Acetaminophen And Codeine and Methyclothiazide: 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
Methyclothiazide
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.
You've been prescribed acetaminophen with codeine (a pain reliever) along with methyclothiazide (a water pill, or diuretic, that helps your body get rid of extra fluid). The concern here is that codeine may cause your body to hold onto more water by triggering a hormone that keeps fluid in. That could make your water pill work a little less well, so you might not lose as much fluid and your blood pressure may not be controlled as well.
The good news is that this is based on theory more than strong real-world evidence. Please keep taking both medicines as prescribed. Your care team can watch how well the water pill is working and adjust things if needed.
Effect: Codeine may reduce the diuretic efficacy of methyclothiazide (a thiazide diuretic).
Mechanism: Opioid-mediated stimulation of antidiuretic hormone (ADH) release promotes water retention, opposing the natriuretic/diuretic action. This is a PD interaction; codeine's analgesic activity is via CYP2D6 conversion to morphine, but the diuretic interaction is independent of that.
- Direction: reduced diuretic/antihypertensive response
- Onset: unspecified
- Evidence: theoretical
- Management: Monitor urine output, weight/edema, and blood pressure. Titrate the diuretic dose as clinically indicated and individualize per response.
What happens
Reduced diuretic efficacy
Interaction Deep Dive
Taking codeine together with diuretics can diminish diuretic effectiveness because codeine may stimulate the secretion of anti-diuretic hormone. Watch patients for indications of reduced diuresis and/or changes in blood pressure, and raise the diuretic dose when required1.
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 interaction is theoretical, but it's worth being aware of.
- Your care team may monitor how well your water pill is working, watching for less urination, swelling in your legs or ankles, weight gain, or blood pressure that isn't well controlled.
- The diuretic dose may need to be adjusted and individualized by your team if they see reduced effect.
- Tell your pharmacist or doctor if you notice new swelling, sudden weight gain, or blood pressure changes.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Methyclothiazide together?
Codeine may slightly weaken how well your water pill (methyclothiazide) works by causing fluid retention, but this is theoretical. Keep taking both as prescribed and let your care team monitor and adjust your diuretic dose if needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Methyclothiazide 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 Methyclothiazide interaction managed?
Keep taking both medications as prescribed unless your prescriber tells you otherwise. This interaction is theoretical, but it's worth being aware of. Your care team may monitor how well your water pill is working, watching for less urination, swelling in your legs or ankles, weight gain, or blood pressure that isn't well controlled. The diuretic dose may need to be adjusted and individualized by… 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 Methyclothiazide 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 Methyclothiazide
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