Fentanyl Side Effects

  • Generic Name or Active Ingridient: Fentanyl

Fentanyl is a strong opioid pain reliever, 80 to 100 times more powerful than morphine.

Fentanyl, like all medications, may cause side effects. Many people experience no, or minor, side effects while taking fentanyl. Most side effects are not serious and disappear after a few days. A few side effects are serious and require the immediate attention of a healthcare professional.

Abuse, Dependence and Addiction

Potential for abuse, physical dependence or addiction are possible side effects from taking fentanyl. The U.S. Drug Enforcement Agency, or DEA, categorizes drugs according to their potential for abuse. The DEA has classified fentanyl as a Schedule II narcotic, meaning fentanyl is associated with a high potential for abuse that may lead to mental or physical dependence upon opioids.

Physical dependence to fentanyl means the person will suffer uncomfortable withdrawal symptoms after the level of opioid drops in his system. This sudden drop could be because either the individual has stopped taking fentanyl or he has taken a medication to reduce the amount of fentanyl in his system rapidly. Withdrawal symptoms include:

  • Abdominal Cramps
  • Agitation
  • Anxiety
  • Blurred Vision
  • Insomnia
  • Restlessness
  • Sweating
  • Tremor
  • Vomiting

General Side Effects

The side effects associated with fentanyl are typical of any opioids. These side effects usually become less intense or stop altogether with continued use at proper doses. The most serious side effect associated with fentanyl is breathing problems that may lead to stopped breathing, circulatory problems, dangerously low blood pressure and shock. While many people do not suffer serious side effects while taking Fentanyl, physicians should anticipate side effects in some groups, such as the elderly and very young, and monitor patients accordingly.

The most commonly reported side effects associated with fentanyl are not serious and subside after taking this drug for a few days. Continue taking this medication but contact the prescribing doctor if the following side effects become unbearable or if they do not go away on their own:

  • Anxiety
  • Confusion
  • Depression
  • Dizziness
  • Headache
  • Nausea
  • Rash
  • Sleepiness
  • Trouble Sleeping
  • Vomiting
  • Weakness

Some side effects are serious, requiring immediate help of a medical profession. Discontinue fentanyl immediately and contact a physician if you experience serious side effects, including:

  • Severe Allergic Reactions
  • Blurred Vision or Other Vision Problems
  • Chest Pain
  • Confusion
  • Fainting
  • Fast, Slow or Irregular Heartbeat
  • Hallucinations
  • Mood or Mental Changes Such As Depression)
  • Mouth Sores, Ulcers, Bleeding, or Inflammation
  • Seizure
  • Severe Drowsiness
  • Severe Dry Eyes, Mouth or Skin
  • Severe or Persistent Dizziness or Headache;
  • Severe or Persistent Stomach Pain
  • Shortness of Breath
  • Slow or Shallow Breathing
  • Trouble Urinating
  • Unusual or Severe Weakness or Tiredness

Nervous System

Fentanyl may cause side effects associated with the nervous system, including mental or respiratory depression, especially in elderly patients. Respiratory depression is a condition where the lungs do not adequately exchange oxygen and carbon dioxide, characterized by slow or shallow breathing. Fentanyl may also cause muscle rigidity, especially in the throat near the vocal chords, further complicating respiratory depression. Other nervous system side effects include trouble speaking, stupor, delirium and extreme sleepiness. Individuals taking fentanyl may experience a change in mental state, such as depression, hostility, abnormal thinking, hallucinations or depersonalization.


Cardiovascular side effects associated with fentanyl include severely low blood pressure and slow or irregular heartbeat. While some medical studies suggest fentanyl masks or worsen some heart problems, surgeons routinely use fentanyl for coronary artery surgery.


Gastrointestinal side effects from taking fentanyl in any form include nausea, vomiting and constipation. Digestive side effects include distention, or abdominal swelling. Fentanyl is available in lozenges, spray and soluble film; these forms of fentanyl may cause mouth sores, white patches or sores on the tongue. These products may also be associated with side effects causing dental decay problems, such as cavities, tooth loss and erosion of the gum line.


Respiratory depression is a frequent and serious side effect associated with fentanyl. Coughing, asthma and abnormal breath sounds may be associated with fentanyl. This medication may also cause laryngitis.


Urinary retention or bladder pain is associated with fentanyl use. Consumers have reported decreased libido and ejaculatory difficulties while using a fentanyl patch. One case of the sexual dysfunction, priapism, has been reported.


Fentanyl consumers have reported itching, scaly skin and pustules after using this product. Rashes are associated with fentanyl patch use, typically near the patch application site. Rarely, patients have reported systemic rashes, which cover a large portion of the bodies or erupt in areas not near a patch application site.


Fentanyl is rarely associated with anaphylaxis, a severe and life threatening allergic reaction that affects the entire body. Symptoms of anaphylaxis develop quickly, within minutes or seconds of exposure to fentanyl. Symptoms include abdominal pain, hives, abnormal breathing, confusion, vomiting or diarrhea. Seek professional help immediately if you suspect you or someone you know is experiencing anaphylaxis.


Fentanyl may cause a small amount of hemolysis, which is the breakdown of red blood cells. Hemolysis is most likely due to rapid injections of fentanyl solution, rather than through patches, lozenges or tablets. Practitioners may offset this side effect by slowing the rate of injection or mixing fentanyl into a different solution. Scientists are still working to establish how hemolysis associated with fentanyl impacts a patient's well-being.


Immunologic side effects associated with fentanyl include a case of recurring herpes simplex. Injectable fentanyl may cause other changes in the immune system.


Individuals have reported metabolic side effects associated with fentanyl, including weight loss.

Special Senses

Fentanyl may cause blurred vision.

Body as a Whole

Fentanyl may cause whole-body side effects such as headache, abdominal pain, fatigue, back pain, flu-like symptoms or fever. It may cause edema, or generalized puffiness throughout the body.