Valacyclovir 500mg is an antiviral medication used to treat infections caused by certain types of herpes viruses. Its three main uses are treating genital herpes (both initial and recurring outbreaks), treating shingles (herpes zoster), and treating cold sores (oral herpes). The 500mg tablet is also widely prescribed as a daily suppressive therapy to reduce the frequency of genital herpes outbreaks and lower the risk of transmitting the virus to a sexual partner.
Conditions Treated With Valacyclovir
Valacyclovir targets three related but distinct viral infections, all caused by members of the herpes virus family:
- Genital herpes (HSV-2 and sometimes HSV-1): Used for first-time episodes, recurrent outbreaks, and ongoing daily suppression to prevent future flare-ups.
- Cold sores (oral herpes, HSV-1): Prescribed as a short, high-dose course at the first sign of tingling or blistering on or around the lips.
- Shingles (varicella-zoster virus): Used to reduce the severity and duration of the painful, blistering rash that occurs when the chickenpox virus reactivates later in life.
The 500mg strength is the most commonly dispensed tablet, though the number of tablets per dose and the length of treatment vary depending on the condition.
How Valacyclovir Works
Valacyclovir is a prodrug, meaning it doesn’t do the antiviral work itself. After you swallow it, your body rapidly converts it into acyclovir (the active drug) during absorption through the gut and liver. This conversion is essentially complete by the time the drug reaches your bloodstream, which is why valacyclovir delivers much higher blood levels of acyclovir than taking acyclovir tablets directly.
Once acyclovir reaches virus-infected cells, those cells activate it through a series of chemical steps. The first step depends on an enzyme that only the virus produces, which is why the drug concentrates its effects in infected cells and largely leaves healthy cells alone. The activated form then interferes with the virus’s ability to copy its own DNA, stopping the infection from spreading to new cells. This doesn’t eliminate the virus from your body (herpes viruses remain dormant in nerve tissue), but it shortens outbreaks, reduces symptoms, and limits how much virus you shed.
Genital Herpes: Outbreaks and Suppression
Genital herpes is the most common reason valacyclovir 500mg is prescribed. It serves three distinct purposes depending on where you are in the course of the infection.
For a first episode of genital herpes, higher doses are typically used (1,000mg twice daily for 10 days). For recurrent outbreaks, the standard approach is 500mg taken twice daily for 3 days, started as soon as you notice symptoms. Timing matters: the earlier you begin treatment, the more effectively it shortens the outbreak. In clinical trials, people who took valacyclovir 500mg stopped shedding virus in a median of 2 days, compared to 4 days with a placebo.
The third use, daily suppressive therapy, is where the 500mg dose is most distinctive. If you experience frequent outbreaks (generally nine or fewer per year), taking 500mg once daily can significantly reduce how often they occur. For people with more frequent recurrences, the dose is typically doubled. Beyond controlling your own symptoms, daily suppressive therapy reduces the risk of transmitting genital herpes to an uninfected partner. In a large clinical trial, daily valacyclovir cut the risk of a partner developing symptomatic herpes by 75% and reduced overall transmission of the virus by 48%.
Cold Sores
For cold sores, valacyclovir is used differently than for genital herpes. The standard protocol is a short, intensive one-day treatment: two grams (four 500mg tablets) taken at the first sign of a cold sore, followed by another two grams 12 hours later. That’s the entire course. The goal is to hit the virus hard and early, ideally during the tingling or itching stage before a blister fully forms. Starting treatment after blisters have already appeared still helps but is less effective at shortening healing time.
Shingles
Shingles treatment uses the highest doses of valacyclovir: 1,000mg three times daily for 7 days. While the individual tablets are 500mg, you’d take two tablets per dose. Treatment should begin as soon as possible after the rash appears, ideally within 72 hours. Starting within that window helps reduce the severity of the rash, shorten its duration, and lower the risk of postherpetic neuralgia, the lingering nerve pain that can persist for months after the rash heals. Valacyclovir doesn’t prevent shingles (the shingles vaccine does that), but it meaningfully reduces the burden of an active episode.
Side Effects
Valacyclovir is generally well tolerated. The most commonly reported side effects in clinical trials are headache, nausea, and abdominal pain. These tend to be mild and resolve on their own. Dizziness and fatigue occur less frequently.
Because the drug is cleared through the kidneys, people with reduced kidney function need adjusted doses. For most indications, no dose change is necessary if your kidney function is moderately reduced, but at lower levels of function, the frequency or amount is scaled back. Your prescriber will typically check kidney function before starting you on a long-term suppressive regimen. People on dialysis take their dose after each session. Staying well hydrated while on valacyclovir helps your kidneys process the drug efficiently.
What Valacyclovir Does Not Do
Valacyclovir does not cure herpes. The virus remains in your nerve cells in a dormant state, and outbreaks can still recur after you stop taking the medication. It also does not completely eliminate the risk of transmitting herpes to a partner, even on daily suppressive therapy. Combining suppressive therapy with barrier protection provides the strongest risk reduction.
The drug is specifically active against herpes simplex viruses (types 1 and 2) and varicella-zoster virus. It is not effective against unrelated viral infections like the flu or COVID-19, and it has no role in treating bacterial or fungal infections.