Valacyclovir: How It Works and When You Might Need It

Valacyclovir (brand name Valtrex) is an antiviral many doctors prescribe for herpes viruses — think cold sores, genital herpes, and shingles. It’s a prodrug of acyclovir, which means your body converts it into the active medicine that stops the virus from multiplying. That helps your immune system control the outbreak faster and eases symptoms.

Common uses and typical adult doses

Different infections need different schedules. Here are common adult regimens, but always follow your prescriber’s plan:

- Shingles (herpes zoster): usually 1 gram three times a day for 7 days.
- Initial genital herpes: often 1 gram twice daily for 10 days.
- Recurrent genital herpes: options include 500 mg twice daily for 3 days or a single-day 1 g twice-daily regimen if started quickly.
- Suppressive therapy (to cut recurrences): commonly 500 mg to 1 g once daily, depending on how often outbreaks occur.
- Cold sores: some short-course regimens exist (e.g., 2 g taken twice in one day) if started very early.

If you have kidney problems, your doctor will lower the dose — valacyclovir clears through the kidneys, so hydration and dose adjustment matter.

Side effects, interactions, and practical safety tips

Most people tolerate valacyclovir well. The usual side effects are headache, nausea, stomach pain, and tiredness. Rare but serious issues include kidney problems and confusion or hallucinations, especially in older adults or people with reduced kidney function.

Keep these points in mind:

- Drink enough water while taking it to protect your kidneys.
- Tell your prescriber about other medicines, especially probenecid or drugs that affect kidney function — they can change valacyclovir levels.
- If you feel confused, very sleepy, or develop blood in the urine, stop the drug and get medical help.
- Start treatment as soon as symptoms begin. Antivirals work best when started early in an outbreak.
- For genital herpes, avoid sexual contact during lesions and until a clinician says it’s safe.

Pregnancy and breastfeeding: doctors sometimes use valacyclovir during pregnancy for severe or frequent outbreaks, but you should discuss risks and benefits with your provider.

Missed dose? Take it as soon as you remember unless the next dose is near; then skip the missed dose. Don’t double up.

Questions for your prescriber: Are there safer dose adjustments for my kidney function? How long should I stay on suppressive therapy? When can I safely resume sexual activity? These are practical, important questions — ask them.

Valacyclovir is a common, effective antiviral when used correctly. It won’t cure herpes, but it reduces symptoms, shortens outbreaks, and can cut down how often they happen. If you’re unsure about dosing or side effects, talk to your healthcare provider — and keep hydrated while on treatment.