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. Sometime prior to 2370, they agreed that he'd consult her first, but he broke the promise, coming to the conclusion that he might have Terellian Death Syndrome. After she treated him for his actual problem, Urodelan flu, she added a final reminder to stay away from the database. (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")