| Oligosaccharides | Carbohydrates consisting of between two (DISACCHARIDES) and ten MONOSACCHARIDES connect... more | 34 | 98 | Details |
| Onagraceae | The evening primrose plant family of the order Myrtales, subclass Rosidae, class Magnol... more | 1 | 5 | Details |
| Oncogene Proteins | Proteins coded by oncogenes. They include proteins resulting from the fusion of an onco... more | 3 | 5 | Details |
| Onium Compounds | Ions with the suffix -onium, indicating cations with coordination number 4 of the type ... more | 75 | 259 | Details |
| Ophthalmic Solutions | Sterile solutions that are intended for instillation into the eye. It does not include ... more | 12 | 41 | Details |
| Ophthalmics | Not Available | 17 | 64 | Details |
| Ophthalmological and Otological Preparations | Not Available | 14 | 149 | Details |
| Ophthalmologicals | Not Available | 202 | 1286 | Details |
| Opiate Agonists | Not Available | 18 | 196 | Details |
| Opiate Alkaloids | Alkaloids found in OPIUM from PAPAVER that induce analgesic and narcotic effects by act... more | 48 | 243 | Details |
| Opiate Antagonists | Not Available | 2 | 18 | Details |
| Opiate Partial Agonists | Not Available | 4 | 24 | Details |
| Opioid Agonist | Not Available | 21 | 198 | Details |
| Opioid Agonist/Antagonist | Not Available | 2 | 6 | Details |
| Opioid Anesthetics | Not Available | 6 | 25 | Details |
| Opioid Antagonists | Agents inhibiting the effect of narcotics on the central nervous system. | 21 | 94 | Details |
| Opioid Peptides | The endogenous peptides with opiate-like activity. The three major classes currently re... more | 6 | 19 | Details |
| Opioids | Compounds with activity like OPIATE ALKALOIDS, acting at OPIOID RECEPTORS. Properties i... more | 57 | 328 | Details |
| Opioids, Anilidopiperidine | Not Available | 4 | 23 | Details |
| Opium Alkaloids and Derivatives | Not Available | 10 | 55 | Details |
| Optical Imaging Agent | Not Available | 2 | 8 | Details |
| Oral Hypoglycemics | Oral agents for treating diabetes. | 38 | 267 | Details |
| Orchidaceae | A plant family of the order Asparagales. All members of the orchid family have the same... more | 1 | 1 | Details |
| Orexin receptor agonists | Agonists of orexin receptors used as wakefulness-promoting agents. | 3 | 8 | Details |
| Orexin Receptor Antagonists | Substances that bind to and inhibit the action of OREXIN RECEPTORS. Drugs in this class... more | 3 | 14 | Details |