Is There Pre-exposure Prophylaxis for Herpes?

Hepesvirus capsid protein
Herpesvirus capsid protein. Laguna Design/Science Photo Library/Getty Images

Fact or Myth?  "If I take Valtrex 24 hours before having sex with someone, I can't get herpes"

Someone once told me that they'd "heard from a friend" that if they took herpes medication the day  before having sex with someone who was infected with genital herpes, they wouldn't be at risk of becoming infected themselves. They wanted to know whether it was true and, if so, how they could go about getting a prescription.

My response was that, as far as I knew, there had been no research on whether acyclovir could be used as pre-exposure prophylaxis (PrEP) to prevent a herpes infection. Having now looked into it, that appears to be the case. (I have no idea why no one has done the research. It seems like something that a lot of people would be interested in. Someone should get on that.)

Interestingly, what has been looked at is the impact that pre-exposure prophylaxis for HIV has on genital herpes transmission. Why? Because genital herpes infections increase a person's risk of acquiring HIV. Therefore, scientists have an interest in preventing genital herpes in populations who are at high risk of exposure to HIV. As such, it's been beneficial for them to investigate how much bang they're getting for their buck when oral tenofovir is used as PreP.

Unfortunately, the answer remains unclear. There isn't yet a lot of data on the subject, and results have been mixed.

Several studies that examined the use of tenofovir as PrEP in heterosexual individuals at risk for HIV found that the drug not only reduced the risk of HIV, it also reduced the risk of acquiring genital herpes. The reduction in herpes risk wasn't as profound as it is for HIV, as some people still got infected, but low levels of protection were there.

On the other hand, at least one study looking at the same question in men who have sex with men found no protection from herpes at all.

What's the take home message? There are probably circumstances in which HIV PrEP might help people reduce their risk of both HIV and herpes, but what those circumstances are remains unclear. As for the myth that acyclovir/valcyclovir can be used as PrEP, there is no data to either support or refute it. It might be true, it might not. Right now, there's no way to tell.

With that in mind, people's best bet for reducing the risk of herpes infection during sexual intercourse remains a combination of avoiding sex during outbreaks, consistently using condoms, and seeing if suppressive therapy may be a sensible option for a partner known to be infected with the virus. Pre-exposure prophylaxis isn't a practical option unless someone is also at high risk for HIV.

Fact or Myth Verdict: Unclear


Celum C, Morrow RA, Donnell D, Hong T, Hendrix CW, Thomas KK, Fife KH, Nakku-Joloba E, Mujugira A, Baeten JM; Partners PrEP Study Team. Daily oral tenofovir and emtricitabine-tenofovir preexposure prophylaxis reduces herpes simplex virus type 2 acquisition among heterosexual HIV-1-uninfected men and women: a subgroup analysis of a randomized trial. Ann Intern Med. 2014 Jul
1;161(1):11-9. doi: 10.7326/M13-2471.

Marcus JL, Glidden DV, McMahan V, Lama JR, Mayer KH, Liu AY, Montoya-Herrera O, Casapia M, Hoagland B, Grant RM. Daily oral emtricitabine/tenofovir preexposure prophylaxis and herpes simplex virus type 2 among men who have sex with men. PLoS One. 2014 Mar 17;9(3):e91513. doi: 10.1371/journal.pone.0091513.

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