Valacyclovir: How It Works, Side Effects & More

Having safe sex to prevent sexually transmitted infections (STIs) may seem like a no-brainer. But we also understand the very real stigma that comes with an STI like herpes.

Herpes is caused by two viruses: the herpes simplex virus type 1 (HSV-1) and the herpes simplex virus type 2 (HSV-2). It was initially thought that oral cold sores were only due to HSV-1 and that genital herpes was only caused by HSV-2; however, either virus can cause outbreaks at either location. According to the World Health Organization, 64 percent of people under age 50 globally have HSV-1, and 13 percent of the global population between ages 15and 49 have HSV-2. and 

The bad news is that there’s no cure for herpes. The good news is that consistent treatment can manage the severity of herpes outbreaks.

Plus, various treatment options are available, including Valtrex^® — or valacyclovir, the generic version — an antiviral medication.

So, what is valacyclovir? Can this medication be used to stop a cold sore? Are there adverse effects, and if so, how long do Valtrex side effects last?

Dealing with herpes and starting a new medication can be overwhelming. We’re here to answer the above questions and go over other key information about valacyclovir.

Is valacyclovir an antibiotic or another type of medication? And is there a difference between Valtrex — the brand-name medication, and valacyclovir — the generic medication?

Valacyclovir is an antiviral drug designed to manage HSV (herpes simplex virus), shingles (herpes zoster), and VZV (varicella-zoster virus, more commonly known as chickenpox) infections.

As mentioned above, valacyclovir is Valtrex’s generic name. But you don’t have to worry about generic versus brand-name medication. Generic drugs are required by the FDA (U.S. Food and Drug Administration) to be the same dosage, safety, effectiveness, strength, and quality as their brand-name counterparts.

Valacyclovir is an extremely well-studied medication prescribed to people of all ages. It’s been widely and successfully used to control and treat the symptoms of HSV-1 and HSV-2.

Now that you know what this medication is, you might be wondering: How does valtrex work?

We mentioned that valacyclovir is an antiviral drug, meaning the medication fights infections caused by viruses. However, valacyclovir isn’t classified as an antibiotic. 

(Antibiotics are medications that help the immune system fight infections caused by bacteria, not viruses.)

Like many medications, valacyclovir works through a complex chemical process that interferes with how the herpes virus reproduces. This makes it easier for the body to control the infection. Valacyclovir itself is a prodrug (meaning it converts into another substance in the body). It converts into acyclovir (another antiviral herpes medication) after it passes through the liver.

Comparing valacyclovir versus acyclovir, valacyclovir has a far higher level of bioavailability. This means more of the drug will make it into your body..

Valacyclovir helps sores that developed from the virus heal faster while making the aches, cold symptoms, and other signs of herpes less severe.

Oh, and if you’re curious about having sex with herpes, you’ll be glad to know valacyclovir can lower the transmission rate of the virus — meaning it reduces its ability to spread.

In one study, researchers found that people with HSV-2 using valacyclovir were almost 50 percent less likely to transfer the virus to their sexual partners than those with HSV-2 who didn’t use medication.

But know that valacyclovir isn’t a 100 percent effective solution for preventing herpes. Herpes infections are contagious, and you can infect other people even while taking the medication.

How fast valacyclovir works depends on several factors, from the type of infection to how quickly you start treatment after noticing symptoms. But on average, most people see a resolution of symptoms between four and nine days if started early enough.

Valacyclovir dosages also vary. Several dosage forms are available, each based on the type of HSV or VZV virus being treated and the patient’s age.

Dosages include:

• A 1,000-milligram dose of valacyclovir, given three times daily for seven days, is typically prescribed for shingles. Treatment should begin within 72 hours of noticing shingles.

• For adults with cold sores, a 2,000-milligram dose of valacyclovir is taken every  12 hours for one day.

• If treating a first outbreak of genital herpes, adults take 1,000 milligrams of valacyclovir two times daily for 10 days, beginning treatment within 48 hours of the first sign of herpes symptoms.

• Adults with recurring genital herpes are usually prescribed 500 milligrams of valacyclovir two times daily for three days. It’s recommended to begin valacyclovir treatment as soon as a recurrent herpes symptom becomes visible.

While these are typical dosages, your prescription will be as unique as you and tailored to your symptoms, age, and general health.

If you miss a dose, take it as soon as you remember. If it’s almost time for your next dose, skip the missed dose — don’t double the dose to catch up.

The best treatment plan for herpes? Seek medical advice from a healthcare provider and follow their recommendations.

It’s especially crucial to talk to a healthcare provider if you have kidney problems or a weakened immune system, as these medical conditions can affect the safety of valacyclovir treatment.

Breastfeeding or pregnant women should also discuss the risks of valacyclovir treatment with their healthcare provider, as the medication can pass into breast milk.

Like any medication, there are possible side effects of valacyclovir. The most common valacyclovir side effects are usually vomiting, diarrhea, headache and nausea. Side effects, if you experience any, usually show up within hours to days of starting treatment. 

There’s also a chance of experiencing less common side effects of valacyclovir:

• Dizziness

• Confusion

• Rash

• Renal impairment

• Abdominal pain

• Agitation

Even more uncommon side effects include:

• Leukopenia (low white blood cell count)

• Neutropenia (low levels of a certain white blood cell)

• Severe allergic reaction

Get in touch with your provider if you experience any of these adverse effects.

Valacyclovir Interactions

Valacyclovir is known to potentially interact with other antiviral and immunosuppressant drugs, particularly those used in HIV/AIDS management.

Medications that might interact with valacyclovir include foscarnet, tenofovir, mycophenolate, and zidovudine, as well as the varicella virus and zoster virus vaccines.

Again, the best way forward is to talk to a healthcare professional about potential drug interactions if you use any prescription drugs or over-the-counter supplements — before you take valacyclovir or any other herpes treatment.

Who Should Avoid Using Valacyclovir? 

While it’s effective and is generally considered to be a safe option for most people, this medication may not be the best choice for everyone. Your provider may recommend something else if you: 

• Have a known allergy to valacyclovir or acyclovir 

• Currently taking any other medications that may be damaging to your kidneys

• Have a history of kidney disease, diabetes, or hypertension (high blood pressure)

• Are of advanced age

As with any new medication, if you’ve been prescribed valacyclovir, it’s normal to have questions. 

It’s always best to discuss these with your healthcare provider or pharmacist, but here are some tips to help you achieve the best outcomes when using valacyclovir: 

• When you have a prescription, start taking valacyclovir at the first sign of infection and use only as directed. Ideally, it should be started within 24 hours.  

• Stay hydrated (always, but especially when on this medication) to help prevent rare but potentially serious kidney complications. 

• Continue taking valacyclovir for as long as you’ve been directed to, even if the signs of your infection have cleared. Stopping it too early can make it more likely for your infection to return and be harder to treat. 

• You can take this medication with or without food, but taking it with food may help alleviate nausea. 

• It’s important to continue wearing a condom during sexual contact, even if you or your partner are on valacyclovir, to minimize the risk of transmission. 

• While this drug is used to treat certain viral infections, that does not mean it should be used (or is effective for) treating things like the common cold.

Herpes and cold sores are an unfortunate possibility if you’re sexually active. But there are ways to manage symptoms. Valacyclovir is among the leading options for the treatment of herpes.

• What is valacyclovir? It’s an antiviral drug used to treat herpes simplex virus (HSV) and varicella-zoster virus (VZV, more commonly known as chickenpox) infections. One common brand name for valacyclovir is Valtrex^®.

• What does valtrex do? The drug slows down the growth of herpes, making it easier for the body to control the infection, and reduces symptoms. Although there isn’t a cure for herpes, valacyclovir can help manage symptoms like body aches and sores.

• What are the side effects? There’s a possibility of experiencing mild side effects, most commonly vomiting, diarrhea, headache, or nausea. Valacyclovir can also interact with other medications, including other antiviral and immunosuppressant drugs.

If you’re dealing with herpes (or think you might have the virus) and are interested in valacyclovir as a treatment, talk to your healthcare provider about your symptoms. They can come up with a treatment plan for your unique needs.

You can also connect with a healthcare professional to learn about what sexual health treatments are available.