Primidone and Acetaminophen And Codeine: 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
Primidone
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.
Taking your acetaminophen with codeine together with primidone can pull in two directions. Both medicines can slow down your brain and breathing, so combining them can make you very drowsy, dizzy, or short of breath. That is the part to watch most closely.
At the same time, primidone can speed up how your body breaks down codeine, which may make the codeine work less well for pain. Here is the tricky part: if primidone is ever stopped, the codeine level can climb and hit harder. Please don't change either medicine on your own. Your care team can manage this safely by picking the right doses and keeping an eye on you.
Effect: Additive CNS/respiratory depression plus reduced codeine efficacy when combined with primidone (metabolized in part to phenobarbital).
- Mechanism: Additive CNS depression (PD); phenobarbital-driven CYP3A4 induction increases codeine metabolism, lowering parent codeine exposure (PK).
- Direction: Increased sedation/respiratory depression risk; decreased analgesic efficacy over time.
- Onset/evidence: Unspecified onset; theoretical, rated major.
- Management: Reserve for when alternatives are inadequate. Use lowest effective dose and shortest duration. Monitor for respiratory depression, hypotension, sedation, and opioid withdrawal. On primidone discontinuation, anticipate rising codeine levels and enhanced opioid effects.
What happens
Increased risk of CNS depression and reduced codeine exposure
Interaction Deep Dive
Taking codeine alongside phenobarbital, or its prodrug primidone, can produce respiratory depression, hypotension, and pronounced sedation, with the possibility of coma or death. This combination may also lessen the effectiveness of codeine. When the two must be given together, watch for indications of respiratory depression or opioid withdrawal and weigh dose modifications. If phenobarbital or primidone is stopped, codeine plasma levels will rise, which can heighten or extend both the therapeutic and adverse effects of codeine, including the danger of serious respiratory depression2. Restrict combined prescribing of these agents to patients whose alternative treatment options are insufficient. Keep doses and durations to the lowest amount needed. Monitor patients closely for evidence of respiratory depression and sedation 13.
Why it happens (mechanism)
Additive CNS depression; induction of CYP3A4-mediated metabolism of codeine
How to manage this interaction
Keep taking both exactly as prescribed unless your prescriber tells you otherwise. This combination is usually reserved for when other options aren't enough, at the lowest dose for the shortest time needed.
- Your team may monitor you more closely for heavy sedation, slow or shallow breathing, dizziness, or low blood pressure.
- Doses may need to be adjusted and individualized by your care team.
- Tell your prescriber if the codeine seems to stop working for pain.
- Flag it if primidone is ever stopped or changed, since your codeine effect could increase.
- Seek urgent help for very slow breathing or extreme drowsiness.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Primidone and Acetaminophen And Codeine together?
Combining acetaminophen with codeine and primidone can increase dangerous sedation and slowed breathing while also making codeine less effective, so use both only under close medical supervision and never adjust either on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Primidone and Acetaminophen And Codeine 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 Primidone and Acetaminophen And Codeine interaction managed?
Keep taking both exactly as prescribed unless your prescriber tells you otherwise. This combination is usually reserved for when other options aren't enough, at the lowest dose for the shortest time needed. Your team may monitor you more closely for heavy sedation, slow or shallow breathing, dizziness, or low blood pressure. Doses may need to be adjusted and individualized by your care team. Tell… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Primidone or Acetaminophen And Codeine 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 (3)
- Product Information: CARISOPRODOL, ASPIRIN, CODEINE PHOSPHATE oral tablets, carisoprodol, aspirin, codeine phosphate oral tablets. Ingenus Pharmaceuticals LLC (per DailyMed), Orlando, FL, 2021. DailyMed
- Product Information: codeine sulfate oral tablets, codeine sulfate oral tablets. West-Ward Pharmaceuticals Corp. (per FDA), Eatontown, NJ, 2017. DailyMed
- Product Information: SEZABY(TM) intravenous injection, phenobarbital sodium intravenous injection. Sun Pharmaceutical Industries Inc (per manufacturer), Cranbury, NJ, 2022. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Primidone
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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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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