This can mean either alleviating symptoms of an underlying condition that is yet to be discovered, or treating an illness. When we take medicines, however, we may not only notice the intended effects, but also other, often unwanted, ones that may be unpleasant or perhaps even dangerous.

Side effect, adverse drug reaction, or adverse event?

Not all negative effects of a particular drug, or medicinal product, are alike. Broadly speaking, they can be divided into two types: side/adverse effects or adverse drug reactions, and adverse events. Though most healthcare professionals are aware of the differences between the two concepts, they are commonly used interchangeably, disregarding the important terminological differences. This is most likely due to the similarity between the expressions and lack of unified use among various sources. It is a true terminological pickle that may perplex the author of a text as to which term to use, and ultimately confuse the end user/reader. All of this may even result in delayed agency procedures, and possible transfer of the terminological issues to the translation.

In an attempt to clarify the above-mentioned terms and make the lives of our clients and translators easier, we at Alamma have turned to the resources made available by the European Medicines Agency (EMA).

EMA defines an adverse event (AE) as “an untoward medical occurrence after exposure to a medicine, which is not necessarily caused by that medicine”. [1] In other words, it is an unpredictable negative reaction that occurs at the time of taking/using a medicinal product, but the reaction may or may not have been caused by the medicinal product itself. AEs are not investigated in clinical studies of specific medicinal products since they are dose- and patient-dependent, i.e., may vary from person to person, depending on the dose taken and the way the product interacts with the body. AEs may also result from prescription errors. There is no way to know if the person taking a medicinal product will experience an AE and the most common way to stop the event is to stop the treatment. All AEs must be reported (by the patient or healthcare professional) to the local pharmacovigilance authorities.

In contrast, an adverse drug reaction (ADR) or simply adverse reaction, sometimes called a side effect or adverse effect, is “response to a medicinal product which is noxious and unintended and which occurs at doses normally used in man for the prophylaxis, diagnosis or therapy of disease or for the restoration, correction or modification of physiological function”. [2] In short, an ADR is a negative reaction that is causally connected to the use of a particular medicinal product at usual doses. [3] ADRs are investigated during clinical studies and drug development processes, and are included in the risk versus benefit analysis. Unexpected adverse reactions, a subset of ADRs, are reactions that are “not consistent with applicable product information or characteristics of drug”. [3] Their name is self-explanatory; such adverse reactions are impossible to predict or expect, since their occurrence has not been included in product information. In light of the definitions stated above, ADRs may be considered a subset of AEs.

The translations

When the terminology in the source language is unclear or confusing, which is often the case due to a large number of (near‑)synonyms for a particular term, translators try to make the translation as clear or even clearer than the source text. In practice this means that the translator will translate synonyms using one single term to make the translation more consistent and understandable.

In this case, could the terms adverse drug reaction, adverse reaction, side effect, and adverse effect be translated using one single term?

If we take a look at the translations of the above-mentioned terms as logged in IATE [4] for a few of the most common European languages, we can see that the situation, and consequently also the translator’s decision, is not as clear-cut.

The table below lists the translations of terms in question into German, Spanish, French, Italian and Slovene. All the listed translations are marked as ‘reliable’*:


adverse eventadverse reactionside effectadverse effect


unerwünschtes Ereignis

Nebenwirkung / negative Auswirkung

unerwünschte Arzneimittelwirkung / Nebenwirkung**

schädigende Wirkung / Schadwirkung / Nebenerscheinung


acontecimiento adverso

reacción adversa***

efecto secundario / efecto colateral

efecto adverso


événement indésirable

réaction indésirable

effet secondaire

effet nocif / effet néfaste


evento avverso

reazione avversa

effetto collaterale

effetto negative / effetto avverso


neželeni dogodek

neželeni učinek

stranski učinek

škodljivi učinek

It is clear from the table above that multiple related terms exist not only in English, but in other languages as well. This inconsistency is most likely due to the near-synonyms in English, which is also the most common source language for EU translations. In all these languages, inconsistencies appear only when speaking about the second group of undesirable effects, the adverse drug reactions. The term adverse event seems to be unproblematic to translate, since only one accepted translation and no synonyms appear in the above languages.

The table above is a good representation of terminological dilemmas translators deal with every day. Each translation is a careful balance between staying faithful to the source text and providing an understandable, clear translation for the target audience. For example, in English, side effect is more likely to be used in texts for patients, and adverse effect for medical professionals. This balance is much more difficult to obtain than it seems at first glance. At Alamma, we do our best to stay up to date with new developments in terminology, while keeping in mind that the translation must primarily be clear, consistent, and, above all, correct. Coupled with our insistence on following clients’ preferences, you can be confident the translations we provide have been prepared with great care and thought.

Have you spotted any other terminological dilemmas in your industry that you think translation agencies should be aware of? Let us know and we will include them onto our checklist!


* Quality indicator ‘reliable’ (indicated by the three stars below the term), denotes terms of highest quality, corroborated by multiple reliable sources.
** The German IATE entry for ‘Nebenwirkung’ notes ‘Nebenwirkung’ and ‘negative Auswirkung’ may be used synonymously.
*** The Spanish IATE entry for ‘reacción adversa’ even states: “Keep in mind that, as stated by F. A. Navarro in their Diccionario de dudas y dificultades de traducción del inglés médico (3rd edition): “in Spanish the expressions ‘efecto adverso’, ‘acontecimiento adverso’, ‘reacción adversa’, ‘efecto secundario’, ‘efecto colateral’ and ‘efecto indeseable’, can be used as synonyms. The most commonly used expressions are, by far, ‘efecto secundario’, ‘efecto adverso’, ‘efecto colateral’ and ‘reacción adversa’’“. (author’s own translation)


[1], accessed 19 Apr 2021[2], accessed 19 Apr 2021[3], accessed 19 Apr 2021[4], accessed 19 Apr 2021