Does Valacyclovir stop the spread of genital herpes?

Valacyclovir greatly reduces herpes transmission risk but not 100%

What’s genital herpes and who’s at risk?

There are two types of herpes (herpes simplex virus): HSV-1 and HSV-2. Oral herpes around the mouth and on the lips usually is caused by HSV-1, but not exclusively so. Around 70-80% of the population have HSV-1 inside their bodies, but only about one third of those people will ever experience an oral herpes outbreak.

HSV-2, on the other hand, most often is associated with genital herpes. That said, in recent years there’s been an increase in HSV-1 induced genital herpes, apparently spread through oral sex by partner who have HSV-1 oral herpes. The scientific consensus holds that around 15% of U.S. adults have genital herpes, but within these 15% only about 10-20% of carriers will experience a genital herpes outbreak (small, itching red bumps or white blister around your genitalia). So, most people with genital herpes aren’t even aware that they have it.

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Whether one experiences a herpes outbreak in large part depends on one’s autoimmune system. The stronger that is, the less the likelihood of an outbreak, and vice versa. Sickness or certain drugs, like chemotherapy, can temporarily weaken the immune system and give the herpes virus the opportunity for an outbreak. 

Whether you can get herpes in the first place depends on your sex life and partner. If you are concerned, it’s recommended to avoid sexual intercourse or oral sex with people who have more than seven visible outbreaks every year. There’s an increased risk that these people also have frequent “quiet” outbreaks with no or only mild symptoms, where they still are contagious but wouldn’t notice. Studies show that, statistically speaking, having sex with such a herpes carrier makes it about 30% likely that the virus will be passed on to you. Of course, if you have sex during an ongoing outbreak the risk of contagion is much higher. For other carriers, who don’t have outbreaks or other symptoms, there’s still a 10% risk that they can pass it on to other people.   


Can Valacyclovir stop genital herpes from spreading?

Valacyclovir (also known by the trade name Valtrex) is an oft-prescribed treatment for both oral and genital herpes. It also treats chickenpox, since that’s also a herpes virus strain. While valacyclovir primarily is used to prevent herpes outbreaks or lower their frequency in people who already carry the virus, by doing so the drug also lowers the risk of transmission. The weakened virus will have a more difficult time spreading to other people.

Research has found that using valacyclovir will reduce the risk of transmission by about 50%. If in addition, you use condoms, the risk of contagion drops by another 50%. So, the total risk reduction is about 75% of whatever the initial risk was. It’s not 100% safe, but a significant improvement of your odds. Keep in mind that valacyclovir can only do its magic as long as you take the drug. Studies have found that daily valacyclovir therapy for the duration of one year didn’t cause any safety issues or major side effects. Talk to your doctor about whether valacyclovir could be the right choice for you if you suffer from recurring genital herpes outbreaks. 

If you aren’t a herpes carrier yourself but your partner is, to be safer yet, just avoid having sex when your partner has an active outbreak, even if he does take valacyclovir. By the way, the same goes for oral sex. If your partner has cold sores (which are an oral herpes outbreak), don’t let him or her give you oral sex, and avoid skin-to-skin contact with the affected area on his or her mouth. 

If you know that you have genital herpes (you either had an outbreak in the past or were positively tested for it), you need to take extra care in order to prevent the virus spreading to your partner(s). Be frank about and tell your partner, practice safer sex, and avoid sex at all when you notice signs of an outbreak, however mild the symptoms.  


  1. Wald, Anna, et al. “The Relationship between Condom Use and Herpes Simplex Virus Acquisition.” Annals of Internal Medicine, vol. 143, no. 10, 2005, pp. 707–13,, 10.7326/0003-4819-143-10-200511150-00007. Accessed 30 Jan. 2020.
  2. Mujugira, Andrew, et al. “Daily Acyclovir to Decrease Herpes Simplex Virus Type 2 (HSV-2) Transmission from HSV-2/HIV-1 Coinfected Persons: A Randomized Controlled Trial.” The Journal of Infectious Diseases, vol. 208, no. 9, 30 July 2013, pp. 1366–1374,, 10.1093/infdis/jit333. Accessed 30 Jan. 2020.
  3. Pincock, Stephen. “Herpes Increases Because Oral Sex Thought Safe.” BMJ?: British Medical Journal, vol. 333, no. 7567, 2006, p. 516, Accessed 30 Jan. 2020.

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