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Trihexy Side Effects

Generic name: trihexyphenidyl

Medically reviewed by Last updated on Dec 16, 2023.

Note: This document contains side effect information about trihexyphenidyl. Some dosage forms listed on this page may not apply to the brand name Trihexy.

Applies to trihexyphenidyl: oral elixir, oral tablet.

Serious side effects of Trihexy

Along with its needed effects, trihexyphenidyl (the active ingredient contained in Trihexy) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking trihexyphenidyl:


Incidence not known

Other side effects of Trihexy

Some side effects of trihexyphenidyl may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Incidence not known

For Healthcare Professionals

Applies to trihexyphenidyl: oral elixir, oral tablet.


The most commonly reported adverse reactions have included dry mouth, blurred vision, dizziness, nausea, and nervousness.[Ref]


Rare (less than 0.1%): Suppurative parotitis, dilation of colon, paralytic ileus

Frequency not reported: Dry mouth, difficulty swallowing, anorexia, constipation, nausea, vomiting[Ref]

Isolated cases of suppurative parotitis secondary to excessive dryness of the mouth have been reported.[Ref]

Nervous system

Frequency not reported: Drowsiness, headache, choreiform movements, neuroleptic malignant syndrome (with abrupt discontinuation), paraesthesia, numbness of fingers and dyskinesia, chorea, dizziness[Ref]


Rare (less than 0.1%): Delusions, hallucinations, paranoia

Frequency not reported: Nervousness, restlessness, euphoria, unusual excitement, impairment of memory or forgetfulness, confusion or delirium, psychiatric deterioration and psychotic flare-ups, toxic psychosis, depression, anxiety, agitation, insomnia[Ref]

Toxic psychosis, when present, tends to occur quickly, generally within several days to a week of initiating therapy or within hours after an acute overdose. However, occasionally the onset may be delayed by months. Symptoms generally resolve spontaneously within a few days after the discontinuation of medication.

Psychiatric deterioration and psychotic flare-ups have also been reported following withdrawal of therapy. Symptoms include delusions, hallucinations, aggression or violent behavior, and suicidal tendencies. In high dosages, it may produce euphorigenic effects. For this reason, it can be a drug of abuse.[Ref]


Frequency not reported: Blindness, blurred vision, mydriasis, cycloplegia, glaucoma, angle-closure glaucoma, pupil dilation, increased intraocular pressure, photophobia[Ref]


Frequency not reported: Tachycardia, paradoxical sinus bradycardia[Ref]


Frequency not reported: Urinary retention, urinary hesitancy, dysuria[Ref]


Frequency not reported: Heat stroke, hyperthermia, heat intolerance, weakness[Ref]


Frequency not reported: Allergic reaction, hypersensitivity


Rare (less than 0.1%): Skin rash

Frequency not reported: Anhidrosis, dry skin


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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.