Hypersensitivity to the active substance or to any of the excipients listed in Description.
Concomitant administration with pimozide (see Precautions and Interactions).
Concomitant administration with ergot alkaloids (see Precautions and Interactions).
Concomitant administration with St. John's wort (Hypericum perforatum) (see Interactions).
When letermovir is combined with cyclosporine: Concomitant use of dabigatran, atorvastatin, simvastatin, rosuvastatin or pitavastatin is contraindicated (see Interactions).