Trihexyphenidyl

Key facts

• Trihexyphenidyl is an anticholinergic medicine that eases tremor, stiffness and muscle spasm in Parkinson's disease, and treats movement side effects caused by antipsychotic medicines.
• It's taken as tablets, usually several times a day; effects build up over the first few doses.
• Because it blocks acetylcholine throughout the body, it can trigger acute angle-closure glaucoma, cause urinary retention, and lead to confusion, particularly in older adults. Tell your prescriber about any eye or prostate problems before starting.
• Seek urgent care for sudden severe eye pain with blurred vision, inability to pass urine, or new confusion or hallucinations.

What trihexyphenidyl treats

Trihexyphenidyl treats the tremor and rigidity of Parkinson's disease and drug-induced extrapyramidal symptoms, the stiffness, tremor and restlessness that some antipsychotic medicines cause. It is not a treatment for restless legs syndrome.

How trihexyphenidyl works

Parkinson's disease and antipsychotic drugs disturb the balance between two brain chemicals, dopamine and acetylcholine. Trihexyphenidyl blocks acetylcholine at muscarinic receptors in the brain, restoring some of that balance and reducing the overactive nerve signals that cause muscle tightness and tremor.

Before you take it

• Avoid it if you have narrow-angle glaucoma, urinary retention, an enlarged prostate causing obstruction, or myasthenia gravis, unless your prescriber says otherwise.
• Tell your prescriber about any bowel obstruction or severe constipation.
• Combining it with other anticholinergic medicines, such as some antihistamines or antidepressants, adds to the risk of confusion, dry mouth and constipation.
• Use extra caution in older adults, who are more prone to confusion, memory problems and falls.

Side effects

Common effects include dry mouth, blurred vision, constipation, and dizziness on standing.

Stop and seek urgent medical care for any of these:

• Severe eye pain with blurred vision or halos around lights.
• Inability to urinate.
• Rapid heartbeat, severe flushing, or profuse sweating.
• Confusion, agitation, or hallucinations.

Safety essentials

• This medicine can trigger acute angle-closure glaucoma; treat sudden eye pain, vision change or halos around lights as an emergency.
• It reduces sweating, so avoid overheating or strenuous activity in hot weather, since this raises the risk of heatstroke.
• In older adults it increases the risk of confusion, memory problems and falls; long-term anticholinergic use is linked to cognitive decline, so ongoing need is reviewed regularly.
• Don't stop it suddenly after long-term use. Withdrawal can worsen movement symptoms, so your prescriber will reduce the dose gradually.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.