Methyldopa and Phenylpropanolamine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Methyldopa
Phenylpropanolamine
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
Hypertension
Interaction Deep Dive
Concomitant phenylpropanolamine and methyldopa therapy has been reported to result in a severe hypertensive reaction1.
Why it happens (mechanism)
Alpha adrenergic potentiation
Literature reports
1 report — tap to read
a) A severe hypertensive reaction occurred in a patient that was well-controlled on methyldopa and oxprenolol two days after beginning therapy with a cold preparation containing phenylpropanolamine and acetaminophen 1.
Common questions
Can I take Methyldopa and Phenylpropanolamine together?
Hypertension Always confirm with your pharmacist or prescriber before making any change.
How serious is the Methyldopa and Phenylpropanolamine interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
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 Phenylpropanolamine 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 (1)
- McLaren EH: Severe hypertension produced by interaction of phenylpropanolamine with methyldopa and oxprenolol. Br Med J 1976; 2:283-284. DOI
Keep reading about Methyldopa
Keep reading about Phenylpropanolamine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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