Glossary of medicine terms

Contraindication, excipient, POM, controlled drug… Patient leaflets and medicine facts are full of technical words. Here we explain them simply, in a few sentences each. For a particular medicine, always read its own leaflet. How a leaflet is organised is explained in How to read a patient leaflet.

A B C D E G I M P R S Y

Active substance (active ingredient): The part of a medicine that makes it work – for example paracetamol. Everything else in the medicine is an excipient. The generic name of a medicine is the name of its active substance (for example “paracetamol”).
Additional monitoring (▼): A black triangle pointing down (▼) in the leaflet and the SmPC means that the medicine is being monitored even more closely for safety. This is usually because it contains a new active substance or is a new biological medicine. The monitoring typically lasts for the first 5 years after approval. It does not mean the medicine is unsafe. Report any suspected side effect to the Yellow Card scheme.
Adverse reaction: The medical term for a side effect: a harmful and unintended response to a medicine.
ATC code: A code of up to 7 characters from the international ATC classification. It sorts active substances by the organ or body system they act on and by how they work. For example, N02BE01 is paracetamol. More in How to read ATC codes.
Bioequivalence: Proof that a generic gives comparable levels of the active substance in the blood to the original medicine. The company usually shows this in studies. It is one of the conditions for licensing a generic.
Biosimilar: A biological medicine that is highly similar to another biological medicine that is already licensed. Biological medicines are made from, or come from, a biological source – for example insulin. A biosimilar is not a generic, because complex biological molecules cannot be made exactly the same. A pharmacist must not swap a biological medicine without asking the prescriber.
BNF: BNF stands for British National Formulary. The BNF code in the facts box shows the chapter, section and paragraph of the BNF that the medicine belongs to.
Contraindication: A reason not to use a medicine – for example an allergy to one of its ingredients or a particular illness. In most leaflets you will find contraindications in section 2, for example under “Do not take …” or “You should not be given …”.
Controlled drug: A medicine that the law controls more strictly because it can be misused or cause dependence, for example morphine, tramadol or diazepam. The Misuse of Drugs Regulations 2001 divide controlled drugs into five schedules (Northern Ireland has its own regulations). Schedule 1 has the strictest rules and schedule 5 the least strict. A prescription for a schedule 2, 3 or 4 medicine is valid for 28 days.
dm+d (NHS Dictionary of Medicines and Devices): The NHS standard dictionary of medicines and medical devices. Each medicine or device has a code. The NHS Business Services Authority runs it. It describes medicines at several levels – for example the general medicine (“Atenolol 100 mg tablets”) and the product of one supplier. Many facts on this site come from it. It does not show what is in stock.
Dose: How much of a medicine to take at one time, how often and for how long. In most leaflets the usual dose is in section 3.
Excipient: Any ingredient of a medicine other than the active substance – for example fillers, colourings, preservatives or the tablet coating. Most have no effect of their own. A few have a known effect for some people (for example lactose or sodium). The leaflet then mentions them in section 2. All excipients are listed in section 6.
Expiry date (EXP): The date after which you should not use the medicine. It is printed on the pack as a month and a year, usually after “EXP”. The leaflet usually says that the expiry date refers to the last day of that month. The leaflet also tells you how to store the medicine and, for some medicines, how long you can use it after opening.
General sale list medicine (GSL): A medicine you can buy without a prescription, in pharmacies and also in other shops such as supermarkets. Some general sale medicines, for example paracetamol tablets, can only be sold in small packs outside a pharmacy.
Generic medicine: A medicine with the same active substance in the same pharmaceutical form as the original medicine. Its bioequivalence has been shown. It can be sold only after the original medicine’s period of protection has ended. It may differ in name, appearance and excipients. More in Brand-name and generic medicines.
Indication: What a medicine is approved to treat or prevent. In most leaflets you will find it in section 1.
Interaction: When another medicine, food or drink (for example alcohol) changes the effect of a medicine. Tell your doctor or pharmacist about all the medicines you take, including those bought without a prescription. In most leaflets, interactions are in section 2.
Marketing authorisation: The licence that allows a medicine to be sold. In the UK, the MHRA grants it. The MHRA approves the leaflet as part of the licence. The licence number starts with letters such as PL – see PL number.
Marketing authorisation holder: The company that holds the licence for a medicine and is responsible for it. Its name and address are in section 6 of the leaflet. It may be different from the manufacturer.
MHRA: The Medicines and Healthcare products Regulatory Agency, the organisation that regulates medicines in the UK. It licenses medicines, approves their leaflets, runs the Yellow Card scheme and publishes leaflets and SmPCs on its Products website.
Parallel import: A medicine licensed in a country of the European Economic Area (the EU countries, Iceland, Liechtenstein and Norway) that an importer brings in and sells in the UK. The importer needs a parallel import licence (PLPI) from the MHRA. The medicine must work in the same way as the UK product, but the pack may be relabelled or repackaged.
Patient leaflet (patient information leaflet, PIL): The leaflet in the medicine pack, written for the person taking the medicine. It is based on the SmPC and approved by the MHRA. The law sets out what it must contain and in which order.
Pharmaceutical form: The form in which a medicine is made – for example film-coated tablet, capsule, oral solution, cream or injection.
Pharmacy medicine (P): A medicine you can buy without a prescription, but only in a pharmacy and under a pharmacist’s supervision.
PL number: The number of a UK marketing authorisation, printed on the pack and in the leaflet. PL means a licence for the whole UK. PLGB is an older licence for Great Britain; since 1 January 2025 it is valid for the whole UK too. PLNI is for Northern Ireland only. PLPI is a parallel import licence.
Prescription-only medicine (POM): A medicine you can only get with a prescription from a doctor or another authorised health professional. A pharmacy or another licensed place supplies it. New medicines are usually prescription-only at first.
Prescription charge: In England you pay a charge for each item on an NHS prescription, unless you are exempt (you do not have to pay). For example, people under 16 or aged 60 or over are exempt. A prescription prepayment certificate (PPC) covers all your NHS prescriptions for 3 or 12 months for a fixed price. NHS prescriptions dispensed in Scotland, Wales and Northern Ireland are free. Special rules apply to prescriptions issued in another part of the UK.
Route of administration: How a medicine is given – for example oral (by mouth), cutaneous (on the skin), inhalation or intravenous (into a vein).
Serious Shortage Protocol (SSP): A set of rules that health ministers can issue when there is a serious shortage of a medicine. It lets a pharmacist supply an alternative named in the protocol – for example another strength or form – without a new prescription. The pharmacist must think the alternative is suitable for you, and you must agree.
Shelf life: How long a medicine can be used if the pack is unopened, for example 3 years. The expiry date on the pack shows when this ends.
Side effect: An unwanted effect of a medicine. Not everybody gets side effects. In most leaflets, section 4 lists them by seriousness and by how often they happen. For example, a “rare” side effect may affect up to 1 in 1,000 people.
SmPC (Summary of Product Characteristics): A description of a medicine’s properties and how to use and prescribe it, written for doctors, nurses and pharmacists. The patient leaflet is based on it.
Strength: How much active substance is in one tablet, capsule or dose – for example 500 mg, or 250 mg in 5 ml of a liquid.
Yellow Card scheme: The MHRA scheme for reporting suspected side effects and other problems with medicines. Anyone can report, on the Yellow Card website or in the free app. You can also report for someone you care for. You do not need to be sure that the medicine caused the problem.

More guides: How to read a patient leaflet · Medicine facts explained · Brand-name and generic medicines · How to read ATC codes

Sources

We based this page on these documents and checked the facts against them on 4 November 2026. For each one we say what we took from it.

The Human Medicines Regulations 2012, regulation 8 (interpretation) – active substance, excipient, adverse reaction (“noxious and unintended”), package leaflet, UK marketing authorisation.
The Human Medicines Regulations 2012, regulation 260 – the leaflet follows the SmPC and the order of Schedule 27; Schedule 27 – contents of the leaflet: indications, contraindications, interactions with medicines, alcohol and food, excipients that matter for safe use, dose, side effects, expiry date and storage, the licence holder and manufacturer; Schedule 24 – the expiry date on the pack as month and year.
Patient leaflets on this site, for example Bonviva and Daptomycin – the numbered sections (indication in section 1, “Do not take” (Bonviva) and “You should not be given” (Daptomycin) in section 2, dose in section 3, side effects in section 4, contents in section 6), “Rare (may affect up to 1 in 1,000 people)”, the expiry date referring to the last day of the month.
MHRA public assessment report, glossary (PDF) – contraindication (“any factor that makes it unwise to give a particular medicine to a patient”), interaction (effects changed by food or other medicines).
MHRA: Find product information about medicines – the SmPC and the patient leaflet, which is based on it; additional monitoring typically for new active substances and new biologicals for 5 years.
MHRA: The Yellow Card scheme – guidance – the black triangle, reporting through the website and the app, a suspicion is enough; Yellow Card – anyone can report; NHS: Medicines information – reports on behalf of someone you are caring for.
MHRA: reclassification guidance (PDF) – POM, P and GSL; new medicines usually start as POM; Human Medicines Regulations 2012, Schedule 15 – small packs of paracetamol on general sale.
The Misuse of Drugs Regulations 2001 – the five schedules (morphine in schedule 2, tramadol in schedule 3, diazepam in schedule 4) and the 28-day validity of prescriptions (regulation 16); The Misuse of Drugs Regulations (Northern Ireland) 2002.
NHSBSA: NHS Dictionary of Medicines and Devices (dm+d) and the dm+d data model (DOCX) – what the dm+d is, its levels (“Atenolol 100 mg tablets”), BNF and ATC codes; dm+d editorial policy (DOCX) – a discontinued pack may still be in the supply chain; a generic is bioequivalent to the reference product, shown by bioavailability studies (comparable blood levels); NHSBSA: Prescription Services glossary (DOCX) – the BNF code shows the chapter, section and paragraph.
MHRA: Types of application (legal basis) – generic medicines: same active substance and pharmaceutical form, bioequivalent; MHRA: Guidance on the licensing of biosimilar products – biosimilars, no substitution in the pharmacy without the prescriber; NHS Specialist Pharmacy Service: Understanding biological and biosimilar medicines – biological medicines and biosimilars.
NHS: Medicines information – the generic name is the name of the active ingredient.
World Health Organization: ATC classification – the international ATC classification; N02BE01 paracetamol.
NHS Specialist Pharmacy Service: Understanding excipients in medicines – excipients, most have no effect, some have a known effect.
MHRA: Apply for a licence to market a medicine in the UK and Supplying authorised medicines to Northern Ireland – the PL, PLGB and PLNI prefixes; MHRA: Apply for a parallel import licence – parallel imports with no therapeutic difference from the UK product, PLPI; GOV.UK: Countries in the EU and EEA – the EEA countries.
MHRA: Medicines: packaging, labelling and patient information leaflets – the MHRA approves the leaflet; MHRA: Best practice guidance on patient information leaflets – side effects by seriousness and frequency.
The Human Medicines Regulations 2012, regulation 226A – Serious Shortage Protocols issued by the Ministers; NHSBSA: Serious Shortage Protocols – the patient has to agree.
NHS prescription charges: nhs.uk (England), NHS inform (Scotland), GOV.WALES (Wales), nidirect (Northern Ireland); NHS: prescription prepayment certificate – 3-month and 12-month certificates; NHSBSA leaflet HC12 (PDF) – who does not have to pay.

This glossary explains the general meaning of terms and does not replace advice from a doctor or pharmacist. Last updated 4 November 2026. Found a mistake? Email us at info@patient-info.co.uk.