By Medically reviewed by hellodoktor

Generic Name: Trihexyphenidyl Brand Name(s): Generics only. No brands available. Avability: Rx Pregnancy Category: N


What is Trihexyphenidyl used for?

Trihexyphenidyl is used to treat symptoms of Parkinson’s disease or involuntary movements due to the side effects of certain psychiatric drugs (antipsychotics such as chlorpromazine/haloperidol). Trihexyphenidyl belongs to a class of medication called anticholinergics that work by blocking a certain natural substance (acetylcholine). This helps decrease muscle stiffness, sweating, and the production of saliva, and helps improve walking ability in people with Parkinson’s disease.

Anticholinergics can stop severe muscle spasms of the back, neck, and eyes that are sometimes caused by psychiatric drugs. It can also decrease other side effects such as muscle stiffness/rigidity (extrapyramidal signs-EPS). It is not helpful in treating movement problems caused by tardive dyskinesia and may worsen them.

How should I take 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.

Though it helps many people, this medication may sometimes cause addiction. This risk may be higher if you have a substance use disorder (such as overuse of or addiction to drugs/alcohol). Do not increase your dose, take it more often, or use it for a longer time than prescribed. Properly stop the medication when so directed. Some conditions may become worse when the drug is suddenly 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.

How do I store Trihexyphenidyl?

Trihexyphenidyl is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store Trihexyphenidyl in the bathroom or the freezer. There may be different brands of Trihexyphenidyl that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush Trihexyphenidyl down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Trihexyphenidyl?

Before taking trihexyphenidyl, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: personal or family history of glaucoma (angle-closure type), blockage of the bladder/esophagus/stomach/intestines (e.g., bowel obstruction), severe ulcerative colitis.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: 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), personal or family history of a substance use disorder (such as overuse of or addiction to drugs/alcohol).

This drug may make you dizzy or drowsy or blur your vision. Alcohol or marijuana can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. Avoid alcoholic beverages. Talk to your doctor if you are using marijuana.

To minimize dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.

This medication decreases saliva production, an effect that can increase gum and tooth problems (e.g., cavities, gum disease). Take special care with your dental hygiene (e.g., brushing, flossing) and have regular dental check-ups.

Liquid forms of this product may contain alcohol. Caution is advised if you have diabetes, alcohol dependence, or liver disease. Some medications (e.g., disulfiram, metronidazole) may cause a serious reaction when combined with alcohol. Tell your doctor if you are taking any medication that should not be used with alcohol. Ask your doctor or pharmacist about using this product safely.

This drug can cause decreased sweating, which could cause a severe rise in your body temperature (hyperthermia). The risk of this serious side effect is greater in hot weather, during vigorous exercise, and/or if you drink alcohol. Drink plenty of fluids and dress lightly while in hot weather and when exercising. If you experience signs of hyperthermia such as mental/mood changes, headache, or dizziness, promptly seek cool or air-conditioned shelter and/or stop exercising, and seek immediate medical attention. Consult your doctor for more details.

Older adults may be more sensitive to the side effects of this drug, especially dizziness, drowsiness, heatstroke, memory problems, difficulty urinating, and constipation. Dizziness and drowsiness can increase the risk of falling.

Children may be more sensitive to the effects of this drug, especially effects on heart rate.

This drug should be used only when clearly needed during pregnancy. Discuss the risks and benefits with your doctor.

It is not known if this drug passes into breast milk. Consult your doctor before breast-feeding.

Is it safe during pregnancy or breast-feeding?

There are no adequate studies in women for determining risk when using this Trihexyphenidyl during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking Trihexyphenidyl. Trihexyphenidyl is pregnancy risk category N according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk,
  • B=No risk in some studies,
  • C=There may be some risk,
  • D=Positive evidence of risk,
  • X=Contraindicated,
  • N=Unknown


Side effects

What side effects can occur from Trihexyphenidyl?

Drowsiness, dizziness, constipation, flushing, nausea, nervousness, blurred vision, or dry mouth may occur. These effects usually lessen as your body gets used to the medicine. If any of these effects persist or worsen, contact your doctor or pharmacist promptly.

To relieve dry mouth, suck on (sugarless) hard candy or ice chips, chew (sugarless) gum, drink water, or use a saliva substitute.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if any of these unlikely but serious side effects occur: decreased sexual ability, severe stomach/abdominal pain, difficult/painful swallowing, difficulty urinating, weakness.

Get medical help right away if you have any very serious side effects, including: 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, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.


What drugs may interact with Trihexyphenidyl?

This drug should not be used with the following medication because very serious interactions may occur: pramlintide.

If you are currently using the medication listed above, tell your doctor or pharmacist before starting trihexyphenidyl.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially: 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, safinamide, 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 are taking other products that cause drowsiness such as opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana, drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy or cough-and-cold products) because they may contain ingredients that cause drowsiness. Ask your pharmacist about using those products safely.

Trihexyphenidyl may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Does food or alcohol interact with Trihexyphenidyl?

Trihexyphenidyl may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with Trihexyphenidyl?

Trihexyphenidyl may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.


The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using this Trihexyphenidyl.

What is the dose of Trihexyphenidyl for an adult?

Usual Adult Dose for Extrapyramidal Reaction

4 to 10 mg orally each day. The total daily dose is best tolerated when administered in 2 or three equally separated doses.

Usual Adult Dose for Parkinson’s Disease

Initial: 1 mg/day; increase by 2 mg increments at intervals of 3 to 5 days

Usual dose: 6 to 10 mg/day in 3 to 4 divided doses; doses of 12 to 15 mg/day may be required

Drug-induced extrapyramidal symptoms: Initial: 1 mg/day; increase as necessary to usual range of 5 to 15 mg/day in 3 to 4 divided doses

Use in combination with levodopa: Usual range: 3 to 6 mg/day in divided doses

Renal Dose Adjustments

Due to a lack of pharmacokinetic data, there are no guidelines available for the dosing of trihexyphenidyl in patients with renal disease. If trihexyphenidyl is needed in this patient, therapy should be initiated with a low dosage and titrated conservatively. This patient may also be more sensitive to the anticholinergic effects of trihexyphenidyl and should be monitored closely.

Liver Dose Adjustments

Due to a lack of pharmacokinetic data, there are no guidelines available for the dosing of trihexyphenidyl in patients with liver disease. If trihexyphenidyl is needed in this patient, therapy should be initiated with a low dosage and titrated conservatively. This patient may also be more sensitive to the anticholinergic effects of trihexyphenidyl and should be monitored closely.


Trihexyphenidyl has cumulative effects. Therefore, continued supervision of the patient is recommended.

Trihexyphenidyl may impair mental and/or physical abilities. Patients should be cautioned about driving or operating dangerous machinery. The elderly may be particularly vulnerable to these effects.

Anticholinergic agents, including trihexyphenidyl, are not effective in controlling tardive dyskinesia (TD) and in some cases may aggravate it or induce previously suppressed symptoms. Trihexyphenidyl should be avoided in patients presenting with TD. If TD symptoms develop or worsen during treatment with trihexyphenidyl, prompt withdrawal of therapy will provide better chances of improving the condition.

Trihexyphenidyl occasionally intensifies mental symptoms in patients with preexisting psychiatric disorders.

Trihexyphenidyl should be used cautiously in patients with cardiac disorders, including a tachycardic tendency or hypertension, liver disorders, kidney disorders, prostatic hypertrophy, obstructive disease of the gastrointestinal or genitourinary tracts, or angle-closure glaucoma. Patients should have intraocular pressures checked at regular intervals.

Abrupt discontinuation of long-term trihexyphenidyl therapy may be associated with withdrawal and cholinergic rebound symptoms, including myalgias, diaphoresis, gastrointestinal distress, lethargy, depression, anxiety, tachycardia, orthostatic hypotension, hallucinations, and relapse or exacerbation of extrapyramidal effects. Withdrawal symptoms may be delayed by days to weeks after stopping medication.

Due to its hallucinogenic and euphorigenic effects, trihexyphenidyl is subject to potential misuse by drug abusers.

Since the use of trihexyphenidyl may, in some cases, continue indefinitely and since it has atropine-like properties, patients should be subjected to constant and careful long-term monitoring to avoid allergic and other untoward reactions.

Geriatric patients, particularly over the age of 60, commonly develop increased sensitivity to the actions of drugs of this type, and hence, require strict dosage regulation.

What is the dose of Trihexyphenidyl for a child?

Usual Pediatric Dose for Cerebral Spasticity


Children 2 to 17 years old:

Dystonia in cerebral palsy:

Initial: 0.1 to 0.2 mg/kg/day in three divided doses for 1 week; increase by 0.05 to 0.3 mg/kg/day in three divided doses for the second week; thereafter, titrate up weekly by 0.05 to 0.5 mg/kg/day in three divided doses as clinically tolerated

Maximum dose: 0.75 mg/kg/day

How is Trihexyphenidyl available?

Trihexyphenidyl is available in the following dosage forms and strengths:

  • Oral tablet,
  • Oral elixir.

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of Trihexyphenidyl, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Review Date: November 7, 2018 | Last Modified: September 12, 2019

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