RxList - The Internet Drug Index at http://www.rxlist.com provides a world of information about medicines. The Top 200 Prescriptions list represent nearly 2/3 of all prescriptions filled in the United States . You can perform keyword searches of all RxList monographs (nearly 300 of them) simultaneously for potential drug interactions, side effects and indications. The search engine uses fuzzy logic as well as wildcard searching, just in case your spelling is imperfect. Interestingly, there is now a section on alternative medicines as well, with information on herbs, ayurvedic medicines , Chinese medicines and homeopathic medicines. RxBoard also offers Drug Specific Bulletin Boards for further discussion.

Other sites which are useful if you want more information about drugs include:
Pharminfo at http://www.pharminfo.com , http://www.dmcpharmacy.org/ and http://www.pharmweb.net. The Infomed Drug Guide at http://www.infomed.org/100drugs/ is an excellent compilation of the hundred "essential" drugs a general practitioner needs to be familiar with. It contains critically evaluated information on the selected drugs, which have been chosen in such a way that approximately 90% of all the problems occurring in primary medicine can be dealt with adequately.