Can Valacyclovir Cause Hives? Understanding the Connection

October 9, 2025 •

3 min read

While generally well-tolerated, postmarketing reports confirm that valacyclovir can cause hives (urticaria) as part of an allergic reaction. Hives are a known, though not frequent, side effect of this widely used antiviral medication.

Quick Summary

Yes, the antiviral medication valacyclovir can cause hives. Hives are a sign of an allergic reaction that requires immediate medical attention. This reaction can also include swelling, itching, and difficulty breathing.

Key Points

Hives Are a Sign of Allergy: Yes, valacyclovir can cause hives (urticaria), which is a sign of an allergic reaction.
Immediate Action Required: If you develop hives, swelling, or difficulty breathing while on valacyclovir, seek emergency medical help immediately.
Cross-Allergy Exists: People allergic to acyclovir should not take valacyclovir, as it is converted to acyclovir in the body.
Common vs. Severe Side Effects: Common side effects include headache and nausea, while severe ones include allergic reactions and nervous system changes.
DRESS Syndrome: In very rare instances, valacyclovir has been linked to a severe, life-threatening skin reaction called DRESS syndrome.
Stay Hydrated: Drinking plenty of water while taking valacyclovir is important to help your kidneys function properly and reduce the risk of kidney-related side effects.
Alternatives Are Available: If you are allergic to valacyclovir, alternative antiviral medications like famciclovir are available.

What is Valacyclovir?

Valacyclovir is an oral antiviral medication used to manage infections caused by herpes viruses, including HSV-1, HSV-2, and varicella-zoster virus (the cause of chickenpox and shingles). It is a prodrug that the body converts into acyclovir. This conversion improves absorption and allows for less frequent dosing than acyclovir. Valacyclovir works by interfering with viral DNA synthesis, slowing the virus's growth and spread. Its action is primarily in infected cells.

Can Valacyclovir Cause Hives (Urticaria)?

Valacyclovir can cause hives (urticaria). Hives are a sign of an allergic reaction, appearing as raised, itchy welts. While not a common side effect, hives and other skin rashes are potential adverse reactions that need medical attention.

Symptoms of a serious allergic reaction, also called anaphylaxis, include hives or skin rash, itching, swelling of the face, lips, tongue, or throat, and difficulty breathing or tightness in the chest. Wheezing or unusual hoarseness can also occur. Emergency medical help is required if these symptoms appear. Individuals with an acyclovir allergy should not take valacyclovir.

Other Serious Skin Reactions

In rare cases, valacyclovir can cause severe skin conditions like Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) syndrome. DRESS is a severe hypersensitivity reaction with a widespread rash and fever that can affect internal organs, typically starting 2 to 8 weeks after beginning medication. Other rare severe skin reactions linked to valacyclovir include erythema multiforme and photosensitivity-related rashes.

Valacyclovir Side Effects: Common vs. Severe

It's important to distinguish between typical side effects and more serious ones.


Side Effect Category	Examples	Action Required
Common Side Effects	Headache, nausea, stomach pain, dizziness, diarrhea.	Usually do not require medical attention unless persistent or bothersome. Hydration can help.
Serious Side Effects	Hives, skin rash, itching, swelling (allergic reaction). Confusion, hallucinations, agitation (nervous system effects). Kidney problems (decreased urination, swelling).	Stop medication and call your doctor or seek emergency help immediately.
Rare, Severe Reactions	Signs of DRESS syndrome, Stevens-Johnson syndrome, or Toxic Epidermal Necrolysis (blistering, peeling skin).	Seek immediate emergency medical treatment. These conditions are life-threatening.

What to Do If You Experience Hives

If you get hives or other allergic reaction signs while taking valacyclovir, stop the medication and contact your healthcare provider immediately.

Stop the Medication: Do not take more doses.
Seek Medical Advice: Contact your doctor or seek emergency care, especially with swelling, breathing difficulty, or dizziness.
Symptom Management: Your doctor may suggest antihistamines for itching and hives. Corticosteroids may be used for more severe inflammation.

Alternatives to Valacyclovir

Alternative antiviral medications are available for those who cannot take valacyclovir.

Acyclovir (Zovirax): As valacyclovir converts to acyclovir, an allergy to one usually means an allergy to both. Acyclovir is an alternative if tolerated, requiring more frequent doses.
Famciclovir (Famvir): Another oral antiviral often used as an alternative.

Choosing an alternative requires consulting a healthcare provider.

Conclusion

Valacyclovir is an effective antiviral that can cause hives as part of an allergic reaction. Recognizing signs like hives, rash, and swelling is important. Hives require immediate discontinuation and medical consultation. Find more information on drug-induced skin reactions {Link: American Academy of Dermatology https://www.aad.org/public/diseases/a-z/drug-rashes}.

Frequently Asked Questions

An allergic reaction like hives can occur shortly after taking the medication, but drug-induced urticaria can appear anywhere from 1 to 24 hours after ingestion. In some rare, severe reactions like DRESS syndrome, a rash might not appear until 2 to 8 weeks after starting the drug.

Hives are not one of the most common side effects. The most frequently reported side effects are headache, nausea, and abdominal pain. Hives are considered a less common but important side effect indicating a potential allergy.

If you get any type of skin rash, hives, or itching while taking valacyclovir, you should report it to your healthcare team as soon as possible. These can be signs of an allergic reaction.

While an antihistamine like diphenhydramine (Benadryl) can help treat hives, you must first contact your doctor before taking any new medication. Your doctor needs to confirm the cause of the hives and determine the appropriate treatment plan.

Yes, it is very likely. Valacyclovir is a 'prodrug' that your body converts into acyclovir. An allergic reaction to valacyclovir is a reaction to acyclovir, so you should avoid both medications.

A rash from a valacyclovir allergic reaction can appear as hives (raised, itchy welts) or a more generalized red, itchy rash. In rare cases, it could be part of a more severe reaction involving blistering or peeling skin.

Serious side effects that require immediate medical attention include signs of an allergic reaction (hives, swelling, trouble breathing), kidney problems (change in urination), and central nervous system effects like confusion, hallucinations, or seizures.