What the FDA labels say about taking them together
Isoniazid and levodopa
Levodopa's FDA label of July 20, 2026 names isoniazid in its drug interactions section; the isoniazid label PlainMeds reads does not name levodopa. The levodopa label: “DRUG INTERACTIONS Monitor patients on MAO-B inhibitors for orthostatic hypotension Dopamine D2 antagonists, isoniazid, and iron salts:”
Check it at the source: the isoniazid FDA label on DailyMed (effective July 8, 2025, OMNIVIUM PHARMACEUTICALS LLC.); the levodopa FDA label on DailyMed (effective July 20, 2026, Merz Pharmaceuticals, LLC).
What does the isoniazid label say about levodopa?
Isoniazid's label (effective July 8, 2025) does not name levodopa in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (isoniazid), OMNIVIUM PHARMACEUTICALS LLC., effective July 8, 2025 (SPL set 35400f1d-fd25-4bfa-a382-ac390e21bf2e), via openFDA; the full label on DailyMed
What does the levodopa label say about isoniazid?
Levodopa label, drug interactionsDRUG INTERACTIONS Monitor patients on MAO-B inhibitors for orthostatic hypotension ( 7.1 ) Dopamine D2 antagonists, isoniazid, and iron salts:
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
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
| Isoniazid | Levodopa | |
|---|---|---|
| Labeled for | n/a | Parkinson's disease |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $3.40 per tablet 300 mg tablet | n/a |
| 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