- Fentanyl is a powerful medication that may have some serious side effects. It may also result in more mild side effects, such as constipation, diarrhea, drowsiness, dizziness, nausea, vomiting, headache, mouth irritation or pain, abdominal pain and fatigue. These side effects apply to all forms of fentanyl. Contact your doctor if these side effects become bothersome.
- Depending on what form of fentanyl you use, you may experience additional side effects. The patch may also cause dry mouth, indigestion, loss of appetite, anxiety, nervousness, redness at the application site, insomnia, sleepiness, sweating and an exaggerated feeling of well-being. If you use the fentanyl lozenge, you may experience difficulty walking, accidental injury, confusion and anxiety, as well as dry mouth, indigestion and itching. The fentanyl tablet may also cause numbness or tingling.
- If you experience severe side effects, go to the emergency room immediately. This includes an allergic reaction (such as facial swelling and hives), as well as extreme dizziness, fainting, hallucinations, muscle rigidity, convulsions, shock, difficulty breathing, extreme drowsiness, difficulty urinating, memory loss, tremors, mouth sores, ulcers, numbness in the extremities, very dry eyes and shortness of breath.
- You will need medical assistance as soon as possible if you've overdosed on fentanyl. Possible signs of an overdose include seizures, cold and clammy skin, low blood pressure, slow heartbeat, slow breathing and extreme drowsiness to the point where you cannot be wakened or cannot respond when spoken to.
- Disclose all of your medical conditions to your doctor before using fentanyl. This list especially includes head injuries, a brain tumor, breathing disorders, seizures, a heart rhythm disorder, mental illness, hypotension, a history of drug addiction, kidney or liver disease, intestinal problems, gallbladder disease, gallstones, an enlarged prostate or pancreatitis. Do not use fentanyl if you are pregnant. If you become pregnant or if you are breastfeeding, discuss this medication with your doctor. Fentanyl can cause withdrawal symptoms in an infant.
- You will not be able to use fentanyl if you have used an MAOI (such as Marplan or Nardil) in the last two weeks, as this could cause potentially fatal side effects. Grapefruit and any grapefruit products can interact with fentanyl. Other drugs that may interact with fentanyl include HIV drugs, antibiotics, verapamil, aprepitant and diltiazem. Talk to your doctor about all medications you are taking, both prescription and non-prescription.