What the label lists and what reports show
Letermovir side effects
Letermovir's FDA label: “Most common adverse events (occurring in at least 10% of subjects in the PREVYMIS group and at a frequency at least 2% greater than placebo) are nausea, diarrhea, vomiting, peripheral edema, cough, headache, fatigue, and abdominal pain.” FAERS holds 3,121 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is cytomegalovirus infection reactivation (242 reports).
- No generic listed
Check it at the source: the letermovir FDA label on DailyMed (effective January 14, 2026, Merck Sharp & Dohme LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of PREVYMIS?The most common side effects of PREVYMIS in adults who have received a hematopoietic stem cell transplant include: nausea diarrhea vomiting swelling in your arms and legs cough headache tiredness stomach (abdominal) pain The most common side effect of PREVYMIS in adults who have received a kidney transplant is diarrhea. The side effects of PREVYMIS in children are similar to the side effects in adults. These are not all the possible side effects of PREVYMIS. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Source: FDA drug label, Merck Sharp & Dohme LLC, effective January 14, 2026 (SPL set 1b49df80-be4f-47e0-a0b7-123f3e69395b), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse events (occurring in at least 10% of subjects in the PREVYMIS group and at a frequency at least 2% greater than placebo) are nausea, diarrhea, vomiting, peripheral edema, cough, headache, fatigue, and abdominal pain.
Table 8: Trial P001 All Grade Adverse Events Reported in ≥ 10% of PREVYMIS-Treated HSCT Recipients at a Frequency at least 2% Greater than Placebo
| Adverse Events | PREVYMIS (N=373) | Placebo (N=192) |
|---|---|---|
| nausea | 27% | 23% |
| diarrhea | 26% | 24% |
| vomiting | 19% | 14% |
| peripheral edema | 14% | 9% |
| cough | 14% | 10% |
| headache | 14% | 9% |
| fatigue | 13% | 11% |
| abdominal pain | 12% | 9% |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedAdult HSCT Patients: Most common adverse events (occurring in at least 10% of subjects in the PREVYMIS group and at a frequency at least 2% greater than placebo) are nausea, diarrhea, vomiting, peripheral edema, cough, headache, fatigue, and abdominal pain. ( 6.1 ) Adult Kidney Transplant Patients: Most common adverse event (occurring in at least 10% of subjects in the PREVYMIS group and at a frequency greater than valganciclovir) is diarrhea. ( 6.1 ) Pediatric Patients: Adverse events in pediatric patients are similar to adults. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Merck Sharp & Dohme LLC at 1-877-888-4231 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Adult CMV-seropositive Recipients [R+] of an Allogeneic HSCT Prophylaxis Through Week 14 (~100 days) Post-HSCT The safety of PREVYMIS was evaluated in a Phase 3 randomized, double-blind, placebo-controlled trial (P001) in which 565 subjects were randomized and treated with PREVYMIS (N=373) or placebo (N=192) through Week 14 post-HSCT. …
Source: FDA drug label, Merck Sharp & Dohme LLC, effective January 14, 2026 (SPL set 1b49df80-be4f-47e0-a0b7-123f3e69395b), via openFDA; the full label on DailyMed
What do FAERS reports show?
3,121 reports list letermovir among the medicines taken, each a report of something that happened, not proof the medicine caused it; 580 are coded as a death and 1,223 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 17 reactions below, 2 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Letermovir: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions