| Oxprenolol B2-Adrenergic Vasoconstriction Action Pathway |  | Drug Action | ATP / Potassium cation / Calcium / Magnesium cation / Oxprenolol / Cyclic adenosine monophosphate |
| Oxtriphylline Drug Metabolism |  | Metabolic | Oxtriphylline |
| Oxybuprocaine Action Pathway |  | Drug Action | ATP / Norepinephrine / Oxybuprocaine / Dopamine / Potassium cation / Calcium |
| Oxybutynin Action Pathway |  | Drug Action | Oxybutynin / Calcium / Magnesium cation |
| Oxybutynin Metabolism |  | Metabolic | Oxybutynin / Mesoheme |
| Oxycodone Action Pathway |  | Drug Action | ATP / Norepinephrine / Oxycodone / Dopamine / Potassium cation / Calcium |
| Oxycodone Opioid Agonist Action Pathway |  | Drug Action | ATP / Oxycodone / Calcium / Magnesium cation / Cyclic adenosine monophosphate / gamma-Aminobutyric acid / Pyrophosphoric acid / Sar9, Met (O2)11-Substance P |
| Oxycodone Predicted Metabolism Pathway |  | Metabolic | Oxycodone / Mesoheme |
| Oxymorphone Action Pathway |  | Drug Action | ATP / Norepinephrine / Dopamine / Oxymorphone / Potassium cation / Calcium |
| Oxymorphone Opioid Agonist Action Pathway |  | Drug Action | ATP / Oxymorphone / Calcium / Magnesium cation / Cyclic adenosine monophosphate / gamma-Aminobutyric acid / Pyrophosphoric acid / Sar9, Met (O2)11-Substance P |
| Oxyphenisatin acetate Drug Metabolism |  | Metabolic | Oxyphenisatin acetate |
| Oxyphenonium Action Pathway |  | Drug Action | Oxyphenonium / Calcium / Magnesium cation |
| Oxytetracycline Action Pathway |  | Drug Action | Oxytetracycline |
| Oxytetracycline Anti-bacterial Action Pathway |  | Drug Action | Oxytetracycline |
| Oxytetracycline Drug Metabolism |  | Metabolic | Oxytetracycline |
| Oxytocin Action Pathway |  | Drug Action | Calcium / Magnesium cation |
| Ozanimod Predicted Metabolism Pathway |  | Metabolic | Mesoheme / Ozanimod |
| Paclitaxel Action Pathway |  | Drug Action | Paclitaxel |
| Paclitaxel Action Pathway (old) |  | Drug Action | ATP / Paclitaxel |
| Padeliporfin Drug Metabolism |  | Metabolic | Padeliporfin |
| Pafolacianine Action Pathway |  | Drug Action | Tetrahydrofolic acid / Glutamic acid / NADH / Folic acid / ATP / Magnesium cation / Formic acid / Pafolacianine |
| Paliperidone Dopamine Antagonist Action Pathway |  | Drug Action | Pyridoxal phosphate / Tyrosine / Sapropterin / Dopamine / Levodopa / Paliperidone / Calcium / Iron |
| Paliperidone Serotonin Antagonist Action Pathway |  | Drug Action | Pyridoxal phosphate / Tryptophan / Sapropterin / Paliperidone / Calcium / Iron / Oxitriptan |
| Palivizumab Action Pathway |  | Drug Action | Palivizumab / Magnesium cation |
| Palonosetron Predicted Metabolism Pathway |  | Metabolic | Palonosetron / Mesoheme |