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Dr. Vijayakumar D.R MBBS, DPM, DNB (NIMHANS), CCST (UK)
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Patient Infor Mation On Antiparkinsonian Drugs


The name of your medication is: trihexyphenydyl


This medication is used to treat muscle side effects that some individuals experience when they are being treated with antipsychotics (narcoleptic) drugs. These muscle side effects can include:

  • Muscle spasms or contractions (e. g., in the neck , eyes or tongue)
  • Muscle stiffness, tremor, or a shuffling walk
  • Feeling restless, unable to sit still, having a need to pace
  • Muscle weakness or a slowing of movement

How quickly will the drug start working? 

Antiparkinsonian drugs can reduce or stop the above side effects, usually within an hour. Sometimes they have to be given by injection for a quicker effect.

How long should you take this medication?

Most patients take antiparkinsonian drugs for-2-3 weeks, usually when first prescribed an antipsychotic drug, and while its dose is being stabilized. The doctor will then reduce the dose of this drug to see if the muscle symptoms return; if not, you may be advised to stop using this medication. Do not increase the dose or stop the drug without consulting with your doctor.

Some patients need to use an antiparkinsonian drug for longer time periods, because they are more sensitive to muscle side effects from the antipsychotic drug they are receiving . Others require it only from time to time, I. e., PRN or as need basis (e. g., for 1 week after receiving an injection of an antipsychotic). 

Side Effects

Side effects occur, to some degree, with all medication. They are usually not serious and do not occur in all individuals. Most will decrease or disappear with time. If a side effect continues, speak to your doctor about appropriate treatment. 

Common side effects that can occur with antiparkinsonian drugs include:

  • Dry mouth- Sour candy and sugarless gum help increase saliva in your mouth; try to avoid sweet, calorie-laden beverages. Drink water and brush your teeth
  • Blurred vision-This usually occurs at the start of treatment and may last 1-2 weeks. Reading under a bright light or at a distance may help; a magnifying glass can be of temporary use. If the problem continues, consult your doctor.
  • Constipation-Increase bulk foods in your diet (e. g., salads, bran) and drink plenty of fluids. Some individuals find a bulk laxative or a stool softener helps regulate their bowels. If these remedies are not effective, consult your doctor or pharmacist.
  • Drowsiness and lethargy-This problem goes away with time. Use of other drugs that make you drowsy will worsen the problem. Avoid driving a car or operating machinery if drowsiness persists.
  • Nausea or heartburn -If this happens, take the medication with food

Less common side effects that you should report to your physician IMMEDIATELY include: 

  • Disorientation, confusion, worsening of your memory, increase in psychotic symptoms
  • Inability to have a bowel movement (more than 2-3 days)
  • Inability to pass urine (more than 24 hours)
  • Skin rash

Let your doctor know as soon as possible if you miss your period or suspect you may be pregnant


  1. Do not increase your dose without consulting your doctor
  2. Check with your doctor or pharmacist before taking other drugs, including over-the-counter medication such as cold remedies
  3. This drug may impair the mental and physical abilities required for driving a car or operating machinery. Avoid these activities if you feel drowsy or slowed down.
  4. This drug may increase the effects of alcohol, making you more sleepy, dizzy and lightheaded
  5. Avoid exposure to extreme heat and humidity (e. g., saunas) since this drug may affect your body’s ability to regulate temperature changes.
  6. Store your medication in a clean, dry area at room temperature. Keep all medication out of the reach of children.

If you have any questions regarding this medication, do not hesitate to contact your doctor, pharmacist, or nurse