Niacin

Nitrous Oxide

Novocain

Olestra

Open-Heart Surgery

Ophthalmoscope

Opioid Receptor

Opium

Orthodontics

Oxygen Tent

Pacemaker

Pap Test

Pasteurization

Patent Medicine

Penicillin

Prenatal Diagnostic Techniques

Prenatal Surgery

Quinine

Radial Keratotomy

Radioimmunoassay (RIA)