Skip to Content

Trihexy Side Effects

Generic name: trihexyphenidyl

Medically reviewed by Last updated on Jan 17, 2021.

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

For the Consumer

Applies to trihexyphenidyl: oral elixir, oral tablet

Side effects requiring immediate medical attention

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:


  • Abdominal or stomach cramps or pain
  • bloating
  • constipation
  • delusions of persecution, mistrust, suspiciousness, or combativeness
  • excessive dryness of the mouth
  • false beliefs that cannot be changed by facts
  • loss of appetite
  • nausea or vomiting
  • seeing, hearing, or feeling things that are not there
  • skin rash
  • stomach pain
  • swollen, painful, or tender lymph glands on the side of the face or neck

Incidence not known

  • Anxiety
  • blurred vision
  • change in vision
  • decrease in frequency of urination
  • decrease in urine volume
  • difficult urination
  • difficulty in passing urine (dribbling)
  • disturbed behavior
  • dry mouth
  • enlarged pupils
  • eye pain
  • fast, pounding, or irregular heartbeat or pulse
  • hyperventilation
  • irritability
  • loss of vision
  • mental confusion
  • nervousness
  • painful urination
  • restlessness
  • shaking
  • shortness of breath
  • trouble sleeping

Side effects not requiring immediate medical attention

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

  • Drowsiness
  • weakness

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]


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]

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]


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


1. "Product Information. Artane (trihexyphenidyl)." Lederle Laboratories, Wayne, NJ.

2. Kalman T, Warner GM "Protracted vomiting following abrupt cessation of psychotropics: a case report." Can Psychiatr Assoc J 23 (1978): 163-5

3. Baker LA, Cheng LY, Amara IB "The withdrawal of benztropine mesylate in chronic schizophrenic patients." Br J Psychiatry 143 (1983): 584-90

4. McEvoy JP "A double-blind crossover comparison of antiparkinson drug therapy: amantadine versus anticholinergics in 90 normal volunteers, with an emphasis on differential effects on memory function." J Clin Psychiatry 48(9 suppl (1987): 20-3

5. Nomoto M, Thompson PD, Sheehy MP, Quinn NP, Marsden CD "Anticholinergic-induced chorea in the treatment of focal dystonia." Mov Disord 2 (1987): 53-6

6. Moreau A, Jones BD, Banno V "Chronic central anticholinergic toxicity in manic depressive illness mimicking dementia." Can J Psychiatry 31 (1986): 339-41

7. Burnett GB, Prange AJ Jr, Wilson IC, Jolliff LA, Creese IC, Synder SH "Adverse effects of anticholinergic antiparkinsonian drugs in tardive dyskinesia. An investigation of mechanism." Neuropsychobiology 6 (1980): 109-20

8. Hauser RA, Olanow CW "Orobuccal dyskinesia associated with trihexyphenidyl therapy in a patient with Parkinson's disease." Mov Disord 8 (1993): 512-4

9. Warne RW, Gubbay SS "Choreiform movements induced by anticholinergic therapy." Med J Aust 1 (1979): 465

10. McEvoy JP, McCue M, Spring B, Mohs RC, Lavori PW, Farr RM "Effects of amantadine and trihexyphenidyl on memory in elderly normal volunteers." Am J Psychiatry 144 (1987): 573-7

11. el-Yousef MK, Janowsky D, Davis JM, Sekerke HJ "Reversal of antiparkinsonian drug toxicity by physostigmine: a controlled study." Am J Psychiatry 130 (1973): 141-5

12. Glassman JN, Darko D, Gillin JC "Medication-induced somnambulism in a patient with schizoaffective disorder." J Clin Psychiatry 47 (1986): 523-4

13. Yassa R "Antiparkinsonian medication withdrawal in the treatment of tardive dyskinesia: a report of three cases." Can J Psychiatry 30 (1985): 440-2

14. West RR, Newgreen DB "Choreiform movements induced by anticholinergic therapy." Med J Aust 2 (1979): 87-8

15. Birket-Smith E "Abnormal involuntary movements induced by anticholinergic therapy." Acta Neurol Scand 50 (1974): 801-11

16. Kiloh LG, Smith JS, Williams SE "Antiparkinson drugs as causal agents in tardive dykinesia." Med J Aust 2 (1973): 591-3

17. McEvoy JP, Freter S "The dose-response relationship for memory impairment by anticholinergic drugs." Compr Psychiatry 30 (1989): 135-8

18. Koller WC "Disturbance of recent memory function in parkinsonian patients on anticholinergic therapy." Cortex 20 (1984): 307-11

19. Warnes H "Toxic psychosis due to antiparkinsonian drugs." Can Psychiatr Assoc J 12 (1967): 323-6

20. Laski E, Taleporos E "Anticholinergic psychosis in a bilingual: a case study." Am J Psychiatry 134 (1977): 1038-40

21. Wilcox JA "Psychoactive properties of benztropine and trihexyphenidyl." J Psychoactive Drugs 15 (1983): 319-21

22. Trend P, Trimble M, Wessely S "Schizophrenic psychosis associated with benzhexol (artane) therapy." J Neurol Neurosurg Psychiatry 52 (1989): 1115

23. Stephens DA "Psychotoxic effects of benzhexol hydrochloride (Artane)." Br J Psychiatry 113 (1967): 213-8

24. Friedman Z, Neumann E "Benzhexol-induced blindness in Parkinson's disease." Br Med J 1 (1972): 605

25. Blumensohn R, Razoni G, Shalev A, Munitz H "Bradycardia due to trihexyphenidyl hydrochloride." Drug Intell Clin Pharm 20 (1986): 786-7

26. Johnson AL, Hollister LE, Berger PA "The anticholinergic intoxication syndrome: diagnosis and treatment." J Clin Psychiatry 42 (1981): 313-7

27. Hussey HH "Physostigmine: value in treatment of central toxic effects of anti-cholinergic drugs." JAMA 231 (1975): 1066

28. Kulik AV, Wilbur R "Delirium and stereotypy from anticholinergic antiparkinson drugs." Prog Neuropsychopharmacol Biol Psychiatry 6 (1982): 75-82

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.