BNF
BNF Publications app gives you up-to-date offline access to the British National Formulary (BNF) and the British National Formulary for Children (BNFC). The app provides information on selection of safe and effective medication for individual patients.
Download app: free from your app store 
Information access: free access to medical information
Epocrates
Epocrates Plus is a drug app that allows you to review drug prescribing and safety information for thousands of brands and OTC drugs. The app provides a function for checking potentially harmful drug-drug interactions among up to 30 drugs at a time, identify pills by imprint code and physical characteristics and more
Download app: free from your app store 
Information access: free access to some content. Additional information available through individual subscription.
MedScape
The free medical app from MedScape (medscape.com) includes drug reference tool and a drug interaction checker to use in clinical settings.
Download app: free from your app store
Information access: free access to medical information
Skyscape includes over 400 dosing and clinical calculators as well as evidence-based clinical information on hundreds of diseases and symptom-related topics.
Download app: free from your app store
Information access: free access to part of the content with possibility to additional in- app purchase