Valacyclovir: Important Side Effects and Warnings To Know

Valacyclovir (Valtrex) is prescribed for the treatment of infections caused by the herpes virus, including genital herpes, shingles, and cold sores.

Although valacyclovir does not cure genital herpes or shingles, it can relieve the pain and discomfort and heal the sores faster

Like all medications, Valacyclovir can cause potential side effects.

This article discusses the common warnings and side effects of valacyclovir and how to manage them.

What Are The Side Effects Of Valacyclovir?

Here are some side effects commonly reported by patients treated with Valtrex.

1) Nausea and vomiting

It is common for patients to experience digestive problems, such as nausea and vomiting, while using Valacyclovir.  

These symptoms are often accompanied by pain in the abdomen, indigestion, bloating, and flatulence.

These potential side effects of Valtrex are usually mild and often resolve spontaneously within a few days after discontinuing the medication.

Taking your medication after food, avoiding the intake of fried or spicy foods, and drinking enough water can also help to relieve these side effects.

2) Blood disorders

Valacyclovir can sometimes cause blood disorders such as thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS).

Thrombocytopenic purpura is characterized by a decline in the number of platelets in the blood. Platelets play a key role in clot formation, thus preventing excess bleeding in the event of trauma or injury. 

A decrease in platelet count can result in bleeding gums, easy bruising, and an increased risk of internal bleeding.

Hemolytic uremic syndrome occurs when small blood vessels become inflamed and damaged. This leads to the formation of clots in the vessels throughout the body. These clots can damage the vital organs such as the kidneys.

TTP and HUS are serious, potentially life-threatening conditions. The risk of these Valtrex side effects is higher in patients who have had a kidney or bone marrow transplant. The risk is also higher in patients with advanced HIV or AIDS.

If you have these conditions, consult your doctor for advice on alternative treatments for managing herpes infection.

Also, if you notice any signs of thrombocytopenic purpura and hemolytic uremic syndrome while using Valacyclovir, inform your doctor immediately. 

Your doctor will advise you on whether to continue using the drug or suggest a change in dosage or medication.

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3) Kidney failure

Valacyclovir may impact kidney function, particularly if taken in higher doses or with other drugs harmful to the kidneys. The risk is higher in individuals with pre-existing kidney ailments.

The risk of kidney failure is particularly higher when Valacyclovir is used with other drugs that harm the kidneys or if you are not well hydrated. 

People over the age of 65 years are also more likely to develop these side effects.

Some common signs of kidney failure include:

  • Reduced frequency of urination
  • Passing too little urine than usual
  • Swelling of the hands, feet, ankles, or face
  • High blood 
  • pressure

If you notice these signs of kidney failure, inform your doctor right away. Your doctor might ask you to do renal function tests to assess kidney function and advise you on whether to continue or stop using Valacyclovir.

4) Hallucinations

If you use Valacyclovir in higher doses or have kidney disease, the medication will build up in your body. 

The high levels of Valacyclovir in your system might affect your brain and cause neurotoxicity. This can result in serious side effects such as hallucinations (hearing or seeing things that are not real) and delusions (believing things that are not true).

Some other neurological symptoms associated with the build-up of Valacyclovir include confusion, agitation, and seizures. 

If you have any of these Valtrex side effects, you must stop taking this drug and visit the nearest emergency room.

5) Unusual mood

Some patients have reported experiencing unusual moods and behavior while using Valtrex. These symptoms are often accompanied by aggressive behavior, mood swings, feeling low, unsteady or shaky movements, confusion, and hallucinations.

These side effects are usually temporary and go away after stopping the drug. Practicing stress-relieving methods such as yoga and meditation and following a fixed bedtime routine to ensure you are not sleep-deprived are some ways to improve your mood and lower the impact of the drug on your emotional wellness.

How Long Do The Side Effects Of Valtrex Last?

The side effects of Valacyclovir associated with the digestive system and mental health are usually temporary, lasting a few days to weeks. 

However, the side effects related to the involvement of the kidneys, blood, and nervous system might last longer.

What Are The Long-Term Side Effects Of Valacyclovir?

Valacyclovir can cause a few long-term side effects, although rarely.

For example, valacyclovir may affect the functions of the kidneys and cause renal failure. 

The development of blood disorders such as thrombocytopenic purpura and hemolytic uremic syndrome can also last for several weeks after stopping the use of this drug. 

Valacyclovir may also cause changes in your thinking and behavior, resulting in confusion, delusions, disorientation, or hallucinations. 

These side effects might continue to persist for a few weeks to months, even after you stop the medication.

Therefore, it is advisable to be watchful of the signs of these valacyclovir side effects and inform your doctor if you experience them.

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Can You Take Valacyclovir Daily?

The dosage of Valacyclovir depends on the type of herpes infection to be treated and the severity of the symptoms. 

In most cases, it needs to be taken twice daily, and the treatment typically lasts from 1 to 14 days, depending on the condition that’s being treated and the patient’s immunocompetency.

If you have recurrent exacerbations of genital herpes, you might need to take 500 mg of Valacyclovir (Valtrex) two times a day for 3 days.

Do You Have to Take Valacyclovir Every Day for the Rest of Your Life?

No, you do not have to take Valacyclovir every day for the rest of your life. Valacyclovir is not meant to be taken on a regular basis. 

What are the Side Effects of Stopping Valacyclovir? 

Abruptly stopping Valacyclovir before completing the prescribed course may worsen the symptoms of your viral infection.

Is It Bad To Stop Taking Valacyclovir?

You must keep taking valacyclovir for the full course of treatment, even if your symptoms have cleared up. This will help eliminate the infection completely and reduce your risk of flare-ups. 

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Valacyclovir Warnings

Valacyclovir comes with several warnings, some of which include:


Valacyclovir has the potential to cause an allergic reaction, characterized by symptoms such as itching, skin rash, difficulty breathing, and swelling of the face, throat, or tongue.

If you develop these signs, stop using the drug and go to the nearest emergency room.

Advanced HIV or AIDS

If you have advanced HIV or AIDS, you should avoid using Valacyclovir as it might increase your risk of serious side effects such as thrombocytopenic purpura and hemolytic uremic syndrome. 

Kidney or bone marrow transplantation

The risk of blood disorders due to Valacyclovir is higher in patients who have a kidney or bone marrow transplant. 

Hence, you must inform your doctor if you have had a transplant and ask if you need an alternative prescription for herpes infection.


There is no clarity on the safety of Valacyclovir when used by pregnant women, although it has not been shown to cause birth defects in the baby. So, talk to your doctor if you are pregnant or planning to become pregnant before using Valacyclovir. 


Valacyclovir may pass into breast milk and cause side effects in a child. So, talk to your doctor if you are breastfeeding your child. 

Elderly patients

The functions of the kidneys are likely to be impaired in older adults. This can cause the body to process Valacyclovir more slowly, allowing for a higher amount of the drug to stay in the body for a longer duration. This can increase their risk of adverse effects.

Hence, elderly people should refrain from using Valacyclovir unless advised by a physician.

Pediatric patients

Valacyclovir has not been studied extensively for use in the treatment of herpes simplex virus infection in the pediatric group of patients. 

It is not approved for the treatment of shingles in children below 18 years and chickenpox in children below 2 years of age.

Parents should consult a pediatrician before administering Valacyclovir to their kids.


  • Valacyclovir is a medication used for treating herpes infections. 
  • Being aware of the side effects and warnings associated with Valacyclovir is essential to ensure the optimum safety and effectiveness of the drug.

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  1. Lebrun-Vignes B. Valaciclovir [Valaciclovir]. Ann Dermatol Venereol. 2002 May;129(5 Pt 1):708-15. French. PMID: 12124513.
  2. Mother To Baby | Fact Sheets [Internet]. Brentwood (TN): Organization of Teratology Information Specialists (OTIS); 1994-. Acyclovir (Zovirax®) / Valacyclovir (Valtrex®) 2022 Apr.
  3. Gublo B, St Amand AB, Menon A, Scalise AA. Valacyclovir Neurotoxicity in Patients with End-Stage Renal Disease: Two Cases Reviewed. J Pharm Pract. 2024 Feb;37(1):248-251. doi: 10.1177/08971900221127061. Epub 2022 Sep 13. PMID: 38247339.

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