Trihexane Side Effects

Generic Name: trihexyphenidyl

Note: This page contains side effects data for the generic drug trihexyphenidyl. It is possible that some of the dosage forms included below may not apply to the brand name Trihexane.

It is possible that some side effects of Trihexane may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to trihexyphenidyl: oral capsule extended release, oral elixir, oral tablet

As well as its needed effects, trihexyphenidyl (the active ingredient contained in Trihexane) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking trihexyphenidyl, check with your doctor immediately:

  • 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

Some trihexyphenidyl side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

More common
  • Dizziness
  • mild nausea
  • nervousness
Incidence not known
  • Drowsiness
  • weakness

For Healthcare Professionals

Applies to trihexyphenidyl: oral elixir, oral tablet


Most adverse effects of trihexyphenidyl (the active ingredient contained in Trihexane) are extensions of its pharmacologic activity and are anticholinergic in nature. Between 30% and 50% of all patients experience minor side effects (dry mouth, nausea, blurred vision, dizziness, nervousness). Elderly patients and those with underlying organic brain disease tend to be the most susceptible, especially to the central effects.


Gastrointestinal side effects have included dry mouth, difficulty swallowing, anorexia, constipation, nausea, and vomiting. A reduction in dosage will sometimes help alleviate these problems. Paralytic ileus may develop, particularly in patients on concomitant phenothiazine or tricyclic antidepressant therapy, and may occasionally be fatal. Upon withdrawal of medication, nausea and vomiting may occur due to a cholinergic rebound.

Nervous system

Bucco-linguo-masticatory dyskinesias and chorea have been reported mostly in elderly patients being treated for Parkinson's disease with various anticholinergic agents, including trihexyphenidyl (the active ingredient contained in Trihexane)

Nervous system side effects have included depression, anxiety, listlessness, drowsiness, numbness of fingers and dyskinesia. Chorea has been reported at higher dosages (>=15 mg/day). Trihexyphenidyl may also aggravate symptoms of tardive dyskinesia or elicit previously suppressed symptoms. Sleepwalking has been attributed to drugs or combination of drugs with anticholinergic activity.

Cognitive deficits, such as impairment of recent and short-term memory and inability to concentrate, may occur with clinical doses of anticholinergic agents and may be dose-related.


Psychiatric side effects have included toxic psychosis which manifested as confusion, disorientation, agitation, excitation, memory impairment, delusions and hallucinations (usually visual, but may be auditory or tactile or all three), at toxic and therapeutic dosages (2% to 4%, up to 19% in elderly patients). 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, trihexyphenidyl (the active ingredient contained in Trihexane) may sometimes produce euphorigenic effects. For this reason, it can be a drug of abuse.

Toxic psychosis, when present, tends to occur quickly, generally within several days to a week of initiating trihexyphenidyl 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.


Ocular side effects have included blurred vision, mydriasis, and cycloplegia. Trihexyphenidyl (the active ingredient contained in Trihexane) may also cause angle-closure glaucoma, which has rarely led to blindness.


Cardiovascular side effects have included tachycardia, although an isolated case of bradycardia has also been described. Orthostatic hypotension has been reported during withdrawal syndromes following discontinuation of long-term trihexyphenidyl (the active ingredient contained in Trihexane) therapy.


Genitourinary side effects have included urinary retention and dysuria.


Metabolic side effects have included alterations in thermal homeostasis as a result of trihexyphenidyl (the active ingredient contained in Trihexane) s inhibition of the body's sweating mechanism. Heat stroke, hyperthermia, and fever have occurred with anticholinergic agents, most commonly in patients on concomitant neuroleptic or tricyclic antidepressant therapy.


Anticholinergic poisoning syndrome may persist for more than a week's duration following trihexyphenidyl (the active ingredient contained in Trihexane) overdose. Most patients with anticholinergic intoxication require only supportive therapy of vital functions and/or discontinuation of medications. However, severely agitated, delirious, or comatose patients may be treated with physostigmine salicylate, an acetylcholinesterase inhibitor with both central and peripheral effects.

Anticholinergic intoxication may present with central and peripheral symptoms including those listed above, in addition to warm and dry skin, EKG abnormalities, insomnia, twitching or jerking movements, pantomime activity with nonexistent objects, hyperactivity, hyperreflexia, respiratory arrest, delirium, convulsions, shock and coma.

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