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Comtan Side Effects

Generic Name: entacapone

Note: This page contains information about the side effects of entacapone. Some of the dosage forms included on this document may not apply to the brand name Comtan.

In Summary

Common side effects of Comtan include: urine discoloration. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to entacapone: oral tablet

In addition to its needed effects, some unwanted effects may be caused by entacapone (the active ingredient contained in Comtan). In the event that any of these side effects do occur, they may require medical attention.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when taking entacapone:

More common:
  • Absence of or decrease in body movements
  • hyperactivity
  • increase in body movements
  • seeing, hearing, or feeling things that are not there
  • twisting
  • twitching
  • uncontrolled repetitive movements of the tongue, lips, face, arms, or legs
Less common:
  • Cough or hoarseness
  • fever or chills
  • lower back or side pain
  • painful or difficult urination
  • Confusion
  • muscle cramps
  • pain
  • shortness of breath
  • stiffness
  • unusual tiredness or weakness

Minor Side Effects

Some of the side effects that can occur with entacapone may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common:
  • Abdominal or stomach pain
  • constipation
  • diarrhea
  • dizziness
  • nausea
Less common:
  • Acid or sour stomach
  • anxiety
  • belching
  • bruising
  • burning feeling in the chest or stomach
  • difficult or labored breathing
  • dry mouth
  • heartburn
  • indigestion
  • irritability
  • loss of strength or energy
  • muscle pain or weakness
  • passing gas
  • restlessness
  • sleepiness or unusual drowsiness
  • small, red spots on the skin
  • stomach discomfort, upset, or tenderness
  • sweating increased
  • tightness in the chest
  • tremor
  • trouble sleeping
  • unusual or unpleasant (after) taste
  • unusual weak feeling

For Healthcare Professionals

Applies to entacapone: oral tablet

Nervous system

Very common (10% or more): Dyskinesia (up to 27%), hyperkinesia (10%)
Common (1% to 10%): Hypokinesia, dizziness, somnolence, taste perversion, aggravated parkinsonism, dystonia, headache, tremor
Frequency not reported: Falling asleep during activities of daily living
Postmarketing reports: Neuroleptic malignant syndrome[Ref]

There were no cases of neuroleptic malignant syndrome during clinical trials. Since market introduction, there have been isolated cases, especially following abrupt reduction or discontinuation of this drug and other concomitant dopaminergic drugs.[Ref]


Very common (10% or more): Nausea (up to 14%), diarrhea (up to 11%)
Common (1% to 10%): Abdominal pain, constipation, vomiting, dry mouth, dyspepsia, flatulence, gastritis, gastrointestinal disorders
Very rare (less than 0.01%): Anorexia
Postmarketing reports: Colitis[Ref]

In clinical trials, diarrhea occurred in approximately 10% of patients. It was generally mild to moderate, but in 1.3% of people it was severe. Upon discontinuation, diarrhea generally resolved. There have been postmarketing reports of drug-induced microscopic colitis, primarily lymphocytic colitis.[Ref]


Very common (10% or more): Urine discoloration (10%)[Ref]


The most commonly reported adverse reactions included dyskinesia, urine discoloration, diarrhea, nausea, hyperkinesia, abdominal pain, vomiting, and dry mouth.[Ref]


Common (1% to 10%): Dyspnea
Frequency not reported: Pulmonary fibrosis[Ref]


Common (1% to 10%): Increased sweating
Rare (less than 0.1%): Erythematous, maculopapular rash
Very rare (less than 0.01%): Urticaria
Frequency not reported: Skin hair, beard, and nail discolorations[Ref]


Common (1% to 10%): Back pain, falls, leg cramps
Postmarketing reports: Rhabdomyolysis[Ref]

Isolated cases of rhabdomyolysis have occurred in patients treated with this drug. The complicated nature of these cases makes it difficult to determine the role this drug may have had. Rhabdomyolysis has been reported secondary to severe dyskinesias or neuroleptic malignant syndrome (NMS) in patients with Parkinson's disease.[Ref]


Common (1% to 10%): Anxiety, insomnia, hallucinations, confusion, paranoia
Uncommon (0.1% to 1%): Agitation
Frequency not reported: Impulse control disorders including pathological gambling, increased libido, hypersexuality, compulsive spending or buying, binge eating and compulsive eating[Ref]


Common (1% to 10%): Purpura, decreased hemoglobin[Ref]

A clinically significant decrease in hemoglobin has been observed in 1.8% of patients. The underlying mechanism may involve decreased absorption of iron from the gastrointestinal tract.[Ref]


Common (1% to 10%): Fatigue, asthenia, pain, vertigo[Ref]


The incidence of myocardial infarction and other ischemic heart disease events was 0.43% and 1.54%, respectively, in an analysis of 13 double-blind studies involving 2082 patients.[Ref]

Common (1% to 10%): Ischemic heart disease events other than myocardial infarction (e.g., angina pectoris, postural hypotension
Uncommon (0.1% to 1%): Myocardial infarction[Ref]


Rare (less than 0.1%): Abnormal liver function tests
Postmarketing reports: Hepatitis with mainly cholestatic features[Ref]


1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

2. "Product Information. Comtan (entacapone)" Novartis Pharmaceuticals, East Hanover, NJ.

3. Cerner Multum, Inc. "Australian Product Information." O 0

Not all side effects for Comtan may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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