- Octreotide, for acromegaly
- Ofloxacin
- Olanzapine, for Alzheimer disease
- Omacetaxine, for chronic leukemia
- Omeprazole (Prilosec)
- Onabotulinum toxin A, for esophageal diverticula
- Ophthalmoscopy
- Opioid antagonist, for narcotic abuse
- Opioids
- Oral contraceptives
- Oral ulcers, in lupus erythematosus
- Orchiectomy
- Organ dysfunction syndrome
- Organ System Involvement in MODS
- Osmolarity
- Osteoarthritis
- Osteomyelitis
- Osteopenia, in hyperparathyroidism
- Osteoporosis
- Osteosarcoma
- Osteotomy
- Ostomy care, after colorectal cancer surgery
- Otitis media
- Ovarian cancer
- Oxacillin
- Oxaliplatin
- Oxazepam, for psychoactive substance abuse
- Oximetry, pulse, in laryngotracheobronchitis
- Oxybutynin chloride, for neurogenic bladder
- Oxycodone, for tendinitis
- Oxygen therapy
- Oxytocin (Pitocin)
Diseases and Disorders