Get emergency medical help if you have signs of an allergic reaction to a fentanyl patch: hives; chest pain, 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.
Remove the skin patch and call your doctor at once if you have:
slow heart rate, sighing, weak or shallow breathing (up to several days after removing the skin patch);
breathing that stops during sleep;
confusion, severe drowsiness, feeling like you might pass out;
chest pain, fast or pounding heartbeats; 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 overweight, malnourished, or debilitated.
Common fentanyl patch side effects may include:
headache, dizziness, drowsiness, tiredness;
nausea, vomiting, stomach pain, diarrhea, constipation;
itching, redness, or rash where a patch was worn;
sleep problems (insomnia); or
increased sweating, or cold feeling.
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.
 Fentanyl side effects (more detail)
