The Washington Manual of Medical Therapeutics
- Obeticholic acid (UDCA)
- Obscure gastrointestinal bleeding
- Obstructive lung disease
- Obstructive series
- Obstructive shock
- Obstructive sleep apnea (OSA)
- Occult gastrointestinal bleeding
- Odynophagia
- Ofloxacin
- Ogilvie syndrome
- Olanzapine
- Oligoarthritis
- Oliguric acute kidney injury [table]
- Olmesartan [table]
- Olsalazine, inflammatory bowel disease [table]
- Omadacycline
- Omega-3 fatty acids
- Ophthalmologic examinations, sickle cell disease
- Optic neuritis
- Oral glucose tolerance test (OGTT)
- Oral rehydration solutions
- Organizing pneumonia
- Oritavancin
- Oropharyngeal dysphagia
- Orthostatic hemodynamic changes, gastrointestinal bleeding
- Osmolal gap
- Osmotic diuresis
- Osmotic laxatives
- Osteitis fibrosa cystica
- Osteomalacia
- Osteopenia
- Ototoxicity, aminoglycosides
- Ovarian cancer
- Overnight dexamethasone suppression test
- Overt gastrointestinal bleeding
- Oxazolidinones
- Oxcarbazepine
- Oxygen administration, gastrointestinal bleeding
- Oxygen toxicity