Starfleet Medical Database or Medical library was 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 USS Enterprise-D chief medical officer Beverly Crusher. (TNG: "Realm of Fear", "Genesis")
In 2375, Seven of Nine consulted this database after experiencing dizziness and double vision. She diagnosed herself as suffering from Albright-Salzman syndrome, a rare condition that hadn't been diagnosed in over two centuries, but The Doctor told her that she was suffering instead from sensory aphasia. (VOY: "Relativity")