Methyldopa and Ferric Ammonium Citrate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Methyldopa
Ferric Ammonium Citrate
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Decreased methyldopa effectiveness
Interaction Deep Dive
When methyldopa was given concurrently with either ferrous gluconate or ferrous sulfate, the absorption of methyldopa declined from its typical normal of 30% to an absorption of about 10%. Blood pressure also increased in patients. Parenteral iron should not alter methyldopa bioavailability13.
Why it happens (mechanism)
Decreased methyldopa absorption
Literature reports
1 report — tap to read
a) Concomitant administration of methyldopa and ferrous sulfate or ferrous gluconate resulted in a significant decrease in the proportion of methyldopa excreted as "free" drug, a significant increase in the proportion excreted as methyldopa sulfate, a decrease in the percentage of methyldopa absorbed, and an overall 88% reduction of "free" methyldopa excreted in the urine. In a subsequent study, five patients with hypertension were treated with methyldopa and ferrous sulfate for two weeks. Increases in systolic and diastolic blood pressure occurred in four patients; this resolved with withdrawal of the ferrous sulfate. These data suggest that combined chronic therapy with ferrous salts and methyldopa may reduce the hypotensive effects of the methyldopa. However, all ferrous sulfate and ferrous gluconate doses were taken simultaneously with methyldopa in this study; more studies are required to evaluate this interaction after appropriate spacing (two or more hours) of the doses is maintained 1. Formation of a ferric iron/methyldopa complex has been demonstrated in a rat-model 2.
Common questions
Can I take Methyldopa and Ferric Ammonium Citrate together?
Decreased methyldopa effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Methyldopa and Ferric Ammonium Citrate interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Methyldopa or Ferric Ammonium Citrate need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (3)
- Campbell N, Paddock V, & Sundaram R: Alteration of methyldopa absorption, metabolism, and blood pressure control caused by ferrous sulfate and ferrous gluconate. Clin Pharmacol Ther 1988; 43:381-386. PubMed
- Campbell NRC, Campbell RRA, & Hasinoff BB: Ferrous sulfate reduces methyldopa absorption: methyldopa: iron complex formation as a likely mechanism. Clin Invest Med 1990; 13:329-332.
- Lam YW & Shepherd AM: Drug interactions in hypertensive patients. Pharmacokinetic, pharmacodynamic and genetic considerations. Clin Pharmacokinet 1990; 18:295-317. DOI
Keep reading about Methyldopa
Keep reading about Ferric Ammonium Citrate
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
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