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Comtan Side Effects

Generic name: entacapone

Medically reviewed by Last updated on May 24, 2021.

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


Common side effects of Comtan include: urine discoloration. Continue reading for a comprehensive list of adverse effects.

Applies to entacapone: oral tablets.

Side effects include:

Dyskinesia, nausea, hyperkinesia, diarrhea, urine discoloration, hypokinesia, dizziness, abdominal pain, constipation, fatigue.

For Healthcare Professionals

Applies to entacapone: oral tablet.

Nervous system

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): 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]


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]


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%): Back pain, falls, leg cramps

Postmarketing reports: Rhabdomyolysis[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]

Frequently asked questions


1. "Product Information. Comtan (entacapone)." Novartis Pharmaceuticals (2001):

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

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

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.