For daily herpes suppression, 500 mg and 1 g of valacyclovir are not interchangeable. If you get fewer than ten outbreaks a year, 500 mg once daily controls them as well as the higher dose (Reitano 1998). At ten or more a year, 1 g once daily works better. Outbreak frequency, not preference, sets the dose.
Both doses beat placebo. The gap is in the details.
Daily suppressive therapy means one antiviral pill every day, whether or not you have symptoms, to keep genital herpes outbreaks from starting. Across the once-daily options, more drug does more work, but only up to a point that depends on you.
The clearest evidence comes from a one-year randomized trial in 1,479 people with recurrent genital herpes (Reitano 1998). It compared valacyclovir at 250 mg, 500 mg and 1 g once daily against placebo. Every dose beat placebo at preventing or delaying recurrences. There was also a dose-response across the once-daily arms, meaning higher doses prevented more outbreaks on average. The practical question is who actually needs that extra prevention.
The line that decides it: ten outbreaks a year
The same trial split patients by how often they recurred, and the split is where the dose decision lives. People with a history of fewer than ten recurrences a year were controlled just as well on 500 mg once daily as on anything higher. People with ten or more a year did better on 1 g once daily (Reitano 1998). That threshold is why 500 mg is the standard starting dose and 1 g is the step-up, not the default.
| Suppression regimen | Who it fits | What the evidence shows |
|---|---|---|
| 500 mg once daily | Fewer than 10 recurrences a year | Controls recurrences as well as higher regimens in this group (Reitano 1998); the dose Corey 2004 used to cut partner transmission by about half |
| 1 g once daily | 10 or more recurrences a year | More effective than 500 mg once daily in frequent recurrers (Reitano 1998) |
| 250 mg twice daily | 10 or more recurrences a year | As effective as 1 g once daily in frequent recurrers (Reitano 1998); two pills a day instead of one |
The transmission evidence is specifically the 500 mg dose
If your reason for daily suppression is protecting a partner, one detail matters more than the dose ladder. The landmark transmission trial gave once-daily valacyclovir 500 mg to the partner who had HSV-2, and it cut the risk of passing the virus to a susceptible partner by about 48 percent over eight months (Corey 2004). No trial has tested whether 1 g once daily lowers transmission any further. So the transmission benefit is the one documented for 500 mg. Someone who steps up to 1 g for frequent outbreaks keeps that benefit, and there is no reason to reach for 1 g on transmission grounds alone.
Twice a day is a real alternative to the higher single dose
For frequent recurrers, 250 mg twice daily worked as well as 1 g once daily in the same trial (Reitano 1998). It splits the day's dose into two smaller pills. Some people keep a morning-and-night rhythm more reliably than a single larger tablet; others would rather take one pill and forget it. Neither is more effective. The better regimen is the one you will take every day, since a suppression dose only works while you keep it up.
Kidney function changes the math
All of these doses assume normal kidney function. Valacyclovir clears through the kidneys, so reduced function calls for a lower dose or a longer interval, and that adjustment matters more as the dose climbs. This is one reason daily suppression is a prescriber decision rather than a self-managed one. A clinician sets the starting dose from your recurrence history and your kidney function, then adjusts if outbreaks stay frequent.
The bottom line
Start at 500 mg once daily if you get fewer than ten outbreaks a year. It controls recurrences as well as any higher dose in that group, and it carries the transmission evidence. Move to 1 g once daily, or to 250 mg twice daily, if you get ten or more a year, where the lower dose can fall short. The number that drives the choice is how often you recur, so it is worth counting honestly before you and a clinician settle on a dose.
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This article is for education and is not a substitute for individual medical advice from your own clinician.