I'm sure it is from the medication. Tell him he needs to tell his doctor about this.
♡Princess
Hello,
Medications such as blood pressure medications (especially beta-blockers), heart medications (such as digoxin), some peptic ulcer medications, sleeping pills, and antidepressants may also cause erectile dysfunction. Erectile dysfunction is not a reported side effect of Valtrex.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.