COMT Inhibitors

COMT Inhibitors – Deliver more levadopa to the brain

COMT (Catechol-O -methyl transferase) inhibitors such as entacapone and tolcapone may be used to increase the peripheral half-life of levodopa, thereby delivering more levodopa to the brain over a longer time. COMT inhibitors do not help Parkinson’s on their own – they have to be used with the drug levodopa.

COMT inhibitors reduce Parkinson’s symptoms by blocking an enzyme that breaks down levodopa, prolonging its effect. When used with levodopa, COMT inhibitors can reduce the daily ‘off’ time and increase the ‘on’ time. In many cases, the dose and frequency that levodopa is taken can also be reduced.

Parkinson's COMT and Levodopa

Generic drug names and brand names

  • Entacapone (Comtess)

Side effects

The NHS website for Comtess, a standard COMT drug, states the following potential side effects:

Very common

  • Nausea
  • Problems controlling movement
  • Reddish-brown discolouration of urine


  • Abnormal muscle movement
  • Confusion
  • Constipation
  • Diarrhoea – seek medical advice if you have diarrhoea
  • Difficulty sleeping
  • Dry mouth
  • Falls
  • Feeling dizzy
  • Hallucinations
  • Heart problems such as Angina
  • Hyperactivity
  • Stomach pain
  • Strange dreams
  • Sweating
  • Tiredness
  • Vomiting
  • Worsening of Parkinson’s symptoms

For more information

Go to the Parkinson’s UK page on COMT Inhibitors – click here