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In recent decades, English has become the lingua franca in all walks of life and (practically) all disciplines, from humanities to life sciences. Though most of us speak and understand it at least to a certain extent, there are always aspects of the language that give us trouble.

Many speakers of English as a second language face difficulties when presented with a regional variety that they are not used to. In this blog post, we will focus on British and American English, but there are many other varieties, too. British and American English began to drift apart intentionally as the countries diverged. If you want to find out more about the differences and how they developed, try linguist Lynne Murphy’s book The Prodigal Tongue.

It is vital to remember that British and American English differ in terms of pronunciation, vocabulary, spelling, punctuation, and usage. In the context of medical/pharmaceutical writing, the key differences lie in spelling, though some also affect terminology. Often, publishers do not mind which of the two varieties you use, but you should use one variety consistently in one text.

This is the first of two articles on differentiating between British and American English. The first article will tackle main spelling differences between the two varieties, focusing on common medical and pharmaceutical terms. The second article will deal with discrepancies in terminology usage. The series should be useful to everyone – regardless of their first language – who needs to compile medical and pharmaceutical documents in English for various purposes in the life sciences industry.


Generally speaking, American English (AmE) has a tendency towards simplification. In AmE terms are written with only one vowel (e.g., “e”) and British English (BrE) with two (e.g., “ae” or “oe”).

1.     “ae” vs. “e”
Common examples of terms that feature this difference are (word order is BrE/AmE):

  • anaemia/anemia
  • haemoglobin/hemoglobin
  • leukaemia/leukemia
  • anaesthetic/anesthetic
  • faeces/feces
  • haemorrhoid/hemorrhoid
  • haemophilia/hemophilia
  • haematotoxicity/hematotoxicity
  • gynaecology/gynecology
  • ischaemic/ischemic
  • caesarean/cesarean [section]
  • orthopaedic/orthopedic
  • paediatric/pediatric
  • synaeresis/syneresis
  • aetiology/etiology

Please note that “aero-” words, such as “aerofoil” and “(an)aerobic,” have the same spelling in both varieties of English.

1.     “oe” vs. “e”
Similarly, vowels “oe” in BrE are replaced by “e” in AmE:

  • diarrhoea/diarrhea
  • coeliac/celiac
  • dyspnoea/dyspnea
  • oedema/edema (and it’s derivative: angio-oedema/angioedema)
  • oesophagus/esophagus
  • oestrogen/estrogen
  • gonorrhoea/gonorrhea
  • menorrhoea/menorrhea
  • homoeopath/homeopath

You may wonder what the situation with the term “foetus/fetus” is. This term is a bit more complex. Both spellings, i.e. “foetus” and “fetus” are acceptable in BrE, while AmE naturally uses “fetus”. However, the BMJ (the British Medical Journal) and most other publications seem to prefer “fetus”. Oxford dictionaries, an authority on BrE, mention “fetus” “is now the standard spelling throughout the English-speaking world, but foetus is still found in British English outside technical contexts.” [1]


Another important difference between the two major variants of English is in word endings. This is true for all main parts of speech: verbs, nouns, and adjectives.

1.     “-our” vs. “-or”
In line with the AmE tendency to simplify, the unstressed BrE “-our” ending is spelled as “-or” in AmE, for example:

  • behaviour/behaviour
  • colour/color
  • tumour/tumor*
  • humour/humor**
  • odour/odor
  • vapour/vapor

* It needs to be noted, though, that “’tumor’ is becoming the standard international spelling in gene and protein names (e.g. tumor necrosis factor).” [2]
** The adjective “humoral” (as defined by the Oxford dictionaries, “relating to the body fluids, especially with regard to immune responses involving antibodies in body fluids as distinct from cells” [3]) has the same spelling in both varieties of English (the spelling “humoural” is incorrect).

2.      “-re” vs. “-er”
Another tiny, but crucial difference (if you want to show off your knowledge of variants of English) is in the unstressed ending “-re”:

  • centre/center
  • fibre/fiber
  • litre/liter
  • metre/meter
  • titre/titer

3.     “-logue” vs. “-log”
The AmE tendency to simplify wherever possible is also clear in the following instances, where the BrE ending “-logue” has morphed over time into the simple “-log”:

  • analogue/analog
  • catalogue/catalog
  • dialogue/dialog
  • homologue/homolog

4.     “-ise” vs. “-ize”
In BrE, for a majority of the verbs ending in “-ise”, the ending “-ize” can also be used. For example, both “stabilise” and “stabilize” are considered correct. However, it is important to choose only one of the forms/endings and use it consistently within a single text to avoid confusion and maintain good style.

In AmE, on the other hand, only the ending “-ize” is considered correct.

Similarly, many words ending in “-lyse” can also be spelled “-lyze” in BrE; to make the matter a bit more complicated, some (including the ones listed below) can only be spelled with “-lyse”. AmE only accepts the “-lyze” spelling:

  • analyse/analyze
  • catalyse/catalyze
  • paralyse/paralyze


In English, the number of exceptions is often just as great as the of items conforming to the rule. In the spirit of this wonderful characteristic, a few other spelling differences between BrE and AmE do not fall under categories above.

For example:

  • aluminium/aluminum (again, tendency of AmE to simplify is quite obvious in this case)
  • intervertebral disc/intervertebral disk
  • leucocyte/leukocyte
  • mould/mold

Next month, we will discuss notable differences between BrE and AmE in terms of terminology. For example, did you know that, depending on the reader’s location, “anaesthesiologist” and “anaesthetist” are considered as two separate professions with vastly different responsibilities?

This article is a compilation of several web sources [4], as well as our own observations during quality assurance steps we perform daily on translations. For more advanced and in-depth advice on medical writing in English, we warmly recommend reading (and consulting while writing) the book Medical Writing: A Prescription for Clarity. It is full of solid and industry-specific language advice, especially on how to get your message across in a clear, concise, and fluent manner.

Furthermore, we at Alamma are always here to help! If you are unsure about your English text and would like an expert proofreader or editor (native in either British or American English) to have a read-through, do not hesitate to send an enquiry to


[1], accessed on 2 Jun 2021
[2], accessed on 3 Jun 2021
[3], accessed on 3 Jun 2021
[4], accessed on 3 Jun 2021