COMT inhibitors (entacapone, opicapone)

COMT inhibitors is the name used to describe a class of Parkinson’s drugs.

You will be prescribed an unbranded COMT inhibitor medication such as entacapone, or a branded COMT inhibitor such as Comtess.

Due to ongoing issues with fuel supply in the UK, there have been concerns about potential delays in the delivery of drug supplies to pharmacies across all 4 nations. However, the Royal Pharmaceutical Society has made assurances that deliveries of essential medication are continuing as usual to pharmacies. If you're taking medication for your Parkinson's, we recommend waiting until you have used up your existing supply before getting a new one.

If you are having any difficulty with renewing your medication, please get in touch with our helpline, who will be able to advise you further, on 0808 800 0303.

Types of COMT inhibitor drugs

Below are the types of COMT inhibitor drugs. The generic names are written in bold and the brand names are written underneath in bullet points.


  • Comtess (tablets)

Co-careldopa and entacapone

  • Stalevo (tablets)
  • Sastravi (tablets)
  • Stanek (tablets)


  • Tasmar (tablets)


  • Ongentys (tablets)

COMT inhibitor drugs: an introduction

Levodopa can boost the supply of dopamine in your brain. COMT inhibitors can block an enzyme that breaks down levodopa medication. This helps it to work more effectively.

COMT inhibitors do not help to manage the symptoms of Parkinson’s on their own – they have to be used with levodopa.

Your specialist might prescribe them if your dose of levodopa is not working for long enough.

It will also help your levodopa medication to work more smoothly in controlling your symptoms.

Helping levodopa work more smoothly

COMT inhibitors can help when levodopa is not working for long enough and starts to wear off between doses.They can help to reduce your ‘off’ time, when you have more trouble with your Parkinson’s symptoms, and increase the amount of ‘on’ time, when your symptoms are more controlled.

Taking less levodopa

In many cases, you will be able to take a lower dose of levodopa and less often. 

Coloured urine and diarrhoea

COMT inhibitors will colour your urine a bright reddish orange colour but this isn’t harmful.

You may experience diarrhoea weeks or months after starting co-careldopa and entacapone (Stalevo, Sastravi, Stanek). If this happens contact your specialist or Parkinson’s nurse for advice.

Liver damage

With tolcapone (Tasmar), there is a risk of liver damage that can be fatal and you will need regular blood tests to check the health of your liver. It is rare, but for this reason, it is only used if you can’t take entacapone, where no risk of liver damage has been seen. Because of this we have not included further information about tolcapone here.

Worse levodopa side effects

Involuntary movements (dyskinesia) and sickness may get worse because COMT inhibitors strengthen the effects of levodopa. If this happens, your specialist or Parkinson’s nurse can reduce your dose of levodopa.

Impulsive and compulsive behaviours

Behaviours may involve gambling, becoming a ‘shopaholic’, binge eating or focusing on sexual feelings and thoughts. This can have a huge impact on people’s lives including family and friends.

Not everyone who takes Parkinson’s medication will experience impulsive and compulsive behaviours, so these side effects should not put you off taking your medication to control your symptoms.

Find out more about impulsive and compulsive behaviours.

Other side effects

The patient information leaflet that comes with your medication will tell you the full range of side effects that you may experience.

Some of these include:

  • sleeping problems
  • loss of appetite
  • dizziness
  • fainting
  • falls
  • hallucinations
  • headaches
  • confusion
  • dry mouth
  • chest pain
  • sleepiness

If you are allergic to peanuts or soya, make sure you tell your specialist and Parkinson’s nurse as you may not be able to take some COMT inhibitors.

Find out more about the side effects of Parkinson's drugs

Taking COMT inhibitor drugs: Entacapone, co-careldopa and entacapone, opicapone

Entacapone is a COMT inhibitor drug used to manage the symptoms of Parkinson’s. The brand name of entacapone is Comtess.

If you’ve had Parkinson’s for some time and your symptoms get worse between each dose of medication, you may be prescribed entacapone (Comtess). It works to increase the effectiveness of the levodopa medication you are taking and stop it from being broken down in the body. 

Taking entacapone (Comtess)

The most recent information on your specific medication will be on your patient information leaflet that comes with your packet. Always read it carefully before you start your treatment.

For detailed advice you should speak to your healthcare professional about how to take entacapone so that it works well for your Parkinson’s. Below we have included an overview of how to take entacapone (Comtess) medication.

You should take entacapone (Comtess) tablets at the same time as your co-beneldopa, or co-careldopa, levodopa medication.

Entacapone increases the effectiveness of your co-beneldopa, or co-careldopa, levodopa medication. But too much levodopa can create side effects. So when you start taking entacapone, your specialist or Parkinson’s nurse may need to adjust the amount of levodopa drugs that you take.

You can take your entacapone medication before you eat a meal.

When you take your entacapone (Comtess) tablets it may help to avoid any medicines or vitamin supplements with iron in them. Iron can mean that less entacapone gets into the parts of the body where it is needed. Talk to your specialist or Parkinson’s nurse for more information about this. 

Stalevo and Sastravi are branded versions of co-careldopa and entacapone medication. This means they combine the levodopa medication co-careldopa with entacapone.

The entacapone helps to make the levodopa component stronger which can help you control your symptoms.

Using this combination drug also means that it is convenient for people to take.

Taking co-careldopa and entacapone (Stalevo, Sastravi)

You may be prescribed co-careldopa and entacapone (Stalevo and Sastravi) if levodopa medication alone is not able to control motor fluctuations you experience at the end of your dose.

The maximum dose of Stalevo and Sastravi medication is usually between 7–10 tablets, depending on the strength you are prescribed.

Your healthcare professional will be best placed to advise you on when to take your medication and exactly how much to take.

Opicapone (Ongentys) is a type of COMT inhibitor medication. If you take levodopa for a long time, you may experience end of dose motor fluctuations when your symptoms are poorly controlled before your next dose is due. If this happens you can take opicapone with your levodopa medication to ease this issue.

Opicapone strengthens your levodopa medication to make it work better than when it is taken alone.

Taking opicapone (Ongentys)

The most recent and complete information on your specific drug will be on your patient information leaflet that comes with your medication packet. Always read it carefully before you start your treatment.

For detailed information you should follow the advice of your doctor about how to take opicapone (Ongentys) so that it works well for your Parkinson’s.

You should take opicapone once a day at bedtime. You should do this at least one hour before or after your levodopa medication.

Because opicapone is taken with levodopa to make it work well and reduce side effects, your healthcare professional may need to adjust the amount of levodopa you take. You should discuss this with them.

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Last updated August 2019. We review all our information within 3 years. If you'd like to find out more about how we put our information together, including references and the sources of evidence we use, please contact us at [email protected]