Acetaminophen And Codeine and Metolazone: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jun 30, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Metolazone
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's going on: Metolazone is a water pill (diuretic) that helps your body get rid of extra fluid and can help lower blood pressure. The codeine in your pain medicine may make your body hold onto more water by triggering a hormone that keeps fluid in. That could make the water pill work a little less well.
This is a theoretical concern, meaning it is based on how these drugs work rather than strong studies. Keep taking both exactly as prescribed. Watch for swelling in your legs, weight gain, or blood pressure that creeps up, and let your care team know. They can adjust your water pill dose and keep an eye on things.
Effect: Possible reduced diuretic efficacy of metolazone when combined with codeine (acetaminophen/codeine).
Mechanism: Opioid-mediated increase in antidiuretic hormone (ADH) release, promoting water retention and counteracting metolazone's natriuretic/diuretic effect. Codeine is a prodrug (CYP2D6 to morphine), but this is a pharmacodynamic, not metabolic, interaction. Direction: reduced diuretic response.
Evidence: Theoretical; onset unspecified; severity rated major.
- Monitor urine output, edema, weight, and blood pressure.
- Titrate/individualize metolazone dose as clinically indicated if diuresis appears blunted.
What happens
Reduced diuretic efficacy
Interaction Deep Dive
Taking codeine together with diuretics can diminish the therapeutic effect of the diuretics because it triggers the secretion of anti-diuretic hormone. Watch for indications of reduced diuresis and/or changes in blood pressure, and raise the diuretic dose when necessary1.
Why it happens (mechanism)
Increased opioid-mediated release of antidiuretic hormone
How to manage this interaction
Keep taking both medications as prescribed unless your prescriber tells you otherwise. This concern is theoretical, and your care team can manage it.
- Watch for signs the water pill isn't working as well: new or worse swelling in the ankles or legs, rapid weight gain, or higher blood pressure readings.
- Report these to your pharmacist or doctor.
- Your metolazone dose may need to be adjusted and individualized by your care team, and they may monitor your blood pressure and fluid status more closely while you use both.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Metolazone together?
Codeine may slightly weaken metolazone's water-pill effect by triggering a fluid-retaining hormone. Keep taking both as prescribed, watch for swelling or rising blood pressure, and let your care team adjust the diuretic dose if needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Metolazone interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Acetaminophen And Codeine and Metolazone interaction managed?
Keep taking both medications as prescribed unless your prescriber tells you otherwise. This concern is theoretical, and your care team can manage it. Watch for signs the water pill isn't working as well: new or worse swelling in the ankles or legs, rapid weight gain, or higher blood pressure readings. Report these to your pharmacist or doctor. Your metolazone dose may need to be adjusted and indiv… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Acetaminophen And Codeine or Metolazone 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 a safer alternative to one of these medications for me?
References (1)
- Product Information: CARISOPRODOL, ASPIRIN, CODEINE PHOSPHATE oral tablets, carisoprodol, aspirin, codeine phosphate oral tablets. Ingenus Pharmaceuticals LLC (per DailyMed), Orlando, FL, 2021. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Metolazone
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