Does long term once a day Acyclovir as preventative cause cancer?

[Concerned103]

I have been on Acyclovir once a day 400mg as a preventative for outbreaks for almost 2 years now. It has significantly helped lessen the amount of outbreaks as well as the duration if I do get one. I had to recently switch doctors and this new doctor is not willing to prescribe it to me anymore stating that the FDA has linked Acyclovir to causing cancer after 1 year of use. I can't find anything on FDA website or Google linking long term effects causing cancer. I don't know why a doctor would say this to a patient if there weren't any solid facts??

[selenadee]

I have also never heard of acyclovir causing cancer. I took it as a preventive for a year after I first got infected, but like you said, it was not very effective. My doctor changed my prescription to valacyclovir 250 mg/day x2, which finally stopped the outbreaks.

[chevy145]

I've been taking it for 25 yrs with no issues. At some point I stopped having outbreaks, but I will continue to use acyclovir.