How long does it take valacyclovir to work?

In this article:

• How long does valacyclovir take to work? 
• What can affect how long it takes valacyclovir to work?
• What is the standard valacyclovir dosage?
• Who should avoid taking valacyclovir?
• The bottom line

In this article

• How long does valacyclovir take to work? 
• What can affect how long it takes valacyclovir to work?
• What is the standard valacyclovir dosage?
• Who should avoid taking valacyclovir?
• The bottom line

Valacyclovir, sold under the brand name Valtrex, is an antiviral drug. It’s an L-valine ester of acyclovir and belongs to a class of drugs called purine nucleoside analogs. The U.S. Food and Drug Administration (FDA) has approved it to treat and prevent herpes simplex virus (genital and cold sores) and varicella-zoster virus, which can cause chickenpox and shingles.

People who take valacyclovir to treat these viruses often want to know: How long does it take for valacyclovir to work? Thankfully, valacyclovir works fairly quickly once you take it. “Valacyclovir typically begins to take effect within 2-3 days, sometimes sooner, after the first dose,” says Soma Mandal, MD, an internist at Summit Health.

Here, we’ll discuss everything you need to know about the length of time it takes valacyclovir to work, including factors that affect this time, proper dosing, and whether there are certain situations where you should not take it.

How long does valacyclovir take to work? 

If you are dealing with an outbreak of herpes, chickenpox, or shingles, you want relief as soon as possible. The good news is that valacyclovir provides fairly quick relief from symptoms.

So, how fast does valacyclovir work, exactly? “Within one to two hours of taking the first dose, valacyclovir is already working to shorten the course of your infection,” says Jacob Siegel, MD, assistant professor in Dermatology at Yale School of Medicine. “While you will not feel it working, you will know it helps when you start to notice lesions crusting over and healing more quickly.”

Raman Madan, MD, chief of dermatology at Glen Cove Hospital, concurs. While valacyclovir is absorbed quickly and starts to work within hours of taking it, you may not notice results for a few days, he says, noting that the sooner you take your first dose, the more effectively it will work. “It is best used within 72 hours of symptom onset,” he says.

How might you know that the medication has started to work? “You can tell it’s working if you notice less pain, itching, and fewer sores,” says Raj Dasgupta, MD, a quadruple board-certified physician specializing in internal medicine, pulmonology, critical care and sleep medicine and reviewer at the National Council on Aging. “The medication has fully kicked in when your symptoms are mostly gone, which typically happens within a few days, but it might take longer for some people.”

Most people can tell valacyclovir is starting to work when they observe a reduction in the severity and duration of their symptoms, Dr. Mandel says. “For example, in the case of HSV, there should be less pain, itching, and a reduction in the number of skin lesions,” she describes. “With shingles, people often notice a decrease in the intensity of pain and the size of the rash.” Full resolution of your symptoms as well as full healing of any rashes or skin lesions, indicates the full effectiveness of valacyclovir, Dr. Mandel adds.

What can affect how long it takes valacyclovir to work?

Dr. Madan says valacyclovir is absorbed by the body quickly. “It reaches peak concentration in your body 1.5-2.5 hours after taking it.” In fact, valacyclovir has three to fivefold greater bioavailability than acyclovir, another antiviral used in the treatment of herpes, chickenpox, and shingles.

For best results, you should take valacyclovir as soon as possible, after you start to show symptoms. “A very important factor in how well valacyclovir works is the timing of your first dose,” Dr. Siegel notes. “It should typically be taken within 72 hours of the onset of the flare and ideally at the very first sign of symptoms (sometimes tingling, itching, or pain).” Dr. Siegel says that valacyclovir can be taken with or without food, but you should make sure you stay properly hydrated while taking it.

According to Dr. Mandal, factors that can affect the absorption of valacyclovir include:

• Whether or not you are taking the medication as prescribed
• How strong your immune system is; people with weakened immune systems may require a different dose compared to those with normal immune systems
• Your kidney function; conditions of the kidneys can impact how valacyclovir is metabolized and excreted
• Any conditions that affect the gastrointestinal system, as these can impair absorption

What is the standard valacyclovir dosage?

 Valacyclovir, sold generically or under the brand name Valtrex, is available in capsules of 500 mg or 1000 mg. The recommended dose for adults varies, but it can be as low as 500 mg once daily or as high as 1000 mg three times daily. 

How the medication is prescribed depends in part on what condition you are treating. For example, for shingles treatment, valacyclovir is usually taken three times daily for a week. For genital herpes treatment, valacyclovir is usually taken two times a day for three to ten days, depending on if it’s your first breakout or a recurrent one.

As per DailyMed at the National Institutes of Health (NIH), adult dosing for valacyclovir is as follows:

• Herpes cold sores: Take 2000 mg two times a day for one day, 12 hours apart
• Genital herpes initial episode: Take 1000 mg two times a day for 10 days
• Genital herpes recurrence: 500 mg two times a day for three days
• Herpes zoster (shingles): 1000 mg three times daily for seven days

For chickenpox, the recommended dose for kids ages two to 18 is 20 mg per kg of weight, three times a day for five days. Children shouldn’t take more than 1000 mg of valacyclovir three times a day.

Who should avoid taking valacyclovir?

 Valacyclovir is well tolerated by most people. “In general, valacyclovir is considered to be a safe medication,” says Dr. Mandal. However, your dose may have to be adjusted if you have certain medical conditions, like kidney impairment. Also, “If you have a known allergy to valacyclovir or acyclovir, then you should not take this medication,” she warns.

Dr. Siegel agrees that valacyclovir is typically quite safe and with tolerable side effects. Still, he advises people to speak to their healthcare provider about any factors on their health that may put them at risk of serious side effects. According to Dr. Siegel, some of these risk factors include:

• Taking higher doses of the medication
• Older age
• History of kidney disease
• Hypertension (high blood pressure)
• Diabetes
• Concurrent use of any medications that may damage your kidneys

“Valacyclovir has few generally mild interactions with other medications, and taking valacyclovir rarely requires holding another medication,” Dr. Siegel points out. “However, it may diminish the effectiveness of some vaccines such as the varicella (chicken pox) or some forms of the zoster (shingles) vaccine.” Your physician may recommend that you wait to get vaccinated until at least 24 hours after you finish valacyclovir treatment. If you were just vaccinated, they may recommend that you wait 14 days after you have taken either of these vaccines to start valacyclovir.

Dr. Dasgupta says that valacyclovir can impact your kidneys. His recommendation is to stay well-hydrated and consider drinking extra fluids so you will pass more urine while you are taking valacyclovir. Doing so will “keep your kidneys working well and help prevent kidney problems,” Dr. Dasgupta explains.

Pregnant and breastfeeding women should avoid valacyclovir, says Dr. Madan. You should avoid taking it with any medications that can be excreted to the kidneys, such as NSAIDs, Dr. Madan adds.

The bottom line

Valacyclovir is well-absorbed and starts to work almost immediately after you take it. However, you won’t notice results—such as reduced pain, less itching, and fewer rashes and sores—until about two or three days later. Valacyclovir works best if you take it as soon as you start to notice symptoms and according to the dosing instructions given to you by your healthcare provider.