Starfleet Medical Database is a nexus of information on diseases and illnesses encountered by Starfleet, including transporter psychosis, Symbalene blood burn and Terellian Death Syndrome. The database was fully searchable via a starship library computer and contained information on both symptoms and treatment. All Starfleet personnel had access to the database.
Lieutenant Reginald Barclay often used the database to self-diagnose himself before consulting a real doctor, much to the dismay of Enterprise-D chief medical officer Beverly Crusher. (TNG: "Realm of Fear," "Genesis")