Acyclovir vs Valacyclovir vs Famciclovir: Herpes Antivirals Compared

Acyclovir, valacyclovir, and famciclovir all block herpes from replicating. They manage outbreaks and cut transmission but don't cure HSV. They're equally effective. Valacyclovir is usually preferred because it needs fewer daily doses (often once daily for suppression versus five times daily for acyclovir). Famciclovir is a solid alternative if valacyclovir doesn't suit you.

The three drugs and how they work

All three antivirals interrupt the same step in the herpes life cycle: they're built into the viral DNA chain as the virus copies itself, which stops replication. None of them clears the virus from your body. HSV stays dormant in nerve cells between outbreaks, so these drugs shorten and prevent flares and reduce the odds of passing the virus to a partner. For the bigger picture on the infection itself, see our overview of genital herpes.

Acyclovir (the original)

Acyclovir was the first oral antiviral for herpes, FDA approved in 1982, and it still works well. Its weakness is absorption: only about 15–20% of an oral dose reaches your bloodstream, which is why it has to be taken so often, up to five times a day for an episodic course CDC, 2021. It's the cheapest of the three and has the longest track record, which matters in pregnancy.

Valacyclovir (the convenient prodrug)

Valacyclovir (brand Valtrex) is a prodrug, an inactive form your body converts into acyclovir after you swallow it. That conversion is far more efficient, giving it about 55% bioavailability versus 15–20% for plain acyclovir. The practical payoff is fewer pills: you can suppress outbreaks with a single daily dose. That convenience is why it's the most commonly prescribed of the three.

Famciclovir (the alternative prodrug)

Famciclovir (brand Famvir) is a prodrug of penciclovir, a related antiviral. Its absorption is similar to valacyclovir's, and it's just as effective. It's simply prescribed less often, partly out of habit and partly on cost. It's the go-to backup when valacyclovir causes side effects or someone wants to try something different.

Side-by-side comparison

Dosing in practice: episodic vs suppressive

There are two ways to take any of these drugs, and the choice drives everything about your regimen. Episodic therapy means a short course only when an outbreak starts, ideally at the first tingle or itch, before blisters fully form, when the drug helps most. Suppressive therapy means a daily dose taken indefinitely to prevent outbreaks and lower transmission risk. We break down how to choose between them in our guide to herpes treatment — episodic vs suppressive.

A typical episodic course runs about five days. On acyclovir that means juggling five doses a day; on valacyclovir it's twice a day or even once daily; on famciclovir it's three times daily. For suppression the contrast is starker: acyclovir is twice daily, valacyclovir can be a single pill, and famciclovir is twice daily. Over months and years, fewer daily doses means you're far less likely to miss one, and consistency keeps the virus quiet.

Daily suppression cuts outbreak frequency by roughly 70–80% and reduces asymptomatic viral shedding, the silent release of virus from the skin that drives most transmission even when you have no symptoms.

Cost and generic access

All three are available as generics in the US, so brand-name pricing rarely makes sense. Acyclovir is the cheapest, often running about $20–$40 a month for suppression. Generic valacyclovir is widely stocked and runs roughly $30–$60 a month at list price, though smart shopping pays off there.

With insurance, all three are usually covered. Without insurance, discount tools like GoodRx, Cost Plus Drugs, and patient-assistance programs can drop generic valacyclovir to under $20 a month at many pharmacies. The gap between a pharmacy's list price and the discounted price can be dramatic, so price-compare a couple of options before you fill the prescription. Famciclovir's generic exists but tends to cost more than generic valacyclovir, one reason it's prescribed less.

Which one is usually preferred — and why

Valacyclovir is the default for most people, and the reasoning is mostly practical rather than clinical. The CDC's 2021 guidelines treat all three as equivalent in efficacy for both episodic and suppressive therapy. What separates them is convenience, and valacyclovir wins on dosing: a once-daily suppressive pill versus acyclovir's twice-daily schedule, plus the five-times-daily slog of episodic acyclovir.

There's also good evidence on transmission specifically. In a randomized trial, daily valacyclovir reduced transmission of HSV-2 to uninfected partners by about 48% Corey, NEJM 2004, meaningful protection that, combined with condoms and disclosure, substantially lowers a partner's risk. A reasonable thing to say to your provider: "I'd like the easiest dosing — is generic valacyclovir right for me?"

Who might do better on famciclovir

Famciclovir earns its place as the backup. If valacyclovir causes bothersome nausea, headaches, or dizziness, or if it just doesn't seem to be controlling your outbreaks, famciclovir is a reasonable switch, and the change is simple — just ask your provider for a new prescription. Some people also tolerate one prodrug better than the other for reasons that aren't fully predictable. With an equally effective alternative on hand, there's no need to suffer through side effects on a drug.

Pregnancy and breastfeeding

All three antivirals are considered safe in pregnancy. Acyclovir has the longest safety record and is listed first by the CDC for use during pregnancy, with valacyclovir also used frequently, often near term to reduce the chance of a flare at delivery. If you're pregnant or planning to be and have herpes, have this conversation early with your obstetric provider so the plan is set well before your due date. Side effects across all three are usually mild, but anyone with kidney disease should have renal function monitored, since high doses can stress the kidneys.