Lexicomp combines several different pharmacology and toxicology resources into a single searchable interface. Topics include interactions between drugs, evaluations of drugs, toxicity of common substances, herbal preparations, calculation of dosage, etc.
While basic PubMed is free to all Internet users, this link adds blue "Jefferson" buttons to individual citations that connect to Jefferson journal subscriptions and document delivery services for full-text options.
PubMed is the National Library of Medicine's own interface for MEDLINE and also includes PREMEDLINE (new citations which don't have their subject headings yet) and OLDMEDLINE (reaching back to the 1950s). Use it to identify journal articles on your biomedical topic.
Scopus is Scott Memorial Library's broadest literature database for nursing, life and health sciences. Scopus searches citations and abstracts of over 19,000 journals across a broad spectrum of sciences, medicine, social sciences and technology, science-related Web sites, conference papers, and world patent literature. Alerts and individual profiles are available. Since 1996, Scopus has indexed the citations and references for each document, making it possible to track citations to individual documents and authors.