| Occipital-frontal circumference |
| OG – infants |
| Oily hair |
| Oily skin |
| Orgasmic dysfunction |
| Osteopathic physician |
| Osteoporosis and aging |
|
| Ostomy – resources |
| Ovarian growths |
| Ovarian mass |
| Over-the-counter birth control |
| Overdose |
| Overeating – resources |
| Oxygen therapy – infants |
|
