Drug Interaction Report

Lemborexant and Letermovir Injection: Interaction Details

A pharmacist-reviewed analysis of the Lemborexant and Letermovir Injection interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Lemborexant

Dayvigo
+

Letermovir Injection

Prevymis Prevymis®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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.

Of 67 documented Lemborexant interactions, 66 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

Increased lemborexant exposure and an increased risk of lemborexant-related adverse reactions

Interaction Deep Dive

Avoid concomitant use of lemborexant with a strong or moderate CYP3A inhibitor, as coadministration significantly increases lemborexant AUC and Cmax which may increase the risk of lemborexant-associated adverse reactions1.

Why it happens (mechanism)

Inhibition of CYP3A-mediated metabolism of lemborexant

Literature reports

2 reports — tap to read

a) Concomitant use of fluconazole increased lemborexant Cmax and AUC by approximately 1.6- and 4.2-fold, respectively which is expected to increase risk of adverse reactions, such as somnolence 23.

b) In a physiologically-based pharmacokinetic modeling study, coadministration of lemborexant with itraconazole (strong CYP3A inhibitor) or fluconazole (moderate CYP3A inhibitor) had a significantly increased effect on the Cmax and AUC of lemborexant 1.

Common questions

Can I take Lemborexant and Letermovir Injection together?

Increased lemborexant exposure and an increased risk of lemborexant-related adverse reactions Always confirm with your pharmacist or prescriber before making any change.

How serious is the Lemborexant and Letermovir Injection 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 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 Lemborexant or Letermovir Injection 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)

  1. Product Information: DAYVIGO(R) oral tablets, lemborexant oral tablets. Eisai Inc (per FDA), Nutley, NJ, 2025. DailyMed
  2. Product Information: DIFLUCAN(R) intravenous injection, fluconazole intravenous injection. Roerig (per FDA), New York, NY, 2024. DailyMed
  3. Product Information: DIFLUCAN(R) oral tablets, suspension, fluconazole oral tablets, suspension. Roerig (per FDA), New York, NY, 2024. DailyMed
Was this write-up helpful?
Lemborexant

Keep reading about Lemborexant

All Lemborexant interactions (67)
Also serious with: Estradiol Topical Atorvastatin Olaparib Istradefylline
Letermovir Injection

Keep reading about Letermovir Injection

All Letermovir Injection interactions (346) Letermovir Injection drug information
Also serious with: Lomitapide Pimozide Dihydroergotamine Bromocriptine
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Lemborexant + 1,4-butanediol Activated Charcoal Beer Gamma-hydroxybutyrate (ghb) Grapefruit Kava L-tryptophan St. John's Wort + 187 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.