COMT Inhibitors for Parkinson's Disease

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COMT Inhibitors for Parkinson's Disease


Generic NameBrand Name

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.
  • Sudden and uncontrollable movements (dyskinesias). COMT inhibitors will allow the dose of levodopa to be decreased, which can reduce the severity of dyskinesias.

How Well It Works

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

  • Both increase "on" time and decrease "off" time by 1 to 2 hours a day.
  • Reduce motor fluctuations caused by the wearing-off effect of levodopa.
  • Improve motor function and the ability to do daily activities without increasing the dosage of levodopa in people taking levodopa who have not developed dose-related motor fluctuations. The levodopa dosage usually can be decreased without giving up any control over symptoms, because the COMT inhibitor makes a larger portion of the levodopa dosage available to the brain.

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:

  • Trouble breathing.
  • Hives.
  • Swelling of your face, lips, tongue, or throat.


Call your doctor if you have:

  • 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:

  • Belly pain or nausea.
  • Constipation or diarrhea.
  • Dizziness.
  • Fatigue.

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

What To Think About

Entacapone can cause a change in the colour of your urine. It can turn your urine brownish orange.

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. Poewe W (2004). The role of COMT inhibition in the treatment of Parkinson's disease. Neurology, 62(1, Suppl 1): S31–S38.


By Healthwise Staff
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Primary Medical Reviewer Andrew Swan, MD, CCFP, FCFP - Family Medicine
Specialist Medical Reviewer G. Frederick Wooten, MD - Neurology
Last Revised February 1, 2011

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.