Description: Trihexyphenidyl HCl, a tertiary amine antimuscarinic, inhibits the parasympathetic nervous system resulting in spasmolytic action on smooth muscle, weak mydriatic, antisialagogue and cardiovagal blocking effects.

Onset: W/in 1 hr.

Duration: 6-12 hr.


Absorption: Rapidly and well absorbed from the GI tract. Time to peak plasma concentration: 1.3 hr.

Metabolism: Undergoes hydroxylation of the alicyclic group.

Excretion: Via urine (as unchanged drug) and bile. Elimination half-life: 33 hr.

Trihexyphenidyl, an anticholinergic, is used to against the side effects of certain psychiatric drugs (antipsychotics such as chlorpromazine/haloperidol) that treats Parkinson’s disease or involuntary movements. It helps decrease muscle stiffness, sweating, and the production of saliva, and helps improve walking ability in people with Parkinson’s disease. It is not helpful in treating movement problems caused by tardive dyskinesia and may worsen them.

How to use trihexyphenidyl

Take this medication by mouth, usually 3 to 4 times a day with meals and at bedtime, or as directed by your doctor. Your doctor may start you at a low dose and increase your dose slowly to find the best dose for you. The dosage is based on your medical condition, age, and response to therapy.

If you are using the liquid form of this medication, measure your dose with a special measuring spoon or device. Do not use a household spoon because it may not provide the correct dose.

Take this medication regularly in order to get the most benefit from it. To help you remember, take it at the same times each day.

Take this medication at least 1 hour before antacids containing magnesium, aluminum, or calcium. Allow at least 1-2 hours between doses of trihexyphenidyl and certain drugs for diarrhea (adsorbent antidiarrheals such as kaolin, pectin, attapulgite). Take this medication at least 2 hours after ketoconazole. Antacids and some drugs for diarrhea may prevent the full absorption of trihexyphenidyl, and this product may prevent the complete absorption of ketoconazole when these products are taken together.

If you are taking this medication for side effects from another medication, your doctor may instruct you to take it on a regular schedule or only as needed. If you are taking this medication for Parkinson’s disease, your doctor may change the dose of your other medications (e.g., levodopa). Follow your doctor’s instructions closely.

Rarely, abnormal drug-seeking behavior (addiction) is possible with this medication. Do not increase your dose, take it more frequently, or take it for a longer time than prescribed. Properly stop the medication when so directed. Some conditions may become worse when the drug is abruptly stopped. Your dose may need to be gradually decreased.

When used for an extended period, this medication may not work as well and may require different dosing. Talk with your doctor if this medication stops working well. Inform your doctor if your condition persists or worsens.

Not available.

Contact your doctor or pharmacist promptly if any of these effects persist or worsen:

  • drowsiness
  • dizziness
  • constipation
  • flushing
  • nausea
  • nervousness
  • blurred vision
  • dry mouth

Tell your doctor immediately if any of these unlikely but serious side effects occur:

  • decreased sexual ability
  • severe stomach/abdominal pain
  • difficult/painful swallowing
  • difficulty urinating
  • weakness
  • chest pain
  • severe dizziness/fainting
  • high fever
  • fast/irregular/slow heartbeat
  • mental/mood changes (e.g., confusion, hallucinations, memory problems)
  • eye pain/swelling/redness
  • vision changes (such as seeing rainbows around lights at night)

A serious allergic reaction to this drug is unlikely.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.


  • Patients with medical history of:
    • alcohol use
    • breathing problems (e.g., asthma, emphysema)
    • diarrhea caused by an infection
    • heart problems (e.g., angina, heart attack, heart failure, fast/irregular heartbeat)
    • high/low blood pressure
    • intestinal problems (e.g., chronic constipation, ileus, ulcerative colitis)
    • kidney disease
    • liver disease
    • mental/mood problems (e.g., anxiety, dementia, psychosis)
    • certain muscle disease (myasthenia gravis)
    • certain nerve disease (autonomic neuropathy)
    • seizure
    • stomach problems (e.g., acid reflux, hiatal hernia, ulcer)
    • stroke
    • overactive thyroid (hyperthyroidism)
    • problems urinating (e.g., due to enlarged prostate, neurogenic bladder)
  • Patients with personal or family history of glaucoma (angle-closure type), blockage of the bladder/esophagus/stomach/intestines (e.g., bowel obstruction), or severe ulcerative colitis.
  • Allergic reaction to this medication.
  • May make you dizzy or drowsy or cause blurred vision.
  • Increase gum and tooth problems (e.g., cavities, gum disease).
  • Caution is advised if you have diabetes, alcohol dependence, or liver disease because liquid forms of this product may contain alcohol.
  • This drug can cause decreased sweating, which could cause a severe rise in your body temperature (hyperthermia).
  • Older adults may be more sensitive to the side effects of this drug, especially:
    • dizziness
    • drowsiness
    • heatstroke
    • memory problems
    • difficulty urinating
    • constipation
  • Children may be more sensitive to the effects on heart rate.
  • Used only when clearly needed during pregnancy.
  • Consult your doctor before breast-feeding.

Consult your doctor regarding the precautions mentioned above.


This drug should not be used with Pramlintide because very serious interactions may occur.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially:

  • amantadine
  • anticholinergics/antispasmodics (e.g., belladonna alkaloids, clidinium)
  • certain antiarrhythmics (e.g., disopyramide, quinidine)
  • corticosteroids (e.g., prednisone)
  • MAO inhibitors (isocarboxazid, linezolid, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, selegiline, tranylcypromine)
  • motion sickness medication (e.g., meclizine, scopolamine)
  • potassium tablets/capsules, tricyclic antidepressants (e.g., amitriptyline, doxepin)

Tell your doctor or pharmacist if you also take drugs that cause drowsiness such as:

  • certain antihistamines (e.g., diphenhydramine)
  • anti-seizure drugs (e.g., carbamazepine)
  • medicine for sleep or anxiety (e.g., alprazolam, diazepam, zolpidem)
  • muscle relaxants
  • narcotic pain relievers (e.g., codeine)
  • psychiatric medicines (e.g., risperidone, trazodone)

Check the labels on all your medicines (e.g., cough-and-cold products) because they may contain anticholinergics or drowsiness-causing ingredients. Ask your pharmacist about the safe use of those products.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.


If overdose is suspected, contact a poison control center or emergency room immediately. Symptoms of overdose may include: unusually fast/slow heartbeat, slow/shallow breathing, unconsciousness, seizures, loss of coordination, fever, hot/dry/flushed skin, widened pupils, change in vision, change in the amount of urine, confusion, hallucinations.


Do not share this medication with others.

Laboratory and/or medical tests (e.g., eye exams) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

People with Parkinson’s disease may have an increased risk for developing skin cancer (melanoma). If you are taking this drug to treat Parkinson’s disease, tell your doctor promptly if you notice a change in the appearance or size of moles or other unusual skin changes. Ask your doctor if you should have regular skin exams.

Missed Dose

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.


Store at room temperature between 68-77 degrees F (20-25 degrees C) away from light and moisture. Do not store in the bathroom. Keep all medicines away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.


Also marketed as

  • Artane [ Wyeth ]

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