- ophthalmoscope
- opiate
- opioid
- opioid growth factor
- opium tincture
- opportunistic infection
- oprelvekin
- OPT-80
- optic chiasm
- optic chiasma
- optic nerve
- optic pathway glioma
- optic tract
- optical coherence tomography
- optical spectroscopy
- optimism
- Optison
- Ora-Testryl
- Oracit
- oral
- oral and maxillofacial surgeon
- oral cancer
- oral cavity
- oral cavity cancer
- oral contraceptive pill
- oral fludarabine phosphate
- oral Hsp90 inhibitor IPI-493
- oral JAK inhibitor INCB18424
- oral JAK2 inhibitor SB1518
- oral microencapsulated diindolylmethane
- oral milataxel
- oral picoplatin
- oral sodium phenylbutyrate
- oral surgeon
- oral topotecan hydrochloride
- Oralet
- Oramorph
- Oramorph SR
- Orasone
- Orathecin
- Orazol
- orchidectomy
- orchiectomy
- oregovomab
- Orestralyn
- organ
- organelle
- organic food
- organism
- orgasm