Codeine phosphate appears as colorless small crystals or white powder. Odorless. Bitter taste. Solutions are acid to litmus. pH (4% solution) 4.2-5. (NTP, 1992) National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina. CAMEO Chemicals Codeine Phosphate is the phosphate salt of codeine, a naturally occurring phenanthrene alkaloid and opioid agonist with analgesic, antidiarrheal and antitussive activities. Codeine mimics the actions of endogenous opioids by binding to the opioid receptors at many sites within the central nervous system (CNS). Stimulation of mu-subtype opioid receptors results in a decrease in the release of nociceptive neurotransmitters such as substance P, GABA, dopamine, acetylcholine and noradrenaline; in addition, the codeine metabolite morphine induces opening of G-protein-coupled inwardly rectifying potassium (GIRK) channels and blocks the opening of N-type voltage-gated calcium channels, resulting in hyperpolarization and reduced neuronal excitability. Stimulation of gut mu-subtype opioid receptors results in a reduction in intestinal motility and delayed intestinal transit times. Antitussive activity is mediated through codeine’s action on the cough center in the medulla. NCI Thesaurus (NCIt) Codeine Phosphate can cause developmental toxicity according to state or federal government labeling requirements. The CA Office of Environmental Health Hazard Assessment (OEHHA) View More…