Medically reviewed by Holly McCain. Last updated on August 14, 2025
Wyeth-Ayerst
Trihexyphenidyl HCl
Antispasmodic
Indications And Clinical Uses: As an adjunct in the treatment of all forms of parkinsonism (postencephalitic, arteriosclerotic, and idiopathic). It is often useful as adjuvant therapy when treating these forms of parkinsonism with levodopa. Additionally, it is indicated for the control of extrapyramidal disorders caused by central nervous system drugs such as the dibenzoxazepines, phenothiazines, thioxanthenes, and butyrophenones.
Manufacturers’ Warnings In Clinical States: Patients to be treated with trihexyphenidyl should have a gonioscope evaluation and close monitoring of intraocular pressures at regular periodic intervals.
Precautions: Maintain patients with cardiac, liver, kidney or hypertensive disorders under close observation. Patients undergoing prolonged therapy should be subjected to constant and careful long-term observation to avoid allergic and other untoward reactions. Trihexyphenidyl should be used with caution in patients with glaucoma, obstructive disease of the gastrointestinal or genitourinary tracts, and in elderly males with possible prostatic hypertrophy. Geriatric patients, particularly over the age of 60, frequently develop increased sensitivity to parasympatholytic drugs and hence, require strict dosage regulation. Incipient glaucoma may be precipitated by trihexyphenidyl. Tardive dyskinesia may appear in some patients on long-term therapy with antipsychotic drugs or may occur after therapy with these drugs has been discontinued. Antiparkinsonism agents do not alleviate the symptoms of tardive dyskinesia, and in some instances may aggravate them. However, parkinsonism and tardive dyskinesia often coexist in patients receiving chronic neuroleptic treatment, and anticholinergic therapy with trihexyphenidyl may relieve some of these parkinsonism symptoms.
Adverse Reactions: Dryness of mouth, blurred vision, dizziness, mild nausea or nervousness will be experienced by 30 to 50% of all patients. These sensations, however, are much less troublesome with trihexyphenidyl than with belladonna alkaloids and are usually less disturbing than unalleviated parkinsonism. Such reactions tend to become less pronounced, and even to disappear, as treatment continues. Even before these reactions have remitted spontaneously, they may often be controlled by careful adjustment of dosage form, amount of drug, or interval between doses.
Isolated instances of suppurative parotitis secondary to excessive dryness of the mouth, skin rashes, dilatation of the colon, paralytic ileus, and certain psychiatric manifestations such as delusions and hallucinations, plus one doubtful case of paranoia have been rarely reported with trihexyphenidyl.
Patients with arteriosclerosis or with a history of idiosyncrasy to other drugs may exhibit reactions of mental confusion, agitation, disturbed behavior, or nausea and vomiting. Such patients should be allowed to develop a tolerance through the initial administration of a small dose and gradual increase in dose until an effective level is reached. If a severe reaction should occur, administration of the drug should be discontinued for a few days and then resumed at a lower dosage. Psychiatric disturbances can result from indiscriminate use (leading to overdosage) to sustain continued euphoria.
Potential untoward effects associated with the use of any atropine like drugs include constipation, drowsiness, urinary hesitancy or retention, tachycardia, dilatation of the pupil, increased intraocular tension, weakness, vomiting, and headache.
The occurrence of angle closure glaucoma due to long term trihexyphenidyl treatment has been reported.
Dosage And Administration: Should be individualized. The initial dosage should be low and then increased gradually, especially in patients over 60 years of age.
Whether trihexyphenidyl may best be given before or after meals should be determined by the way the patient reacts. Postencephalitic patients, who are usually more prone to excessive salivation, may prefer to take it after meals and may, in addition, require small amounts of atropine which, under such circumstances, is sometimes an effective adjuvant. If trihexyphenidyl tends to dry the mouth excessively, it may be better to take it before meals, unless it causes nausea. If taken after meals, the thirst sometimes induced can be allayed by mint candies, chewing gum or water.
Parkinsonism: 1 mg orally the first day; increased by 2 mg daily at intervals of 3 to 5 days, up to 6 to 10 mg daily. Best tolerated in divided doses at mealtime.
Drug Induced Parkinsonism: The size and frequency of doses of trihexyphenidyl HCl needed to control drug induced extrapyramidal reactions notably reserpine, and phenothiazine derivatives, must be determined empirically. The total daily dosage usually ranges between 5 and 15 mg although, in some cases, these reactions have been satisfactorily controlled on as little as 1 mg daily. It may be advisable to commence therapy with a single 1 mg dose. If the extrapyramidal manifestations are not controlled in a few hours, the subsequent doses may be progressively increased until satisfactory control is achieved. Satisfactory control may sometimes be more rapidly achieved by temporarily reducing the dosage of the tranquilizer or instituting trihexyphenidyl HCl therapy and then adjusting dosage of both drugs until the desired ataractic effect is retained without onset of the extrapyramidal reactions.
It is sometimes possible to maintain the patient on a reduced trihexyphenidyl HCl dosage after the reactions have remained under control for several days. Instances have been reported in which these reactions have remained in remission for long periods after therapy was discontinued.
Concomitant use of trihexyphenidyl with levodopa: When trihexyphenidyl is used concomitantly with levodopa, the usual dose of each may need to be reduced. Careful adjustment is necessary, depending on side effects and degree of symptom control. Trihexyphenidyl dosage of 3 to 6 mg daily, in divided doses, is usually adequate.
Concomitant use of trihexyphenidyl with other parasympathetic inhibitors: Trihexyphenidyl may be substituted, whole or in part, for other parasympathetic inhibitors. The usual technique is partial substitution initially, with progressive reduction in the other medication as the dose of trihexyphenidyl is increased.
The total daily intake of tablets or elixir is tolerated best if divided into 3 doses and taken at mealtimes. High doses (>10 mg daily) may be divided into 4 parts with 3 doses administered at mealtimes and the fourth at bedtime.
Availability And Storage: Elixir: Each 5 mL of clear, lime flavored preparation contains: trihexyphenidyl HCl 2 mg with methylparaben 4 mg, propylparaben 1 mg, citric acid 9 mg and alcohol 214 mg as preservatives. Tartrazine-free. Bottles of 450 mL.
Tablets: 2 mg: Each round, white, scored tablet, engraved “LL, A11” and “Artane 2”, contains: trihexyphenidyl HCl 2 mg. Tartrazine-free. Bottles of 100.
5 mg: Each round, white, scored tablet, engraved “LL, A12” and “Artane 5”, contains: trihexyphenidyl HCl 5 mg. Tartrazine-free. Bottles of 100.
Reviewed 1995