Valtrex side effects, interactions, warnings, and how to avoid them

In this article:

• What is Valtrex?
• Common side effects
• Serious side effects
• Warnings
• Interactions
• How to avoid side effects

In this article

• What is Valtrex?
• Common side effects
• Serious side effects
• Warnings
• Interactions
• How to avoid side effects

If you’ve ever had shingles or cold sores, you know how uncomfortable these infections can be. Valtrex is an antiviral medication that can help relieve symptoms from viral infections like shingles or chickenpox. This article gives an overview of drug information, including Valtrex side effects, warnings, and drug interactions that you should be aware of before taking the medication. 

What is Valtrex?

Valtrex belongs to a group of medications called antivirals that work by slowing down the growth and spread of viruses like herpes simplex, herpes zoster, and varicella-zoster viruses. Valtrex is the brand name for valacyclovir hydrochloride. The brand and generic versions of the medication are chemically the same, work the same way, and are equally effective at treating herpes virus infections.

Herpes virus infections include cold sores, genital herpes, shingles, and chickenpox. Valtrex can’t cure herpes infections but can help treat symptoms like herpes sores and blisters. Valtrex is not an over-the-counter medication, so if you have a herpes infection, you’ll need a prescription. 

Valtrex can take up to seven to 10 days to start working for some people, while others may feel relief from their symptoms after a day or two. The amount of time it takes your symptoms to go away will depend on factors such as your age, severity, and metabolism.

Valtrex for cold sores

Many people wonder whether Valtrex will stop cold sores from forming. Valtrex should be taken at the first signs of a cold sore (tingling, itching, burning) to prevent them from worsening and keep other cold sores from developing. However, it is not a cure for cold sores. It only treats them as a symptom of a viral infection.

Valtrex for genital herpes

Even if you’re taking Valtrex, it’s still possible to have an outbreak. If you’re taking Valtrex for recurrent genital herpes and have an outbreak, it’s important to avoid sexual contact with your partner to keep the virus from spreading to them. Even if you’re not experiencing an outbreak, using condoms is important to help prevent transmission of the herpes virus. 

Also, if you’re wondering if your uninfected partner can take Valtrex to avoid becoming affected, the answer is no. Someone without herpes simplex virus shouldn’t take medication for something they don’t have. This could cause serious side effects or health problems. 

Common side effects of Valtrex 

Taking Valtrex may cause possible side effects, such as: 

• Headache 
• Nausea
• Stomach pain or abdominal pain 
• Dizziness
• Vomiting 
• Irritability 
• Tiredness
• Skin rash 
• Sore throat 
• Diarrhea 
• Joint pain 

Headache

Headache is a common side effect of Valtrex. If you experience a mild headache while taking Valtrex, you can try nonmedicinal measures such as increasing fluid intake and resting in a cool, dark, quiet room. If needed, you can ask your doctor or pharmacist about an appropriate over-the-counter (non-prescription) medication. If your headache is persistent or very painful, consult your doctor.

Nausea

Nausea is a common side effect of Valtrex. Gastrointestinal side effects like nausea often resolve within a day or two. Consult your doctor if the nausea is severe and/or causes vomiting. If the nausea is mild, you can stick to foods and drinks that help settle your stomach, such as crackers and ginger ale. Avoid spicy, heavy, fatty, and fried foods. You can ask your pharmacist for Emetrol or cola syrup. 

It’s unknown whether Valtrex causes other adverse effects, such as weight gain, dry mouth, or any other symptoms not listed by the United States Food and Drug Administration (FDA). This is not a complete list of side effects. Other side effects may occur. Consult your healthcare provider if you have questions about the side effects of Valtrex.

A frequently asked question about Valtrex is whether it will make you urinate more often. It won’t necessarily make you pee more, but you should drink plenty of water while taking Valtrex to help the kidneys process it as best they can. Therefore, this extra hydration can result in frequent urination.

Serious side effects of Valtrex

Although it’s rare, Valtrex can cause more serious side effects that may require medical help, including:

• Kidney failure
• Nervous system problems: agitation, hallucinations, confusion, aggressive behavior, seizures, speech problems
• Unusual bruising or bleeding 
• Depression
• Low blood cell counts
• Painful periods for women 
• Liver problems
• A serious blood disorder called thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) 

If you have any signs of an allergic reaction, such as difficulty breathing, hives, or swelling of the face, mouth, or throat, you should seek immediate emergency medical treatment. 

Some patients are more susceptible to these serious side effects than others. Consult your healthcare provider to find out if you’re at risk.

These side effects are very rare. Antiviral medicines are effective at treating viral infections, but after long-term use, they can eventually weaken the immune system by affecting immune cells, especially in older adults and people with weakened immune systems. Even though they’re not typically taken for long periods, if your doctor wants you to take them long-term, that’s okay. Some studies have even shown that the long-term use of Valtrex is well-tolerated for healthy individuals.

If you start to have side effects from Valtrex and are thinking about stopping the medication, you should call your doctor before doing so. Abruptly stopping Valtrex can cause new side effects or worsen symptoms. If you stop Valtrex before you’re supposed to, your viral infection may get worse because the medication hasn’t had the opportunity to work properly. 

Kidney failure

Before taking Valtrex, tell your doctor if you have any kidney problems or have ever had a kidney transplant. While taking Valtrex, drink plenty of water to help keep your kidneys work properly. Be alert to signs of kidney problems, such as urinating less frequently, tiredness, shortness of breath, and swelling in the feet or ankles.

Nervous system problems

Valtrex can cause nervous system problems. Reactions can include agitation, hallucinations, seizures, confusion, speech problems, and aggressive behavior. Nervous system problems are more likely to occur in older adults and/or people with kidney problems. Contact your healthcare provider or seek emergency medical care if these symptoms occur. Valtrex should be discontinued if nervous system problems occur. 

If you’re taking Valtrex and have any of these symptoms, you should contact your doctor for medical advice as soon as possible. 

Valtrex warnings

Even though Valtrex is very effective at treating herpes virus infections, it shouldn’t be taken by everyone. You should talk with your doctor before taking Valtrex if you have any of the following medical conditions:

• HIV: Having HIV suppresses the immune system, making it harder to fight infections and increasing the probability of getting certain other medical conditions. People with HIV who take Valtrex may have an increased risk of getting TTP/HUS—a serious blood disorder. 
• Kidney or bone marrow transplants: If you’re taking Valtrex and are about to have a bone marrow or kidney transplant, you should talk with your doctor. Your risk of getting TTP/HUS may be increased if you take Valtrex during your transplant process.
• Kidney problems or kidney disease: People with kidney problems or kidney disease could experience a worsening of symptoms or kidney failure if they take Valtrex.

Because of its potential to negatively affect the kidneys, some people wonder if Valtrex is also hard on the liver, but studies have shown that it’s rarely associated with mild liver injury that resolves quickly. 

If you are over the age of 65, it’s best to consult with your doctor before taking Valtrex. Older adults may have a higher risk of experiencing certain side effects and are more likely to have kidney problems. This doesn’t mean that if you’re over 65, you can’t take Valtrex. Your doctor may simply recommend a lower dose to reduce this risk.

Pregnant women should talk with a healthcare professional if they’re considering taking Valtrex to learn how it might affect their pregnancy. “Through laboratory testing, Valtrex had no effects on the fetus; nevertheless, Valtrex was not adequately tested with pregnant people,” says Vikram Tarugu, MD, a gastroenterologist and the CEO of Detox of South Florida. “The safety of Valtrex has not been proven in breastfeeding babies.” Women who are breastfeeding should consult their doctor for medical advice about taking Valtrex. 

Valtrex interactions

Taking Valtrex at the same time as certain other medications may cause additional side effects or complications. You should talk with your doctor before taking Valtrex if you’re on any of these medications: 

• Foscarnet 
• Acyclovir 
• Famciclovir
• Nephrotoxic agents (drugs that can harm the kidneys)
• Methotrexate 
• Cancer medications (chemotherapy)
• Arthritis medications that affect the immune system
• Medications used to prevent organ transplant rejections 
• Also, talk to your doctor if you’ve recently had a varicella virus vaccine (live) 

Bring a complete list of all the prescription drugs and supplements you’re taking to your healthcare provider so they can decide if Valtrex is right for you. 

There are currently no known interactions between Valtrex and grapefruit or grapefruit juice, which can sometimes interfere with how much of a drug stays in the body at one time. 

Alcohol, on the other hand, is best avoided while taking Valtrex. This is because when alcohol and Valtrex are combined, they can cause excessive drowsiness and dizziness. 

When it comes to caffeine and Tylenol, two of the things most likely to be consumed while on Valtrex, it’s okay to take them unless told otherwise by a medical professional.

How to avoid Valtrex side effects

Taking the right dose at the right time of day is the best way to avoid Valtrex side effects. Here are the standard doses of Valtrex for adults and children: 

These dosages are only general guidelines. If your doctor prescribes Valtrex differently, then you should follow their instructions. Valtrex is most effective when started as soon as symptoms begin, so see your doctor immediately if you have symptoms. It’s safe to take Valtrex every day as long as you’ve been instructed to do so.

If you miss a dose of Valtrex, you should take the missed dose as soon as possible. Taking your missed dose as soon as you remember you’ve missed it will help keep your herpes infection from worsening. Taking two doses at one time can cause serious side effects, so if you’ve missed a dose, only take one dose when you remember. However, if it’s almost time for your next dose, skip the missed dose and resume your normal schedule. 

Taking Valtrex with a full glass of water helps your kidneys process it more efficiently. Once it’s been taken, Valtrex starts working to treat symptoms right away. Even though it starts working right away, it may take several days for you to notice a difference in your symptoms. Take Valtrex exactly as prescribed by your healthcare provider.

It’s also important to remember that Valtrex has an expiration date, just like any other medication. Look for the expiration date on the prescription label to see how long your particular version of Valtrex is good for. Expired medications can be less effective and risky to take. Some medications are also sensitive to heat, so store Valtrex at room temperature.

Switching medications is also an option. Acyclovir (brand name Zovirax) is another antiviral drug that can treat herpes virus and varicella-zoster virus infections. Neither medication is better than the other, but if someone can’t tolerate Valtrex or has an underlying medical condition that prevents them from taking it, acyclovir is another good option. You can compare the medications here.