Valtrex Side Effects and Contraindications

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Most of us are used to the litany of side effects that are listed in fine print with any given drug. Valtrex is no exception, as it has common and rare side effects as well as contraindications with some diseases. Although it’s a great choice for treating outbreaks, it’s good to know.

Read on to learn which Valtrex side effects are common, moderate or rare, and what other potential adverse reactions there are. This isn’t meant to be a substitute for medical advice. Please consult a physician.

Valtrex Side Effects and Reactions

Valtrex Uses

Valtrex is an antiviral medication usually prescribed for several types of herpes viruses. It’s used to treat herpes and shingles. Its generic name is valacyclovir.

Valtrex is popular because it can clear up an outbreak if treated soon enough. It’s also marketed for daily suppressive therapy, which means taking Valtrex daily. Doing so reduces the number of outbreaks as well as the likelihood of transmission to one’s partner by about half.

Common Valtrex Side Effects

There are officially listed common side effects as well as people’s testimonies.

Going by personal testimonies online, it seems the most commonly cited Valtrex side effects include itchy skin, dehydration and thirst, and mild disorientation in some people.

In fact, the information that comes with Valtrex warns that you should not drive a car or operate heavy machinery until you know the effects of the drug on you.

Here are listed side effects:

Common adverse drug reactions (≥1% of patients) include:

nausea, vomiting, diarrhea and headache.

Infrequent adverse effects (0.1–1% of patients) include:

agitation, vertigo, confusion, dizziness, edema, arthralgia, sore throat, constipation, abdominal pain, rash, weakness and/or renal impairment.

Rare adverse effects (<0.1% of patients) include:

coma, seizures, neutropenia, leukopenia, tremor, ataxia, encephalopathy, psychotic symptoms, crystalluria, anorexia, fatigue, hepatitis, Stevens–Johnson syndrome, toxic epidermal necrolysis and/or anaphylaxis.

Valtrex and the Liver

Generic Valtrex: ValocyclovirThe dosage for daily suppressive therapy is one gram per day. Two grams are taken only when there is an active outbreak. However, daily use is too much for some people who are concerned about the effect of such a heavy dose on the liver, since that is where Valtrex is processed. Therefore they only take it when they have an outbreak. Liver damage can show up as inflammation of the liver, abnormal enzymes, or hepatitis. (It’s generally agreed that no one should take Valtrex forever, especially not in high doses.)

Valtrex and the Kidneys

Over time, the cumulative effects of taking Valtrex can damage the kidneys as well as the liver. In tests, Valtrex was shown to cause acute kidney failure in certain patients. Those who experienced these Valtrex side effects to the kidneys:

  1. had previously existing kidney conditions;
  2. were elderly without previous kidney conditions; or
  3. also taking other medications that affect the kidneys.

Central Nervous System Effects

Valtrex has been linked to reports of dizziness, hallucinations, agitation, confusion, delirium, seizures and encephalopathy in some patients. These adverse reactions are more likely to occur in elderly patients.

Valtrex and Pregnancy

Valtrex is considered a “Category B” medication, which means there are no known risks for taking Valtrex during pregnancy or breastfeeding in humans. Doctors will sometimes prescribe Valtrex during pregnancy if they believe there is a risk of an outbreak during labor, in order to prevent transmission to the baby.

However, the testing necessary to receive category B status was only done on 749 women. Even the maker of Xanax, GlaxoSmithKline, states in its Valtrex information that this study size is not adequate. It reads:

“There are no adequate and well-controlled trials of VALTREX or acyclovir in pregnant women. Based on prospective pregnancy registry data on 749 pregnancies, the overall rate of birth defects in infants exposed to acyclovir in-utero appears similar to the rate for infants in the general population. … VALTREX should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. …However, the small size of the registry is insufficient to evaluate the risk for less common defects or to permit reliable or definitive conclusions regarding the safety of acyclovir in pregnant women and their developing fetuses… A 500 mg maternal dosage of VALTREX twice daily would provide a nursing infant with an oral acyclovir dosage of approximately 0.6 mg/kg/day. … Caution should be exercised when VALTREX is administered to a nursing woman.”

Valtrex Contraindications

Certain previously existing conditions can make Valtrex a poor option for some patients. Valtrex is known to cause moderate to severe complications for people with the following conditions:

  • Renal impairment
  • Ttp/Hus
  • Hemodialysis

Valtrex and Alcohol

Some people report an increased incidence of “black-outs” when drinking while on Xanax. Comments by people online suggest that in some people, it takes less alcohol to become overly intoxicated and even black out, losing memory of what occurred while under the influence.

Full Possible Side Effects List

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop taking valacyclovir and call your doctor right away if you have any of the following signs of a serious side effect that can harm red blood cells:

  • fever, easy bruising or bleeding;
  • red spots on the skin (not related to herpes or chickenpox);
  • bloody diarrhea, vomiting;
  • pale or yellowed skin;
  • weakness or fainting; or
  • urinating less than usual or not at all.

Call your doctor at once if you have any of these other serious side effects:

  • pain in your lower back;
  • drowsiness, mood changes, increased thirst, loss of appetite, nausea and vomiting;
  • swelling, weight gain, feeling short of breath;
  • confusion, agitation, aggression, hallucinations, trouble concentrating;
  • feeling shaky or unsteady;
  • problems with speech or vision; or
  • seizure (convulsions).

Less serious side effects may include:

  • nausea, stomach pain;
  • headache, dizziness, tired feeling, depression;
  • joint pain;
  • menstrual pain;
  • mild skin rash; or
  • stuffy nose, sore throat.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. You may report side effects to FDA at 1-800-FDA-1088.


Valtrex (valocyclovir) and acyclovir are effective antiviral prescription medications for treating several types of herpes. Valtrex can stop outbreaks if taken when signs show up, or even reduce their occurrence if taken daily. Nonetheless, one should discuss their conditions and any medical concerns with their doctor honestly, to see if any Valtrex side effects are very likely to affect them. For many, there are natural ways to control herpes outbreaks, such as eating a healthy diet low in arginine, or using home herbal/natural remedies.