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Zovirax Side Effects

Generic name: acyclovir

Medically reviewed by Last updated on Jun 23, 2023.

Note: This document contains side effect information about acyclovir. Some dosage forms listed on this page may not apply to the brand name Zovirax.

Applies to acyclovir: buccal mucosa tablet. Other dosage forms:

Serious side effects of Zovirax

Along with its needed effects, acyclovir (the active ingredient contained in Zovirax) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking acyclovir:

Less common

Other side effects of Zovirax

Some side effects of acyclovir may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

For Healthcare Professionals

Applies to acyclovir: buccal tablet, compounding powder, intravenous powder for injection, intravenous solution, oral capsule, oral suspension, oral tablet.


The more commonly reported adverse reactions include malaise, nausea, vomiting, diarrhea, and headache.[Ref]


Nausea and vomiting are more frequent in elderly subjects.[Ref]

Common (1% to 10%): Nausea, vomiting, diarrhea, abdominal pain, gingival pain (buccal tablet), aphthous stomatitis (buccal tablet)

Uncommon (0.1% to 1%): Sore throat

Postmarketing reports: Gastrointestinal distress[Ref]


Renal pain may be associated with renal failure and crystalluria. Renal impairment is generally reversible but may progress to acute renal failure.[Ref]

Rare (0.01% to 0.1%): Elevated blood urea nitrogen, elevated creatinine,

Very rare (less than 0.01%): Acute renal failure, renal pain

Frequency not reported: Crystalluria, renal impairment

Postmarketing reports: Renal failure, hematuria[Ref]


Severe local inflammatory reactions, including tissue necrosis, have occurred following infusion into extravascular tissues. Application site pain and application site irritation have occurred with the buccal tablets.[Ref]

Common (1% to 10%): Application site pain and application site irritation, local inflammation at injection site, phlebitis

Frequency not reported: Tissue necrosis[Ref]

Nervous system

Dizziness, somnolence, and coma more frequent in elderly subjects.[Ref]

Common (1% to 10%): Headache, dizziness

Very rare (less than 0.01%): Ataxia, coma, convulsions, encephalopathy, dysarthria

Frequency not reported: Giddiness, shaking, taste disturbance, medication taste

Postmarketing reports: Decreased consciousness, delirium, paresthesia, seizure, tremors[Ref]


Common (1% to 10%): Erythema, rashes (including photosensitivity), pruritus, hives

Uncommon (0.1% to 1%): Urticaria, accelerated diffuse hair loss

Frequency not reported: Diaphoresis

Postmarketing reports: Alopecia, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis[Ref]


Frequency not reported: Palpitation, chest pain

Postmarketing reports: Hypotension, peripheral edema[Ref]


Very rare (less than 0.01%): Anemia, leukopenia, thrombocytopenia, neutropenia

Frequency not reported: Hematologic changes including megaloblastic anemia

Postmarketing reports: Leukocyclastic vasculitis, lymphadenopathy, disseminated intravascular coagulation, hemolysis[Ref]


Rare (0.01% to 0.1%): Reversible bilirubin and liver related enzymes

Very rare (less than 0.01%): Hepatitis, jaundice

Postmarketing reports: Hyperbilirubinemia[Ref]


Rare (0.01% to 0.1%): Anaphylaxis

Frequency not reported: Angioedema[Ref]


Frequency not reported: Pars planitis

Postmarketing reports: Visual abnormalities[Ref]


Uncommon (0.1% to 1%): Leg pain

Postmarketing reports: Myalgia[Ref]


Common (1% to 10%): Lethargy, fatigue, fever

Frequency not reported: Vertigo

Postmarketing reports: Fever[Ref]


Frequency not reported: Menstrual abnormalities, abnormal urinalysis (characterized by an increase in formed elements in urine sediment) anuria, dysuria, hematuria[Ref]


Uncommon (0.1% to 1%): Anorexia

Frequency not reported: Thirst[Ref]


Very rare (less than 0.01%): Agitation, confusion, hallucinations, psychotic symptoms

Frequency not reported: Depression, insomnia

Postmarketing reports: Aggressive behavior[Ref]

Hallucinations, psychosis, confusion, aggressive behavior, agitation may be more marked in older adults and those with renal impairment.[Ref]


Rare (0.01% to 0.1%): Dyspnea[Ref]

Frequently asked questions


1. Cerner Multum, Inc. UK Summary of Product Characteristics.

2. Cerner Multum, Inc. Australian Product Information.

3. Product Information. Sitavig (acyclovir). Innocutis Holdings LLC. 2017.

4. Product Information. Acyclovir (acyclovir). West-Ward Pharmaceuticals Corporation (previously Roxane Laboratories Inc). 2017.

5. Product Information. Zovirax (acyclovir). Mylan Pharmaceuticals Inc. 2017;PROD.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.