Acyclovir is an antiviral drug, often used to treat the herpes simplex virus that causes cold sores. While the virus itself can never be fully cured, drugs like acyclovir can help to control cold sore outbreaks and lessen the symptoms.

It is often sold under the brand name Zovirax. In some cases, you can take acyclovir as an oral medication. However, Zovirax is a topical cream that you can apply directly to a fever blister to promote faster healing.

With so many different cold sore treatments on the market, it’s important to know which one is right for you, and why it will work the best. You may ask yourself how does acyclovir work in the body, or how long it will take to notice results from regular use?

This article will cover the ins and outs of what you can expect when you use Zovirax as recommended. If you’re prone to outbreaks from HSV-1, finding a solution that provides consistent relief is important. Is Zovirax the right solution?

How Does Acyclovir Work?

As an antiviral agent, acyclovir prevents viruses within the body from multiplying. When a virus like herpes simplex becomes too strong, it can cause a cold sore flare up. The drug will also reduce the severity of the outbreak and can speed up the healing time. It works especially well on those who have a weakened immune system, which is known to cause outbreaks in the first place.

If your cold sore blisters cause itching and burning, this topical cream can also help to reduce the pain. Often, that can be the worst part about a fever blister, so finding relief in an easy-to-use treatment alone can make the entire thing worth it.

When using acyclovir as an oral medication, it is best to have a constant stream in your system at all times. Your doctor should be able to give you a schedule when it comes to how often you should take the drug for it to be most effective.

For topical applications, like Zovirax, you should still apply it regularly throughout the day to let the medication work fully, around the clock.

Acyclovir can’t kill the herpes simplex virus, but it can make its effects much weaker within the body. If you’re someone who gets cold sores frequently, reducing their healing time, severity, and frequency can be the most important way to get treatment. Acyclovir does all of that and helps to weaken symptoms at the same time.

How Long Does Zovirax Take to Work?

Whether you’re using the oral medication or a topical form of acyclovir like Zovirax, it’s always best to use it at the first sign of a cold sore. If you’ve experienced blisters before, you’ll know your early symptoms better than anyone. They often include things like tingling around the mouth. The earlier you’re able to start treatment, the better it will work.

The typical lifespan of a cold sore can be different for everyone. However, in some cases they can last weeks, going through different stages. Acyclovir is designed to significantly speed up the healing process, no matter what stage of the cold sore you’re experiencing.

If you’re using Zovirax, cover the affected area completely. It is recommended that you use the treatment five times a day, every four hours, for best results. It’s also best to use it around the same times each day, for consistency. If you follow these instructions, you should notice that your cold sore healing in just four days. The cream contains an ingredient called MAC-P, which allows it to be absorbed into the skin faster, to speed up the healing time of the blister.

If acyclovir has been prescribed to you by a doctor, continue using it until it is completely gone. Even if the cold sore has disappeared and the symptoms are gone, never stop using the treatment early, or its return. You may also be putting yourself at risk for another flare up. The point of the medication is to weaken the herpes simplex virus. That can only be completed if the medication is used to its fullest.

Does Zovirax Have Any Side Effects?

As with any medication that doesn’t use completely natural ingredients, there are potential side effects to consider. The most common side effects associated with the oral use of acyclovir include:

  • Nausea
  • Diarrhea
  • Headache
  • Vomiting

Reactions to topical creams containing acyclovir are usually less severe if they occur. It isn’t common for most people to experience an allergic reaction to a medication like Zovirax. However, potential side effects include itching and burning at the site of application. If you notice other allergy-related symptoms, such as a rash, itching or swelling, or trouble breathing, contact your doctor immediately.

Additionally, there are several precautions you should take before using this medication in any form. If you’re pregnant, it should only be used when desperately needed. If you’re taking the medication orally, it could also be transferred into breast milk. Discuss risk factors during pregnancy and breastfeeding with your doctor. Cold sores aren’t transferred through breast milk.

Other anti-inflammatory drugs, especially prescription drugs, may interact negatively with acyclovir. You should also avoid drinking alcohol while using the medication. Drinking will increase the concentration of the medication within your body. Any negative side effects may increase in severity with the consumption of alcohol. It also may cause dizziness or fainting.

Acyclovir may be taken by children as an antiviral medication. However, it’s best to contact their pediatrician before giving it to them orally. Using a topical solution like Zovirax may prove to have less potential side effects for young children.

If you’re looking for an alternative, we recommend two treatments. If you want an FDA-approved cream, you can get good results with HERP-B-GONE. Should you want to utilize the latest technology and shorten the healing time to just 3 days, give the Virulite Cold Sore Device a try.

Is it Practical?

If you choose to use Zovirax to heal your fever blisters, it is a practical solution. Far too often, cold sore creams and ointments come in bottles or tubes that can create messes. More of the medication ends up oozing out of the bottle or spreading too thin on the sore than penetrating the skin.

Zovirax comes in an easy-to-use bottle with a pump. You can get the amount you need and apply it to the blister. Its fast-acting formula will penetrate the skin quickly, so you don’t have to worry about it smearing off before it gets a chance to work through your system.

The size of the bottle makes it convenient to use, too. Outbreaks can occur at any time. If you’re prone to them, it’s important to have a treatment option on hand wherever you go. This bottle can fit in your purse, suitcase, etc., so you’re always prepared. It’s one of the easiest-to-use cold sore remedies on the market today, thanks to a few small design touches, and it’s fast-acting formula.

What are the Advantages & Disadvantages?

There are dozens of over the counter and prescription cold sore treatment options on the market. Some are oral, some are topical, just like the options here.  What makes acyclovir the best for current and future outbreaks? For this pros and cons list, we’ll focus on Zovirax as a topical solution, and what you can expect from regular use when you’re treating an embarrassing blister.


  • The cream comes in an easy-dispensing pump to reduce mess.
  • It is clinically proven to speed up the healing time of cold sores.
  • Acyclovir is the key active ingredient, so you’re getting the benefits of its antiviral properties without having to take oral medication.
  • You can use it at any stage of a cold sore.
  • If you use it a the beginning stages, it can greatly decrease blister symptoms.
  • The tube is small and portable.

How to use Acyclovir cream for cold sores


  • Some people may have negative skin reactions.
  • It does require consistent use, every four hours.

The biggest drawback in using Zovirax is that you have to apply it consistently, every few hours. This might not be a problem for some people, but to others, it can be seen as an inconvenience. If you’re desperate to get rid of your cold sore, this treatment can get results much faster. Plus, it only takes four days of treatment to be effective. That’s far less than other treatment options that may require a week or more of daily use.

Is Acyclovir the Best Cold Sore Treatment Option?

What makes acyclovir so great is that it works on outbreaks from the inside out. Even Zovirax, as a topical solution, is designed to help weaken the herpes simplex virus. It minimizes the healing time and reduces cold sore symptoms in the process. But, it focuses more on the actual virus than the flare ups that occur from it.

Because it does attack the virus, you can expect fewer flare-ups overall. When you do experience one, it should also be less severe, and not last as long. Acyclovir can work for anyone, even if you rarely get fever blisters. However, if you know you’re more prone to them, keeping the medication on you at all times can make a big difference in how quickly your cold sores start to heal.

If you’d like to find out more about our top pick, we recommend finding out more about the Virulite cold sore machine.