Acyclovir: What It Is, How It Works, and What Alternatives Exist

When you get a cold sore or a flare-up of genital herpes, acyclovir, a synthetic antiviral drug that stops herpes viruses from multiplying. Also known as Zovirax, it’s one of the most prescribed antivirals for herpes simplex and varicella-zoster infections. It doesn’t cure the virus—no drug does—but it cuts down the pain, speeds up healing, and lowers how often outbreaks happen. If you’ve ever used a cream or taken a pill during a breakout, chances are it was acyclovir.

Acyclovir works by slipping into the virus’s DNA-making machine and jamming it. The virus tries to copy itself, but acyclovir tricks it into using a broken blueprint. That stops the infection from spreading. It’s most effective when taken early—right when you feel that tingling before the blister shows up. For some people, daily low doses prevent outbreaks altogether. It’s used for oral herpes (cold sores), genital herpes, shingles, and even chickenpox in kids or adults with weak immune systems.

But acyclovir isn’t the only option. valacyclovir, a prodrug that turns into acyclovir in the body is popular because you take it less often—once or twice a day instead of five. Then there’s famciclovir, another antiviral that works similarly but has a faster onset. Both are more expensive, but if you’re traveling or hate swallowing pills five times a day, they’re worth considering. Topical creams like acyclovir ointment help with cold sores, but they don’t work as well as pills for serious outbreaks. And if you’re allergic or resistant? Doctors might turn to topical docosanol or even newer drugs like pritelivir, though those are still rare.

People often ask if acyclovir helps with other viruses—like the flu or COVID. It doesn’t. It’s laser-focused on herpes family viruses. That’s why it’s not a cure-all, but it’s incredibly reliable for its specific job. If you’ve had recurrent outbreaks, you’ve probably learned what triggers yours—stress, sun, illness—and pairing that with acyclovir can cut your flare-ups in half. Some users report side effects like nausea or headaches, but most tolerate it fine. Long-term use is safe for many, which is why it’s a go-to for people with frequent herpes.

What you’ll find below are real comparisons and practical guides. We’ve got posts on how acyclovir stacks up against other antivirals, what to do if it stops working, and how to manage outbreaks without relying solely on pills. You’ll also see how it fits into broader treatment plans—for people with HIV, organ transplants, or chronic skin conditions. No fluff. No marketing. Just what works, what doesn’t, and what you actually need to know.