Scientific and medical terms

Clinical trials

Don't confuse adverse events, adverse reactions, adverse effects and side effects.

  • An adverse event is an unwanted event that happens when someone is having treatment, regardless of whether the event is related to the treatment.

  • An adverse reaction is an unwanted reaction that happens when someone is having treatment, which is suspected to be related to the treatment.

  • An adverse effect is an unwanted medical effect directly caused by a treatment.

  • Side effect is more of an umbrella term that is often used in information for the public. It can be used to describe any unintended effect related to treatment.

Data should be considered plural when writing about evidence for NICE guidelines or advice ('These data indicate', 'these data were'). But in wider use, data is generally considered a mass noun (like information). So if you're writing for a more general audience, like in a press release or information for the public, it's fine for data to be singular ('Sometimes anonymised data is used for research purposes').

Use phase I, II, III or IV (that is, roman numerals and a lower case p) when describing phases in clinical trials.

Use confidence interval on first use and abbreviate to CI thereafter. Use 'to' rather than an en dash when describing confidence intervals to avoid confusion with negative numbers ('95% confidence interval –6 to 9').

Report p values with a lower case p and no space between the brackets ('p=0.01'). If a result is quoted as significant but no p value is given, check whether the data are actually statistically significant or whether something like notable might be more accurate.

Use abbreviations for trial names ('RESUSC‑1'). There is no need to write them out in full. Write them in full capital letters: don't capitalise based on what the abbreviation stands for.

Avoid classing people as responders or non-responders when discussing treatment; use 'people whose disease responded' or '…did not respond' instead. In some cases (if, for example, you're describing a lot of data from a complex cancer trial), you may have to use responders and non-responders to avoid long, repetitive sentences.

Method and methodology are not interchangeable. Methodology is a system of methods used in a particular area of study (for example, the Cochrane Review Methodology Database) or the science of methods.

Put a full stop at the end of 'et al.'

Diseases and medical terms

Table 5 Diseases and medical terms: dos and don'ts

Do use

Don't use










Hodgkin lymphoma

Hodgkin's lymphoma







Interferon alfa

Interferon alpha

Hormone-relapsed prostate cancer

Castration-resistant prostate cancer

Magnesium sulfate

Magnesium sulphate

Drugs and medicines

Use generic names for drugs (as listed in the British national formulary) unless a brand name makes more sense in context (for example, in some information for the public). Use lower case for generic names. Always say generic, not non‑branded.

Use medicine if you can. Drugs or medication are fine but if you use drugs make sure that it can't be misinterpreted to mean illegal drugs.

Medicines are given according to a regimen, not a regime.

Dose or dosage: dose refers to the amount of drug ('patients had 500 mg paracetamol' or 'patients had paracetamol 500 mg'; either format is fine but be consistent). Dosage refers to both the amount and frequency of drug ('the recommended dosage is 500 mg, 3 times daily').

Avoid Latin phrases if there are clear English alternatives. If there is no simple English alternative (de novo, vice versa), don't italicise the Latin. Don't use shorthand dosing schedules ('as needed' not p.r.n.; '3 times daily' not t.d.s.).

Italicise Latin names of bacteria and fungi. Italicise virus species, genus and family when used taxonomically ('test for S typhimurium'). Do not italicise a virus name when used generically ('people with any hepatitis virus'). For more information see the Centers for Disease Control and Prevention's guide on scientific nomenclature.