Our most comprehensive source for drug information is Lexicomp. It contains complete drug monographs, identification, doses, mechanisms of action, interactions, adverse effects, calculators, patient education, and more.
AHFS Drug Information is a comprehensive, evidence-based source of drug information complete with therapeutic guidelines and off-label uses.
DynaMed offers a medication information for each disease or condition, when applicable, and rates the information according to level of evidence.
Embase is a large biomedical and pharmacological literature database. It encompasses everything published in Medline (PubMed), but has content and indexing favoring drug information.