01 · Classification
How codeine works
A naturally occurring phenanthrene alkaloid and opioid analgesic/antitussive. About 5% to 10% may be converted by CYP2D6 into morphine; poor and ultra-rapid metabolizers can experience very different effects.
02 · Acute effects
Effects by exposure level
Therapeutic / low
Mild analgesia, reduced coughing, relaxation, drowsiness, constricted pupils, dry mouth, and constipation.
High / non-prescribed
Euphoria, lethargy, slowed reactions, itching, nausea, slurred speech, and heavy sedation.
Severe toxicity
Stupor, respiratory arrest, agonal breathing, cyanosis, severe hypotension, or coma.
Medical emergency
Recognizing opioid overdose
Pinpoint pupils, profound unresponsiveness, slow or absent breathing, gurgling, blue or gray skin, or limp extremities require immediate help.
Call 911. Give naloxone if available, repeat a dose in two to three minutes if normal breathing does not return, provide rescue breathing, and place the person in the recovery position once breathing is restored.
Dangerous combinations
Polydrug interactions
Alcohol, benzodiazepines, other opioids, sedating antihistamines, and sleep aids can compound sedation and respiratory depression.
Never mix opioids with other sedatives or use an unverified pill. Tell emergency responders what may have been taken.
03 · Long-term consequences
Health effects of prolonged heavy use
Variable metabolism
CYP2D6 differences can produce little effect or unexpectedly high morphine exposure and respiratory depression.
Dependence and withdrawal
Repeated use can cause tolerance, body aches, sweating, runny nose, diarrhea, insomnia, and intense cravings after stopping.
Promethazine and dental harm
Sedating syrup combinations can add anticholinergic toxicity, urinary retention, cognitive effects, dry mouth, and tooth decay.
Acetaminophen liver injury
High intake of combination tablets can produce toxic NAPQI accumulation and acute liver failure.
Verified resources
Need help?
SAMHSA National Helpline
1-800-662-4357 · Free, confidential, 24/7 treatment referral and information.
Emergency help
For slow or absent breathing, loss of consciousness, or suspected overdose, call 911 immediately and use naloxone if available.