Get emergency medical help if you have signs of an allergic reaction to Ultracet: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
In rare cases, acetaminophen may cause a severe skin reaction that can be fatal. This could occur even if you have taken acetaminophen in the past and had no reaction. Stop taking this medicine and call your doctor right away if you have skin redness or a rash that spreads and causes blistering and peeling.
This 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:
noisy breathing, sighing, shallow breathing, breathing that stops during sleep;
a slow heart rate or weak pulse;
a light-headed feeling, like you might pass out;
seizure (convulsions);
chest pain;
liver problems - upper stomach pain, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);
low cortisol levels - nausea, vomiting, loss of appetite, dizziness, worsening tiredness or weakness; or
high levels of serotonin in the body - agitation, hallucinations, fever, sweating, shivering, fast heart rate, muscle stiffness, twitching, loss of coordination, nausea, vomiting, diarrhea.
Serious breathing problems may be more likely in older adults and in those who are debilitated or have wasting syndrome or chronic breathing disorders.
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 Ultracet side effects may include:
dizziness, drowsiness;
stomach pain, nausea, loss of appetite;
diarrhea, constipation; 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.
 Ultracet side effects (more detail)
