What the FDA labels say about taking them together
Metoprolol and quinine
Quinine's FDA label of November 9, 2023 names metoprolol in its drug interactions (prescription label) section; the metoprolol labels PlainMeds reads (4) do not name quinine.
Check it at the source: the metoprolol FDA label on DailyMed (effective March 3, 2026, Melinta Therapeutics, LLC); the quinine FDA label on DailyMed (effective November 9, 2023).
What does the metoprolol label say about quinine?
Metoprolol's label (effective March 3, 2026) and its 3 other brand-application labels do not name quinine in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (TOPROL XL), Melinta Therapeutics, LLC, effective March 3, 2026 (SPL set 496ddfaa-7c9c-4888-b747-a210249b367a), via openFDA; the full label on DailyMed
What does the quinine label say about metoprolol?
Quinine label, drug interactions (prescription label)Although clinical drug interaction studies have not been performed, antimalarial doses (greater than or equal to 600 mg) of quinine may inhibit the metabolism of other drugs that are CYP2D6 substrates (e.g., flecainide, debrisoquine, dextromethorphan, metoprolol, paroxetine ).
Source: FDA drug label (Chininum sulphuricum), Boiron, effective November 9, 2023 (SPL set 33885950-2a55-11e7-8288-424c58303031), 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
| Metoprolol | Quinine | |
|---|---|---|
| Labeled for | High blood pressure, Angina, Heart failure, Heart attack and coronary artery disease | n/a |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.085 per tablet 100 mg tablet | $0.698 per capsule 324 mg capsule |
| Shortage now | A presentation being discontinued | 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