The invention relates to the administration of prescription drug formulary information. A list of drugs that a particular prescription drug plan will pay for in whole or in part is called a formulary. The invention involves the use of information and customizable rules associated with formularies, combined with information from patient medical records, to generate custom, dynamic formularies applicable to specific patients, groups of patients, or both. Depending on the choice of rules and the other information, this may help payers control prescription drug costs by encouraging the use of less-expensive drugs when medically appropriate, but without impairing the freedom of prescribers to prescribe specific drugs according to their professional judgments. Some embodiments may also be adapted to generate and store data about the use and functioning of the embodiments or aspects of them and to generate reports containing some or all such data in response to queries.