Letermovir Injection and Flibanserin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Flibanserin
Letermovir Injection
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.
What happens
Increased flibanserin exposure and an increased flibanserin-related adverse effects
Interaction Deep Dive
Concomitant use of flibanserin, a CYP3A4 substrate, and a strong or moderate CYP3A4 inhibitor increases flibanserin exposure, which may result in hypotension, syncope, or CNS depression (eg, sedation, somnolence). In pharmacokinetic studies, coadministration of flibanserin with the strong CYP3A4 inhibitors, ketoconazole and itraconazole increased flibanserin exposure by 4.5-fold and 2.6-fold, respectively. Coadministration of flibanserin with fluconazole (a moderate CYP3A4 inhibitor, moderate CYP2C9 inhibitor, and a strong CYP2C19 inhibitor) and grapefruit juice (moderate CYP3A4 inhibitors) increased flibanserin exposure by 7-fold and 1.4-fold, respectively. In the studies of ketoconazole and fluconazole, more subjects who received flibanserin concomitantly with the CYP3A4 inhibitor experienced hypotension or syncope compared with those who received flibanserin or the CYP3A4 inhibitor alone. Therefore, concurrent use of flibanserin with a strong or moderate CYP3A4 inhibitor is contraindicated. If coadministration is required, flibanserin should be discontinued at least 2 days before initiating the strong or moderate CYP3A4 inhibitor. In addition, the strong or moderate CYP3A4 inhibitor should be discontinued for 2 weeks prior to initiating or restarting flibanserin1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of flibanserin
Literature reports
4 reports — tap to read
a) In a pharmacokinetic study of 24 healthy female subjects, coadministration of a single 50-mg dose of flibanserin with ketoconazole (a strong CYP3A4 inhibitor) 400 mg given once daily for 5 days following a light breakfast increased flibanserin AUC(0 to infinity) a significant 4.5-fold and Cmax a significant 1.8-fold compared with flibanserin 50 mg administered alone. Syncope was reported in 1 of 24 (4%) subjects who received concomitant flibanserin and ketoconazole, in 1 of 24 (4%) subjects who received flibanserin alone, and in no subjects who received ketoconazole alone in this study 1.
b) In a pharmacokinetic study of 12 healthy male and female subjects, coadministration of a single 50-mg dose of flibanserin given 2 hours after 5 days of itraconazole (a strong CYP3A4 inhibitor) 400 mg loading dose followed by 4 days of 200 mg once daily increased flibanserin AUC (0 to infinity) a significant 2.6-fold and Cmax a significant 1.7-fold compared with flibanserin 50 mg alone. The 200-mg itraconazole dose does not maximally inhibit the CYP3A4 enzyme 1.
c) In a pharmacokinetic study of 15 healthy female subjects, coadministration of a single 100-mg dose of flibanserin with fluconazole (a moderate CYP3A4 inhibitor, moderate CYP2C9 inhibitor, and a strong CYP2C19 inhibitor) 400-mg loading dose followed by 200 mg once daily for 5 days increased flibanserin AUC(0 to infinity) a significant 7-fold and Cmax a significant 2.2-fold compared with flibanserin 100 mg alone. The study was stopped early, because 3 of 15 subjects (20%) who received concomitant fluconazole and flibanserin experienced hypotension or syncope requiring a supine position with legs elevated compared with no such events in subjects treated with flibanserin or fluconazole alone. One of these 3 subjects became unresponsive with a blood pressure of 64/41 mmHg and required treatment with IV saline in the hospital emergency department 1.
d) In a pharmacokinetic study of 26 healthy female subjects, coadministration of a single 100 mg dose of flibanserin with 240 mL of grapefruit juice (a moderate CYP3A4 inhibitor) increased flibanserin AUC(0 to infinity) by 1.4-fold and Cmax 1.1-fold compared with flibanserin 100 mg alone 1.
Common questions
Can I take Letermovir Injection and Flibanserin together?
Increased flibanserin exposure and an increased flibanserin-related adverse effects Always confirm with your pharmacist or prescriber before making any change.
How serious is the Letermovir Injection and Flibanserin interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Letermovir Injection or Flibanserin 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: ADDYI(R) oral tablets, flibanserin oral tablets. Sprout Pharmaceuticals Inc (per FDA), Raleigh, NC, 2021. DailyMed
Keep reading about Flibanserin
Keep reading about Letermovir Injection
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