Subsys Side Effects

Generic Name: fentanyl

Note: This page contains side effects data for the generic drug fentanyl. It is possible that some of the dosage forms included below may not apply to the brand name Subsys.

It is possible that some side effects of Subsys may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to fentanyl: film, lozenge/troche, spray, tablet

As well as its needed effects, fentanyl (the active ingredient contained in Subsys) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking fentanyl, check with your doctor immediately:

More common
  • Black, tarry stools
  • blurred vision
  • chest pain
  • confusion
  • convulsions
  • cough
  • decreased urine
  • difficult or labored breathing
  • dizziness
  • dry mouth
  • fainting
  • fever or chills
  • increased thirst
  • irregular heartbeat
  • lightheadedness
  • loss of appetite
  • lower back or side pain
  • mood changes
  • muscle pain or cramps
  • nausea or vomiting
  • nervousness
  • numbness or tingling in the hands, feet, or lips
  • painful or difficult urination
  • pale skin
  • pounding in the ears
  • rapid breathing
  • sneezing
  • sore throat
  • sunken eyes
  • swelling of the hands, ankles, feet, or lower legs
  • tightness in the chest
  • troubled breathing with exertion
  • ulcers, sores, or white spots in the mouth
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • wrinkled skin
Less common
  • Abdominal or stomach pain
  • change in walking and balance
  • clumsiness or unsteadiness
  • decreased awareness or responsiveness
  • decreased frequency of urination
  • headache
  • muscle twitching or jerking
  • pounding in the ears
  • rhythmic movement of the muscles
  • seeing, hearing, or feeling things that are not there
  • seizures
  • severe constipation
  • severe sleepiness
  • shakiness in the legs, arms, hands, or feet
  • slow or fast heartbeat
  • thinking abnormalities
  • trembling or shaking of the hands or feet

If any of the following symptoms of overdose occur while taking fentanyl, get emergency help immediately:

Symptoms of overdose
  • Extremely shallow or slow breathing

Some fentanyl side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

More common
  • Back pain
  • diarrhea
  • difficulty having a bowel movement (stool)
  • difficulty with moving
  • discouragement
  • feeling sad or empty
  • irritability
  • lack or loss of strength
  • loss of interest or pleasure
  • muscle stiffness
  • pain in the joints
  • sleepiness or unusual drowsiness
  • tiredness
  • trouble concentrating
  • trouble sleeping
  • weight loss
Less common
  • Changes in vision
  • excessive muscle tone
  • feeling of constant movement of self or surroundings
  • feeling of warmth or heat
  • flushing or redness of the skin, especially on the face and neck
  • irritation, pain, or sores at the site of application
  • itching skin
  • muscle tension or tightness
  • rash
  • sensation of spinning
  • sweating
Incidence not known
  • Tooth pain
  • trouble with gums
  • trouble with teeth

After you stop taking this drug, it is possible that you may still experience side effects that need medical attention. If you notice any of the following side effects check with your doctor immediately:

  • Restlessness
  • speech disorder
  • stomach cramps
  • weakness

For Healthcare Professionals

Applies to fentanyl: buccal film, buccal tablet, compounding powder, injectable solution, nasal spray, oral lozenge, oral transmucosal lozenge, sublingual spray, sublingual tablet, transdermal device, transdermal film extended release

Nervous system

Very common (10% or more): Somnolence, dizziness
Common (1% to 10%): Sedation, pyrexia, fatigue, lethargy, tremor, headache, chills, irritability, malaise, confusion, abnormal thinking, anxiety, dysphoria
Uncommon (0.1% to 1%): Hyperesthesia
Very rare (less than 0.01%): Severe hemiplegic migraine
Frequency not reported: Slurred speech
Postmarketing reports: Loss of consciousness, vertigo, coma, shock, convulsion

Cases of seizures have occasionally been reported, but some investigators have suggested that the seizure-like events reported may have been episodes of fentanyl induced-rigidity.


Common (1% to 10%): Tachycardia
Uncommon (0.1% to 1%): Sinus tachycardia, chest pain, hypertension, hypotension, palpitations
Rare (less than 0.1%): Arrhythmias, cardiac arrest
Postmarketing reports: Circulatory depression

One report has suggested that epidural fentanyl may mask the pain of myocardial ischemia in patients treated with fentanyl for other reasons. Another report has suggested that QTc interval prolongation may occur in some patients receiving the related narcotic sufentanil. Another report has implicated fentanyl as a potential cause of pulsus alternans in a patient with aortic stenosis and congestive heart failure.

Nevertheless, fentanyl has been advocated by some as a satisfactory agent for coronary artery surgery.


Very common (10% or more): Nausea (18%), vomiting (10%), constipation
Common (1% to 10%): Dry mouth, abdominal distension, gastritis, dysphagia, dyspepsia, gastroesophageal reflux disease, ascites, hematemesis, taste perversion, abdominal pain, dehydration, anorexia, cachexia, vomiting, dry mouth, mouth ulcers/stomatitis, tongue edema
Uncommon (0.1% to 1%): Abdomen enlarged, flatulence
Rare (less than 0.1%): Choledochoduodenal sphincter spasm
Postmarketing reports: Ileus, dental caries, tooth loss, gingival recession, gingivitis, gingival bleeding, lip edema, pharyngeal edema, gum bleeding, ulcer


Uncommon (0.1% to 1%): Urinary retention
Very rare (less than 0.01%): Priapism


Common (1% to 10%): Application site irritation, pruritus
Uncommon (0.1% to 1%): Hyperhidrosis, rash
Rare (less than 0.1%): Systemic rashes


Rare (less than 0.1%): Anaphylaxis


Common (1% to 10%): Anemia, neutropenia, lymphadenopathy, thrombocytopenia, leukopenia, aspartate aminotransferase increased, blood alkaline phosphatase increased, blood glucose increased, blood lactate increased, hypoalbuminemia, vasodilation

The hemolysis observed may have been related to rapid injection of large volumes of hypotonic fentanyl solution. The authors therefore recommend slower injection rates and/or mixture in isotonic fluid.


Uncommon (0.1% to 1%): Oral candidiasis, cellulitis, pneumonia, urinary tract infection, oral herpes, gastroenteritis, laryngitis
Very rare (less than 0.01%): Recurrent herpes simplex infection following epidural administration


Common (1% to 10%): Asthenia, peripheral edema, weight decreased, hypokalemia, hyponatremia, hypocalcemia
Very rare (less than 0.01%): Syndrome of inappropriate antidiuretic hormone


Uncommon (0.1% to 1%): Hot flush


Common (1% to 10%): Fall/accidental injury, back pain, arthralgia, joint swelling, muscular weakness, myoclonus, involuntary muscle contractions, muscle rigidity (involving the respiratory musculature including the glottis)
Postmarketing reports: Abnormal gait/incoordination


Uncommon (0.1% to 1%): Vision blurred, dry eye
Rare (less than 0.1%): Abnormal vision


Common (1% to 10%): Depression, confusional state, hallucination, insomnia
Uncommon (0.1% to 1%): Anxiety, agitation, restlessness, agitation, disorientation, abnormal dreams, depersonalization, depression, emotional lability, euphoria, delirium


Common (1% to 10%): Dyspnea, rhinitis, yawning, dyspnea, respiratory distress, apnea, bradypnea, hypoventilation, respiratory depression
Uncommon (0.1% to 1%): Cough, increased bronchial secretion, dysphonia, pharyngolaryngeal pain, wheezing, hypoxia, exertional dyspnea
Very rare (less than 0.01%): Acute noncardiogenic pulmonary edema
Postmarketing reports: Respiratory arrest

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