Interactions: Information sources

Last updated: Thursday, November 14, 2024


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The SmPCs for medicines are a good starting point to check for interactions. Make sure you check the Contraindications, Special Precautions, Undesirable Effects, and Interactions sections because relevant information may appear in any of these places. Don't rely on the Interactions section alone. 

Some interactions may be listed because they could occur in theory rather than being a proven problem in clinical practice (e.g. where cytochrome p450 is a minor part of a drug's metabolism). Use other sources to differentiate between actual and theoretical concerns. 


Stockley’s Drug Interactions summarises published literature, regulatory statements and product licences, and offers practical advice on patient management. Stockley's Interaction Checker only gives a summary but is helpful for the headline message.

The University of Liverpool run four valuable websites for interactions in therapeutic areas where regimens can be complex. They let you enter all the medicines involved and check for interactions:

The subscription sources Martindale, AHFS Drug Information, or Micromedex can be useful additional resources for interaction enquiries. Lexicomp has a useful section in its drug monographs called 'Metabolism/Transport effects' that includes details of whether a drug is a substrate, inhibitor or inducer of a CYP450 isoenzyme(s). Indiana University also runs a website that has helpful information on whether a drug affects or is affected by CYP450 enzymes.

If you are asked specifically about interactions involving the QT interval the Credible meds site can be helpful. In addition SPS has produced guidance on drug-induced QT prolongation. 

If your enquiry involves an alternative medicine, then you may need to refer to some of the sources listed in that tutorial to help you.

Consider whether professional bodies may have produced guidance on how to manage interactions with drugs used in their speciality (e.g. the European Society of Cardiology’s guide to using NOACs, the Faculty of Sexual and Reproductive Healthcare’s guide to contraceptive interactions). 

Be careful about conducting a general internet search on this subject. If you do, you may like to look at our brief guide to evaluating websites about medicines.

Presenting your answer 

Once you’ve asked sufficient questions, gathered the information required and assessed it, you’ll need to provide an answer. We can offer you some general guidance on answering clinical problems.