Yes, you can still get herpes from a partner who takes daily antiviral medication, but the risk is significantly lower. In the largest clinical trial on this question, published in the New England Journal of Medicine, daily antiviral therapy cut the rate of transmission to an uninfected partner by about half overall and reduced the risk of symptomatic infection by 75%.
Medication is one of the most effective tools available for reducing transmission, but it doesn’t eliminate the possibility entirely. Understanding exactly how much protection it offers, and what else you can do to lower your risk, helps you make informed decisions.
How Much Medication Reduces the Risk
The key numbers come from a study of over 1,400 couples where one partner had genital herpes (HSV-2) and the other did not. The infected partner either took a daily antiviral or a placebo for eight months. Among partners of people on placebo, 3.6% picked up the virus. Among partners of people on the antiviral, that dropped to 1.9%.
When researchers looked only at cases where the newly infected partner actually developed symptoms (sores, pain, flu-like illness), the difference was even more striking. Symptomatic herpes appeared in 2.2% of the placebo group’s partners versus just 0.5% of the antiviral group’s partners. That’s a 75% reduction in the chance of developing noticeable herpes.
Put another way: if your partner takes daily medication, your risk over an eight-month period is roughly 1 in 50 for picking up the virus at all, and about 1 in 200 for developing a symptomatic infection. Those aren’t zero, but they’re considerably lower than without medication.
Why the Risk Isn’t Zero
Herpes spreads through skin-to-skin contact, and the virus can be present on the skin even when there are no visible sores. This is called asymptomatic shedding, and it’s actually responsible for a large share of transmission. A person with HSV-2 who isn’t on medication sheds the virus on about 5% of days without symptoms. Daily antivirals reduce that to about 1.5% of days, a 71% drop. But on those remaining days, the virus is still present and can still be passed along.
In studies, 84% of people taking daily antivirals had no detectable viral shedding at all during the study period, compared to 54% on placebo. That means roughly 1 in 6 people on medication still shed the virus at some point. The medication suppresses viral activity dramatically, but the herpes virus lives in nerve cells and periodically reactivates in ways that even consistent medication can’t always block.
How Quickly Medication Starts Working
Daily antiviral therapy doesn’t provide full protection from day one. Research published in the Journal of Infectious Diseases found that it takes about five days of consistent daily use before the medication fully suppresses viral shedding. If your partner just started their prescription or has been taking it inconsistently, the protective effect may not yet be at its peak. Consistent, uninterrupted daily use is what the transmission studies were based on.
During an Active Outbreak
The transmission numbers above reflect the overall risk across months of regular sexual activity, including periods without symptoms. During an active outbreak, when sores are visible, the risk of transmission is highest regardless of whether someone is on medication. Most guidance for couples in this situation is straightforward: avoid direct contact with the affected area while sores are present and healing. Medication reduces how often outbreaks happen and how long they last, which indirectly lowers your exposure to these high-risk windows.
Layering Protection Methods
Medication works best as part of a broader approach rather than the only line of defense. Condoms provide an additional barrier, and studies have shown they independently reduce herpes transmission risk. The landmark valacyclovir trial encouraged condom use among all participants, meaning the real-world numbers already reflect some degree of combined protection. Using both daily antivirals and condoms consistently gives you the lowest overall risk, though no combination eliminates it completely.
Avoiding sexual contact during active outbreaks adds another layer. Even small signs like tingling, itching, or skin sensitivity in the area (sometimes called prodromal symptoms) can signal that the virus is active before sores appear. Many people with herpes learn to recognize these early warning signs over time.
What the Data Doesn’t Cover
Almost all of the transmission research focuses on HSV-2, the strain traditionally associated with genital herpes. HSV-1, which causes the majority of new genital herpes cases in younger adults (often transmitted from oral cold sores), has not been studied in the same way. The CDC notes that no data exist on whether suppressive antiviral therapy prevents HSV-1 genital transmission. The medication likely reduces HSV-1 shedding to some degree, since it works against the same viral family, but the specific risk reduction for partners hasn’t been measured.
The major clinical trial also studied heterosexual couples specifically. Data on transmission rates in same-sex couples on suppressive therapy are limited, though the biological mechanisms of shedding and suppression are the same regardless of the type of sexual contact involved.
Putting the Risk in Perspective
For many couples where one partner has herpes, the practical risk is lower than they expect. Without any precautions at all, the annual transmission rate for HSV-2 in discordant heterosexual couples is estimated at around 5 to 10%, varying by the direction of transmission (male-to-female transmission is more common than female-to-male). Daily antivirals cut that roughly in half. Add consistent condom use and outbreak avoidance, and the annual risk drops further, likely into the low single digits.
The bottom line: medication substantially reduces but does not eliminate transmission risk. Your partner’s daily antiviral use is one of the most meaningful steps they can take to protect you, and combining it with other precautions brings the risk down even further.