Thorazine (chlorpromazine) is an injection medication that may be prescribed off-label to help manage movement disorders such as chorea in people with Huntington’s disease.

How Thorazine works

Thorazine is a type of antipsychotic therapy, called a phenothiazine. It was developed in the 1950s to treat mental disorders such as schizophrenia.

Mental disorders can be caused by the overactivation of the dopamine system in the brain. Dopamine is a type of chemical messenger, called a neurotransmitter, which carries signals between nerve cells. When dopamine is released by a nerve cell, it binds to and activates a receptor found on the adjacent nerve cell to transmit the signal.

Dopamine acts in several areas of the brain and has multiple roles, including the regulation of mood and the control of movement. Chorea, the involuntary movements associated with Huntington’s disease, can be caused by an inappropriate activation of dopaminergic neurons.

Thorazine is an antagonist of several neurotransmitter receptors, including dopamine. By binding to the receptor in the place of dopamine, it prevents dopamine from accessing the receptor to block the transmission of the signal. Ultimately, this should reduce overactivation of nerves controlling movement, and ease the symptoms of chorea.

Additional information

Thorazine may significantly reduce the action of dopamine, causing such Parkinson’s disease-like symptoms as muscle rigidity, tremors, and slowed movement. Additional effects may include dystonia (muscle spasms or contractions), akathisia (restless legs syndrome), and dyskinesia (involuntary movements).

Commonly reported side effects of Thorazine can include drowsiness, dizziness, skin reactions (such as rashes), dry mouth, orthostatic hypotension (low blood pressure when getting up from a sitting or lying position), amenorrhea (missed menstrual periods), galactorrhea (milky discharge from the nipples), and weight gain.

Thorazine is classed as a first-generation antipsychotic and has been used to treat schizophrenia and other conditions since the 1950s. No clinical trials have specifically assessed its effectiveness in Huntington’s patients.

Thorazine may be prescribed off-label for Huntington’s disease. This means that while it may have beneficial effects, it is not specifically approved for Huntington’s by regulatory bodies, such as the U.S. Food and Drug Administration (FDA).

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