codeine + magnesium oxide

**Codeine + magnesium oxide** is a fixed-dose combination of the opioid analgesic and antitussive codeine with the antacid and laxative magnesium oxide. Codeine acts primarily as an agonist at **mu-opioid receptors** in the central nervous system, suppressing cough reflex via the medullary cough center and providing mild analgesia, while also reducing intestinal motility that can lead to constipation; it is partially metabolized to morphine via CYP2D6 for enhanced activity. Magnesium oxide neutralizes gastric acid as an antacid and serves as an osmotic laxative to relieve constipation and indigestion. This combination may be used for pain relief with concurrent gastrointestinal symptom management, though pharmacokinetic interactions exist where magnesium oxide can reduce codeine absorption, and it carries risks of opioid dependence, respiratory depression, and constipation.[2][3][8]