Amitriptyline and Meperidine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Amitriptyline
Meperidine
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 amitriptyline (Elavil) and meperidine (Demerol) together needs some care. Both drugs raise serotonin, a brain chemical. When two serotonin-boosting medicines are combined, there is a chance of too much serotonin, called serotonin syndrome. Signs can include agitation, confusion, a fast heartbeat, sweating, shakiness, or muscle twitching, usually showing up within hours to a few days.
Both drugs can also slow the gut and bladder, so you might notice constipation or trouble passing urine. The good news is your care team can manage this by watching you closely, especially when starting or changing doses. Keep taking both as prescribed and let your doctor or pharmacist know right away if you feel unwell.
Effect: Additive serotonergic activity raises the risk of serotonin syndrome; combined anticholinergic effects raise the risk of urinary retention, severe constipation, and potentially paralytic ileus.
Mechanism: Amitriptyline (TCA) inhibits serotonin reuptake and has strong anticholinergic properties; meperidine has serotonergic activity. Effects are pharmacodynamic and additive, not a metabolic/prodrug issue.
- Direction/magnitude: Increased serotonergic and anticholinergic burden; magnitude not quantified.
- Onset: Hours to days.
- Evidence: Theoretical; severity major.
- Management: If combined, monitor closely at initiation/titration for mental status changes, autonomic instability, neuromuscular signs, and GI/urinary symptoms. Discontinue meperidine if serotonin syndrome is suspected.
What happens
Increased risk of serotonin syndrome and an increased risk of paralytic ileus
Interaction Deep Dive
When meperidine is taken together with serotonergic drugs, such as SSRIs, serotonin and norepinephrine reuptake inhibitors, tricyclic antidepressants, triptans, 5-HT3 receptor antagonists, agents that interfere with serotonin metabolism, and other medications acting on the serotonergic system, serotonin syndrome can develop. Furthermore, combining meperidine with anticholinergic agents may heighten the likelihood of urinary retention and/or severe constipation, potentially progressing to paralytic ileus. Should concurrent administration of meperidine and serotonergic drugs be required, the patient should be monitored, particularly when therapy is being started and during dose changes. The onset of serotonin syndrome symptoms from combined use typically appears within hours to days; meperidine should be stopped if the condition is suspected. Manifestations of serotonin syndrome can involve altered mental status, autonomic instability, neuromuscular abnormalities, and/or gastrointestinal complaints, and may be fatal. Likewise, when meperidine is given alongside anticholinergic medications, watch patients for indications of urinary retention or diminished gastric motility123.
Why it happens (mechanism)
Additive serotonergic effects; additive effects on gastric motility
How to manage this interaction
If both are prescribed, your care team can manage this safely.
- Keep taking both as prescribed unless your prescriber tells you otherwise.
- Your team will watch you more closely, especially when starting either drug or changing the dose.
- Doses may be adjusted and individualized by your care team.
- Watch for serotonin syndrome signs: agitation, confusion, fast heartbeat, sweating, shivering, muscle twitching, or fever, usually within hours to days.
- Also watch for constipation or trouble urinating.
- Contact your prescriber or pharmacist right away, or seek urgent care, if these symptoms appear.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
Common questions
Can I take Amitriptyline and Meperidine together?
Combining amitriptyline and meperidine can add up to too much serotonin and can slow your gut and bladder, so stay alert for symptoms and let your care team monitor you, especially when starting or adjusting doses. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Amitriptyline and Meperidine 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 Amitriptyline and Meperidine interaction managed?
If both are prescribed, your care team can manage this safely. Keep taking both as prescribed unless your prescriber tells you otherwise. Your team will watch you more closely, especially when starting either drug or changing the dose. Doses may be adjusted and individualized by your care team. Watch for serotonin syndrome signs: agitation, confusion, fast heartbeat, sweating, shivering, muscle tw… 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 Amitriptyline or Meperidine 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: MEPERGAN intramuscular, intravenous injection, meperidine HCl, promethazine HCl intramuscular, intravenous injection. West-Ward Pharmaceuticals Corp (per FDA), Eatontown, NJ, 2023.
- Product Information: DEMEROL(R) oral tablets, oral solution, meperidine HCl oral tablets, oral solution. Validus Pharmaceuticals LLC (per FDA), Parsippany, NJ, 2023. DailyMed
- Product Information: Demerol(TM) intramuscular, subcutaneous, intravenous injection, meperidine HCl intramuscular, subcutaneous, intravenous injection. Hospira Inc (per FDA), Lake Forest, IL, 2022.
Keep reading about Amitriptyline
Keep reading about Meperidine
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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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