What the FDA labels say about taking them together
Levodopa and trihexyphenidyl
Trihexyphenidyl's FDA label of October 25, 2019 names levodopa in its drug interactions section; the levodopa label PlainMeds reads does not name trihexyphenidyl. The trihexyphenidyl label: “The usual dose of either trihexyphenidyl or levodopa may need to be reduced during concomitant therapy, since concomitant administration may increase drug-induced involuntary movements.”
Check it at the source: the levodopa FDA label on DailyMed (effective July 20, 2026, Merz Pharmaceuticals, LLC); the trihexyphenidyl FDA label on DailyMed (effective October 25, 2019, Natco Pharma Limited).
What does the levodopa label say about trihexyphenidyl?
Levodopa's label (effective July 20, 2026) does not name trihexyphenidyl in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Inbrija), Merz Pharmaceuticals, LLC, effective July 20, 2026 (SPL set 077c0f39-a3a2-4b2b-a184-09131889dcfb), via openFDA; the full label on DailyMed
What does the trihexyphenidyl label say about levodopa?
Trihexyphenidyl label, drug interactionsThe usual dose of either trihexyphenidyl or levodopa may need to be reduced during concomitant therapy, since concomitant administration may increase drug-induced involuntary movements ( see DOSAGE AND ADMINISTRATION ).
Source: FDA drug label (Trihexyphenidyl Hydrochloride), Natco Pharma Limited, effective October 25, 2019 (SPL set b7e4200c-feff-4537-aad1-cf9989fd8c14), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Levodopa | Trihexyphenidyl | |
|---|---|---|
| Labeled for | Parkinson's disease | Parkinson's disease |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.0884 per tablet 2 mg tablet |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once