Drug interactions
Olanzapine + Trihexyphenidyl
Severity: Moderate
Olanzapine and Trihexyphenidyl: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Both drugs have anticholinergic activity, so combined use can cause additive effects such as dry mouth, constipation, urinary retention, blurred vision, confusion and tachycardia. Elderly patients are at particular risk of delirium and ileus.
What this interaction means in plain words
Olanzapine and Trihexyphenidyl can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Olanzapine belongs to Central Nervous System; Trihexyphenidyl belongs to Central Nervous System.
Why it happens
Additive antimuscarinic pharmacodynamic effects.
What to do
Use the lowest effective trihexyphenidyl dose and review its ongoing need. Monitor for cognitive effects, constipation and urinary retention.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Olanzapine
Other interactions of Trihexyphenidyl
Frequently asked questions
Can I take Olanzapine with Trihexyphenidyl?
MediHelp rates the interaction as moderate. Olanzapine and Trihexyphenidyl can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Both drugs have anticholinergic activity, so combined use can cause additive effects such as dry mouth, constipation, urinary retention, blurred vision, confusion and tachycardia. Elderly patients are at particular risk of delirium and ileus.
How serious is the interaction between Olanzapine and Trihexyphenidyl?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use the lowest effective trihexyphenidyl dose and review its ongoing need. Monitor for cognitive effects, constipation and urinary retention.
What other medicines interact with Olanzapine?
MediHelp also lists interactions of Olanzapine with, for example, Amisulpride, Amoxapine, Apomorphine. The full list is on the Olanzapine page.
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