Cyclobenzaprine and Amitriptyline: 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
Cyclobenzaprine
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.
These two medicines can stack up similar side effects. Amitriptyline (Elavil) is an antidepressant, and cyclobenzaprine is a muscle relaxer. They are actually chemical cousins, so taking them together can add up their effects. You might notice more dry mouth, blurry vision, constipation, trouble urinating, or a fast heartbeat. There is also a small chance of a rare but serious reaction called serotonin syndrome (things like agitation, sweating, shaking, or a racing heart), and both drugs can affect your heart's rhythm.
Please don't stop either medicine on your own. Your doctor or pharmacist can watch you closely, adjust doses, and make sure this combination stays safe for you.
Additive toxicity between two structurally related agents. Amitriptyline (anticholinergic TCA) and cyclobenzaprine share overlapping pharmacology, giving additive risk across three domains:
- Anticholinergic (atropine-like): dry mouth, urinary retention, constipation, tachycardia, confusion.
- Serotonergic: potential serotonin syndrome (mental status change, autonomic instability, neuromuscular findings).
- QT prolongation: additive effect on the QT interval.
Mechanism largely additive/pharmacodynamic; neither drug's clearance drives this. Evidence is theoretical, severity rated major, onset unspecified. Management: use caution, observe closely at initiation and dose increases, consider ECG monitoring where QT risk factors exist, and discontinue if serotonin syndrome emerges with supportive care.
What happens
An increased risk of atropine-like adverse reactions, an increased risk of serotonin syndrome and an increased risk of QT interval prolongation
Interaction Deep Dive
Caution is warranted when cyclobenzaprine is given together with anticholinergic TCA's that prolong the QT interval, since this combination may heighten the likelihood of serotonergic syndrome as well as the likelihood of atropine-like adverse reactions. When cyclobenzaprine is paired with other serotonergic agents, a serotonin syndrome that can be life threatening may develop. Should signs of serotonin syndrome arise while other serotonergic drugs are being used, cyclobenzaprine should be stopped without delay and supportive symptomatic care begun. In cases where combining cyclobenzaprine with other serotonergic drugs is clinically justified, close monitoring is recommended, especially when therapy is started or the dose is raised. Manifestations of serotonin syndrome can encompass altered mental status (for example, confusion, agitation, hallucinations), autonomic instability (for example, diaphoresis, tachycardia, labile blood pressure, hyperthermia), neuromuscular disturbances (for example, tremor, ataxia, hyperreflexia, clonus, muscle rigidity), and/or gastrointestinal complaints (for example, nausea, vomiting, diarrhea)1. Giving cyclobenzaprine alongside another agent that prolongs the QT interval can produce additive QT prolongation21.
Why it happens (mechanism)
Unknown; additive serotonergic effect; additive QT interval prolongation
How to manage this interaction
The good news is your care team can manage this. Keep taking both exactly as prescribed unless your prescriber tells you otherwise.
- Your team may individualize your doses and watch you more closely, especially when starting either drug or raising a dose.
- They may check your heart rhythm (an ECG) if you have other heart-rhythm risk factors.
- Tell them right away about confusion, agitation, heavy sweating, tremor, muscle stiffness, a racing or irregular heartbeat, fever, or nausea and diarrhea, which can signal serotonin syndrome.
- Mention bothersome dry mouth, constipation, or trouble urinating.
Ask your pharmacist to review the combination and whether an alternative is worth discussing.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) Cases reported after marketing have described serotonin syndrome occurring when oral cyclobenzaprine was used together with other agents, including SSRIs, SNRIs, TCAs, traMADol, buPROPion, meperidine, verapamil, or MAO inhibitors 1.
b) A woman aged 59 experienced torsade de pointes that advanced to ventricular fibrillation and cardiac arrest after being given droPERidol during elective Achilles tendon surgery, one day after stopping cyclobenzaprine. Five days before the operation, her QTc was prolonged at 497 milliseconds (msec), while magnesium and potassium levels were within normal ranges. Her home medications, stopped the day before surgery, consisted of cyclobenzaprine 10 mg/day and FLUoxetine 30 mg/day, along with amLODIPine, diclofenac, and triamterene/hydroCHLOROthiazide. She received premedication 45 minutes before surgery consisting of droPERidol 0.625 mg IV and metoclopramide 10 mg IV. Roughly 1 hour and 45 minutes after the surgery began, the patient developed ventricular tachycardia consistent with torsade de pointes, which progressed to ventricular fibrillation and cardiac arrest. Right after cardioversion, her QTc measured 500 msec with no signs of ischemic injury. By postoperative day 1, her QT interval had returned to 440 msec, a value below her baseline, and an ECG demonstrated normal sinus rhythm. The patient had no known cardiac disease history and no evidence of risk factors linked to torsade de pointes or other dysrhythmias. All medications taken before admission were resumed at discharge, except for cyclobenzaprine 2.
Common questions
Can I take Cyclobenzaprine and Amitriptyline together?
Amitriptyline and cyclobenzaprine can add up anticholinergic effects, QT prolongation, and a small risk of serotonin syndrome, so take both only under supervision and report symptoms like confusion, sweating, tremor, or a racing heart promptly. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Cyclobenzaprine and Amitriptyline 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 Cyclobenzaprine and Amitriptyline interaction managed?
The good news is your care team can manage this. Keep taking both exactly as prescribed unless your prescriber tells you otherwise. Your team may individualize your doses and watch you more closely, especially when starting either drug or raising a dose. They may check your heart rhythm (an ECG) if you have other heart-rhythm risk factors. Tell them right away about confusion, agitation, heavy swe… 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 Cyclobenzaprine or Amitriptyline 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 (2)
- Product Information: TONMYA(TM) sublingual tablets, cyclobenzaprine HCl sublingual tablets. Tonix Pharmaceuticals, Inc (per manufacturer), Chatham, NJ, 2025. DailyMed
- Michalets EL, Smith LK, & Van Tassel ED: Torsade de Pointes resulting from the addition of droperidol to an existing cytochrome P450 drug interaction. Ann Pharmacother 1998; 32:761-765. PubMed
Keep reading about Amitriptyline
Keep reading about Cyclobenzaprine
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