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COMT Inhibitors for Parkinson's Disease


Generic Name Brand Name
entacapone Comtan
tolcapone Tasmar

How It Works

Catechol O-methyltransferase (COMT) inhibitors allow a larger amount of levodopa to reach the brain, which raises dopamine levels there. They help provide a more stable, constant supply of levodopa, which makes its beneficial effects last longer.

COMT inhibitors are always taken in combination with levodopa. They do not have any effect on Parkinson's disease symptoms by themselves.

Why It Is Used

COMT inhibitors are used in combination with levodopa to treat people with Parkinson's disease who have:

  • Times between doses of levodopa where the medicine stops working (called wearing-off).
  • Unpredictable "off" periods. This does not have to happen between doses of levodopa but can happen anytime.
  • A stable response to levodopa (no "off" periods or wearing-off effect) but want greater relief from their symptoms without increasing their levodopa dosage.

How Well It Works

COMT inhibitors are helpful to many people who have Parkinson's disease. Treatment with tolcapone or entacapone can:1

  • Decrease "off" time.
  • Reduce the amount of levodopa you need to take.
  • Improve motor function and the ability to do daily activities as measured by a standard Parkinson's disease test.

A combination medicine (Stalevo) combines entacapone, levodopa, and carbidopa. This may be more convenient for some people, because they would need to take only one pill instead of two.

Side Effects

All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

  • Usually the benefits of the medicine are more important than any minor side effects.
  • Side effects may go away after you take the medicine for a while.
  • If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.

Call 911 or other emergency services right away if you have:


Call your doctor if you have:

  • Hives.
  • An increase or decrease in controlled body movements.
  • Hyperactivity.
  • Hallucinations.
  • Uncontrollable movements of the tongue, lips, face, arms, or legs.

Common side effects of this medicine include:


Call your doctor right away if you have:

  • Signs of liver damage, such as:
    • Dark urine.
    • Itching.
    • Light-colored stools.
    • Loss of appetite.
    • Continuing nausea.
    • Pain or tenderness in the upper right part of your belly.
    • Unusual drowsiness, tiredness, weakness, or feeling sluggish.
    • Yellow eyes or skin.

Call your doctor if you have:

Common side effects of this medicine include:

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Both of these drugs can cause a change in the color of your urine. Entacapone can turn your urine brownish orange. Tolcapone can turn your urine bright yellow. You do not need to worry about this. But if you are taking tolcapone and your urine turns dark brown along with the other signs of liver damage listed above, call your doctor immediately.

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.


  1. Stowe R, et al. (2010). Evaluation of the efficacy and safety of adjuvant treatment to levodopa therapy in Parkinson's disease patients with motor complications. Cochrane Database of Systematic Reviews (7).

By Healthwise Staff
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Specialist Medical Reviewer G. Frederick Wooten, MD - Neurology
Current as of March 12, 2014

WebMD Medical Reference from Healthwise

Last Updated: March 12, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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