A COMT inhibitor is a drug that inhibits the action of catechol-O-methyl transferase

Catechol-O-methyl transferase

Catechol-O-methyltransferase is one of several enzymes that degrade catecholamines such as dopamine, epinephrine, and norepinephrine. In humans, catechol-O-methyltransferase protein is encoded by the COMT gene...

. This enzyme is involved in degrading neurotransmitter

Neurotransmitter

Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

s. COMT inhibitors are used in the treatment of Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

.

Pharmaceutical examples include entacapone

Entacapone

Entacapone is a drug that functions as a catechol-O-methyl transferase inhibitor. It is used in the treatment of Parkinson's disease....

, tolcapone

Tolcapone

Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase . - Uses :Tolcapone is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication.- Chemistry :...

,
and nitecapone. Entacapone is only peripherally active, whereas both tolcapone

Tolcapone

Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase . - Uses :Tolcapone is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication.- Chemistry :...

 and nitecapone are active in both the periphery and central nervous system. Tolcapone

Tolcapone

Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase . - Uses :Tolcapone is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication.- Chemistry :...

and nitecapone are known to be hepatotoxic, whereas entacapone is not.

Reference s