UK law sets out what that leaflet must contain, and its side-effect words have fixed meanings. This independent guide explains how to read one, quoting the MHRA and the regulations. It does not replace advice from your doctor or pharmacist.
General information only, not medical advice. For advice about your own health, speak to a doctor, pharmacist or other qualified health professional.
DECODE A WORD
What does 'uncommon' mean?
Pick a frequency word from a leaflet to see the band it stands for. The bar shows how often a side effect in that band may happen.
Frequency bands as set out by the MHRA. This is general information about reading leaflets, not medical advice: ask a pharmacist, doctor or NHS 111 about your own medicines.
TWO NUMBERS WORTH KNOWING
From very common to very rare.
The two ends of the scale used on every UK leaflet.
> 1 in 10
Top band on the side-effect scale
A side effect listed as very common may affect more than 1 in 10 people taking the medicine.
VERY COMMON · MHRA
1 in 10,000
Lowest numbered band on the scale
Very rare means it may affect up to 1 in 10,000 people. The MHRA says the classification has no category for rarer events.
VERY RARE · MHRA
The MHRA's annual #MedSafetyWeek runs from 2 to 8 November 2026, its eleventh year, with the theme 'side effects - don't ignore them, report them'.
FOUR THINGS THE SOURCES POINT TO
Using the leaflet, not just keeping it.
None of this is a substitute for talking to a pharmacist or doctor. It is about getting the most from information you already have in the box.
Read it, as the MHRA suggests
The Yellow Card site says to always read the leaflet or instructions, which list known side effects and what to do.
Find a lost leaflet online
The electronic medicines compendium (emc) publishes patient information leaflets that can be viewed and printed.
Check the NHS medicines pages
The NHS Medicines A to Z explains how many common medicines work, how to take them and possible side effects.
Report a suspected side effect
Anyone can report to the Yellow Card scheme. If you are worried about your health, the MHRA points to your doctor, pharmacist or NHS 111.
AI-generated image, not a photograph of a real person or place.
WHAT A LEAFLET MUST COVER
Set out in the regulations.
AI-generated image, not a photograph of a real person or place.
Schedule 27 of the Human Medicines Regulations 2012 lists the contents: the medicine's name, strength and form, what it is for, warnings and interactions, how to use it, what to do about a missed dose or overdose, and possible side effects.
It must also cover the expiry date, storage and ingredients. Regulation 260 says a leaflet must be legible, clear and easy to use, and that target patient groups must be consulted to achieve this.
Questions
Questions people ask
What does 'common' mean on a medicine leaflet?
In the standard frequency categories quoted by the MHRA, 'common' means a side effect may affect up to 1 in 10 people. 'Very common' means more than 1 in 10.
Is 'rare' the same as 'very rare'?
No. Rare means it may affect up to 1 in 1,000 people; very rare means up to 1 in 10,000. 'Not known' means the frequency cannot be estimated from the available data.
Does every medicine come with a leaflet?
The Human Medicines Regulations 2012 say a package leaflet must be included unless all the required information appears on the packaging itself. Registrable homoeopathic products are outside this rule.
Who can report a side effect?
Anyone. The MHRA's Yellow Card scheme accepts reports about medicines, vaccines, medical devices, blood products and e-cigarettes from the public as well as healthcare professionals.
I have lost the leaflet. Where can I find it?
Leaflets for many UK medicines are published on the electronic medicines compendium (emc), where they can be viewed and printed. A pharmacist can also help.
