Info sources: Interactions
See our problem solving page about this subject for more information.
EMC – the SmPCs for medicines describe their Interactions (in section 4.5 of each SmPC).
BNF online – basic info about interactions. Type drug name, then scroll down the page to the Interactions section.
Drugs.com – has a free interaction checker; type each drug one at a time and then click 'Add'.
Medscape – free interactions checker. Type a drug name, select it from a drop-down list, then add a second drug.
Specialist websites – for interactions involving cancer medicines, HIV medicines, viral hepatitis medicines, antifungal medicines, and Covid-19 medicines.