Medical Editor: John P. Cunha, DO, FACOEP Last updated on RxList: 10/4/2021
Comtan Side Effects Center

What Is Comtan?

Comtan (entacapone) is a COMT inhibitor used together with carbidopa and levodopa to treat "wearing-off" symptoms of Parkinson's disease, such as stiffness, tremors, muscle spasms, and poor muscle control. Common side effects of Comtan include:

  • nausea,
  • vomiting,
  • diarrhea,
  • constipation,
  • unwanted/uncontrolled movements,
  • increased sweating,
  • drowsiness,
  • dizziness,
  • lightheadedness upon standing,
  • tiredness,
  • dry mouth,
  • gas,
  • abdominal or stomach pain,
  • back pain,
  • brownish-orange colored urine (this side effect is harmless), and
  • falling asleep.

Tell your doctor if you have serious side effects of Comtan including:

  • mental/mood changes (such as confusion, hallucinations),
  • unusual strong urges (such as increased gambling, increased sexual urges),
  • fever,
  • muscle stiffness,
  • persistent diarrhea,
  • easy bleeding or bruising,
  • sore or painful muscles,
  • muscle weakness,
  • trouble breathing, or
  • pain with breathing.

The recommended dose of Comtan is one 200 mg tablet taken together with each levodopa/carbidopa dose to a maximum of 8 times daily (200 mg x 8 = 1600 mg per day). Comtan may interact with apomorphine, bitolterol, cholestyramine, dobutamine, epinephrine, isoetharine, isoproterenol, methyldopa, probenecid, or antibiotics. Tell your doctor all medications you are taking. During pregnancy, Comtan should be used only when prescribed. It is not known whether this drug passes into breast milk. Consult your doctor before breastfeeding.

Our Comtan (entacapone) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Parkinson's disease is only seen in people of advanced age. See Answer
Comtan Consumer Information

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Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • agitation, confusion, unusual thoughts or behavior;
  • hallucinations (hearing or seeing something that is not there);
  • very stiff (rigid) muscles, high fever, sweating, fast or uneven heartbeats, tremors, feeling like you might pass out;
  • severe or ongoing diarrhea;
  • restless muscle movements in your eyes, tongue, jaw, or neck (or worsening of Parkinson symptoms); or
  • unexplained muscle pain, tenderness, or weakness especially if you also have fever, unusual tiredness, and dark colored urine.

You may notice that your urine appears orange, red, brown, or black in color. This is not a harmful side effect unless you also have muscle pain and unusual weakness.

Common side effects may include:

  • dizziness, drowsiness;
  • nausea, vomiting, stomach pain;
  • diarrhea;
  • dry mouth; or
  • uncontrolled muscle movements.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Comtan (Entacapone)


Dementia, Alzheimer's Disease, and Aging Brains See Slideshow
Comtan Professional Information


Because clinical studies are conducted under widely varying conditions, the incidence of adverse reactions (number of unique patients experiencing an adverse reaction associated with treatment per total number of patients treated) observed in the clinical studies of a drug cannot be directly compared to the incidence of adverse reactions in the clinical studies of another drug and may not reflect the incidence of adverse reactions observed in practice.

A total of 1,450 patients with Parkinson’s disease were treated with Comtan in premarketing clinical studies. Included were patients with fluctuating symptoms, as well as those with stable responses to levodopa therapy. All patients received concomitant treatment with levodopa preparations, however, and were similar in other clinical aspects.

The most commonly observed adverse reactions (incidence at least 3% greater than placebo) in double-blind, placebo-controlled studies (N=1,003) associated with the use of Comtan were: dyskinesia, urine discoloration, diarrhea, nausea, hyperkinesia, abdominal pain, vomiting, and dry mouth. Approximately 14% of the 603 patients given entacapone in the double-blind, placebo-controlled studies discontinued treatment due to adverse reactions, compared to 9% of the 400 patients who received placebo. The most frequent causes of discontinuation in decreasing order were: psychiatric disorders (2% vs. 1%), diarrhea (2% vs. 0%), dyskinesia and hyperkinesia (2% vs. 1%), nausea (2% vs. 1%), and abdominal pain (1% vs. 0%).

Adverse Event Incidence In Controlled Clinical Studies

Table 4 lists treatment-emergent adverse events that occurred in at least 1% of patients treated with entacapone participating in the double-blind, placebo-controlled studies and that were numerically more common in the Comtan group, compared to placebo. In these studies, either Comtan or placebo was added to levodopa and carbidopa (or levodopa and benserazide).

Table 4: Summary of Patients with Adverse Events after Start of Trial Drug Administration At least 1% in Comtan Group and Greater Than Placebo

SYSTEM ORGAN CLASS   Preferred term Comtan Placebo
(n = 603) (n = 400))
% of patients % of patients
  Sweating increased 2 1
  Back pain 2 1
  Dyskinesia 25 15
  Hyperkinesia 10 5
  Hypokinesia 9 8
  Dizziness 8 6
  Taste perversion 1 0
  Anxiety 2 1
  Somnolence 2 0
  Agitation 1 0
  Nausea 14 8
  Diarrhea 10 4
  Abdominal pain 8 4
  Constipation 6 4
  Vomiting 4 1
  Mouth dry 3 0
  Dyspepsia 2 1
  Flatulence 2 0
  Gastritis 1 0
  Gastrointestinal disorders 1 0
  Dyspnea 3 1
  Purpura 2 1
  Urine discoloration 10 0
  Back pain 4 2
  Fatigue 6 4
  Asthenia 2 1
  Infection bacterial 1 0

Effects Of Gender And Age On Adverse Reactions

No differences were noted in the rate of adverse events attributable to entacapone by age or gender.

Postmarketing Reports

The following spontaneous reports of adverse events temporally associated with Comtan have been identified since market introduction and are not listed in Table 4. Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish causal relationship to Comtan exposure.

Hepatitis with mainly cholestatic features has been reported.

Read the entire FDA prescribing information for Comtan (Entacapone)

© Comtan Patient Information is supplied by Cerner Multum, Inc. and Comtan Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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