Drug Interaction Checker
Check for interactions between medicines
Add two or more medicines and see the known interactions between them — how serious, why they happen, and what is usually done about it. Plain-English, dose-free, referenced to the BNF, and clear about its limits.
Read this first. This is an educational reference, not a prescribing tool and not a guarantee of safety. It checks a curated list of well-established interactions between the active ingredients on this site — it is not exhaustive and does not include every medicine, herbal remedy, supplement, food, alcohol, or your personal health. A blank result does not mean a combination is safe. Never start or stop a medicine based on this tool — check with your pharmacist or prescriber and the BNF.
Add at least two medicines to check for interactions.
How to read a result
Severity, evidence, and what to do
Each interaction is graded by severity — severe (usually avoided), moderate (used with caution or monitoring) or mild — and carries an evidence note reflecting how well it is documented, mirroring the way the BNF presents interactions. For each one we explain, in plain terms, what can happen, why it happens, and what is usually done about it. What we deliberately don’t do is tell you to change anything: many flagged combinations are prescribed on purpose, with monitoring, because the benefit is worth it. The right response to a flag is to ask your pharmacist or prescriber — not to stop a medicine.
Emergency symptoms. If you or someone else has severe bleeding that won’t stop, difficulty breathing, a very slow or irregular heartbeat, collapse, confusion, or a high fever with muscle stiffness after starting a new medicine, call 999. For urgent advice, call NHS 111.
Related tools
Alongside the interaction checker
Use the Compare Medicines tool to see two or three medicines side by side, the Drug Safety & Side-Effect reference for safety information on a single medicine, and each medicine’s own dose-free guide for its full interaction and monitoring detail. For the principles behind how we source and date this content, see our Quality & Editorial Policy.
Answers
Drug interactions: frequently asked questions
Does "no interactions found" mean the combination is safe?
No — and this is the most important point. This tool checks a curated list of well-established interactions between the active ingredients on this site. It is not exhaustive: it does not cover every medicine, every combination, herbal remedies, supplements, food, alcohol, or your individual health conditions. A blank result means we did not find a listed interaction, not that the combination is safe. Always confirm with your pharmacist or the BNF.
What do the severity levels mean?
They mirror the BNF’s approach. Severe combinations are usually avoided or need specific measures. Moderate ones are used with caution, monitoring or dose adjustment. Mild ones are worth being aware of. Severity is general — how it applies to you depends on your dose, kidneys, liver, age and other medicines.
Does it show doses?
No. Every guide and tool on this site is deliberately dose-free. For doses, and for the definitive interaction detail, use the BNF and the product Summary of Product Characteristics (SmPC).
Can I check a brand name?
Search by the active ingredient (generic) name — for example "warfarin" or "clarithromycin". Brand names are listed within each medicine’s guide.
Should I stop a medicine if the checker flags something?
Never stop a prescribed medicine on the basis of this tool. Some flagged combinations are used deliberately, under monitoring, because the benefit outweighs the risk. Take the result to your pharmacist or prescriber and ask — do not make changes yourself.
How do I report a suspected side effect from a combination?
In the UK, report suspected adverse drug reactions via the MHRA Yellow Card scheme.
Building a formulary or interaction tool?
We build evidence-led, source-labelled interaction and decision-support references for clinical teams — with clear intended-use boundaries.