| Obesity | 1 risk assessment, 8 quizzes, 3 calculators |
| Opioid dependence | 1 risk assessment, 1 quiz |
| Optic Neuritis | 3 quizzes |
| Oral Cancer | 1 quiz |
| Orchitis | 2 quizzes |
| Osteoarthritis | 4 quizzes |
| Osteoarthritis of ankle | 2 quizzes |
| Osteoporosis | 3 quizzes |
| Osteosarcoma | 1 quiz |
| Otitic barotrauma | 2 quizzes |
| Otitis externa | 2 quizzes |
| Otitis media with effusion | 3 quizzes |
| Ovarian cancer | 1 risk assessment, 1 quiz |