Get emergency medical help if you have signs of an allergic reaction to Demerol: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Opioid medicine can slow or stop your breathing, and death may occur. A person caring for you should seek emergency medical attention if you have slow breathing with long pauses, blue colored lips, or if you are hard to wake up.
Stop using this medicine and call your doctor at once if you have:
slow heartbeats, weak or shallow breathing, breathing that stops during sleep;
severe drowsiness, feeling like you might pass out;
confusion, mood changes;
severe constipation;
tremors, muscle movements you cannot control, or a seizure (convulsions); or
low cortisol levels - nausea, vomiting, loss of appetite, dizziness, worsening tiredness or weakness.
Seek medical attention right away if you have symptoms of serotonin syndrome, such as: agitation, hallucinations, fever, sweating, shivering, fast heart rate, muscle stiffness, twitching, loss of coordination, nausea, vomiting, or diarrhea.
Serious side effects may be more likely in older adults and those who are malnourished or debilitated.
Long-term use of opioid medication may affect fertility (ability to have children) in men or women. It is not known whether opioid effects on fertility are permanent.
Common Demerol side effects may include:
dizziness, drowsiness;
headache;
nausea, vomiting; or
sweating.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Demerol side effects (more detail)
