What is the difference between Acyclovir and Valacyclovir?

Acyclovir and Valacyclovir are both Antiviral (Herpes)s, so they work through the same broad mechanism. They differ in dosing, half-life, side-effect frequency, and how individual patients tolerate them. See the head-to-head sections below for the specifics.

Can Acyclovir and Valacyclovir be used for the same conditions?

Both medications are prescribed for overlapping indications including See full prescribing information. Always verify with your prescriber and the current FDA label before switching.

Is Acyclovir the same as Valacyclovir?

No. Acyclovir (Acyclovir) and Valacyclovir (Valacyclovir) are distinct medications. They are sometimes confused because of similar branding or because they treat overlapping conditions, but they have different active ingredients and different safety profiles.

Which has fewer side effects, Acyclovir or Valacyclovir?

Side-effect frequency varies by individual. The side-effect comparison section on this page shows FAERS-reported events for each drug side by side. FAERS is voluntary reporting, so it reflects what patients and clinicians chose to report, not absolute population risk.

Can I switch from Acyclovir to Valacyclovir?

Switching medications should always be done under prescriber supervision. The "patient stories" section on this page includes accounts from people who have made the switch and what their transition felt like, but those are individual experiences, not protocols.

Acyclovir vs Valacyclovir

Compare Acyclovir (Acyclovir) and Valacyclovir (Valacyclovir), clinical data, side effects, and patient experiences.

Acyclovir

Acyclovir, Zovirax, Xerese · Antiviral (Herpes)

How it works

Mechanism of Antiviral Action: Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HS...

Approved for

See full prescribing information

OralTablet

Valacyclovir

Valacyclovir, Valtrex · Antiviral (Herpes)

How it works

12.1 Mechanism of Action Valacyclovir is an antiviral drug active against α-herpes viruses [see Microbiology (12.4) ].

Approved for

papule

vesicle

papule

vesicle

OralTablet

Quick Comparison

AcyclovirValacyclovir

Drug Class

Antiviral (Herpes)

Route

Oral

Half-Life

N/A

FDA Approved

N/A

Pregnancy

N/A

Side Effect Frequency Comparison

Estimated frequency (%) based on clinical trial data

Side Effects

Acyclovir

Fatigue

>10%

Diarrhea

>10%

Nausea

1-10%

Fever

1-10%

Drug Not Working

1-10%

Rash

1-10%

Shortness of Breath

1-10%

Weakness

0.1-1%

Valacyclovir

Fatigue

1-10%

Drug Not Working

1-10%

Nausea

1-10%

Diarrhea

1-10%

Headache

1-10%

Fever

1-10%

Rash

1-10%

Dizziness

1-10%

FDA Warnings

Acyclovir

WARNINGS Acyclovir capsules are intended for oral ingestion only
Renal failure, in some cases resulting in death, has been observed with acyclovir therapy (see ADVERSE REACTIONS: Observed During Clinical Practice and OVERDOSAGE )
Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), which has resulted in death, has occurred in immunocompromised patients receiving acyclovir therapy

Valacyclovir

5 WARNINGS AND PRECAUTIONS Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS): Has occurred in patients with advanced HIV-1 disease and in allogenic bone marrow transplant and renal transplant patients receiving 8 grams per day of valacyclovir tablets in clinical trials
1 Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome (TTP/HUS) TTP/HUS, in some cases resulting in death, has occurred in patients with advanced HIV-1 disease and also in allogeneic bone marrow transplant and renal transplant recipients participating in clinical trials of valacyclovir tablets at doses of 8 grams per day

Clinical Trial Data

No head-to-head clinical studies found for Acyclovir vs Valacyclovir.

Acyclovir vs Valacyclovir: What You Should Know

Key Differences

Both Acyclovir and Valacyclovir belong to the Antiviral (Herpes) class. While they share a similar mechanism of action, differences in pharmacokinetics, dosing, and side effect profiles may make one more suitable than the other for individual patients.

Safety Considerations

Acyclovir carries 3 FDA warnings. Valacyclovir carries 2 FDA warnings. Patients should discuss all warnings and contraindications with their healthcare provider before starting or switching medications..

This comparison is for informational purposes only. Always consult a qualified healthcare professional before making medication decisions.

Related Comparisons

Acyclovir vs Famciclovir→Famciclovir vs Valacyclovir→Acyclovir vs Valacyclovir Hydrochloride→Valacyclovir vs Valacyclovir Hydrochloride→Acyclovir vs Acyclovir Sodium→Acyclovir Sodium vs Valacyclovir→

Primary sources

Every figure on this comparison links back to its primary source. See data sources and methodology for the full provenance trail.

Acyclovir: DailyMed label · FAERS adverse events · ClinicalTrials.gov
Valacyclovir: DailyMed label · FAERS adverse events · ClinicalTrials.gov

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Acyclovir vs Valacyclovir

Compare Acyclovir (Acyclovir) and Valacyclovir (Valacyclovir), clinical data, side effects, and patient experiences.

Acyclovir

Acyclovir, Zovirax, Xerese · Antiviral (Herpes)

How it works

Mechanism of Antiviral Action: Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HS...

Approved for

See full prescribing information

OralTablet

Valacyclovir

Valacyclovir, Valtrex · Antiviral (Herpes)

How it works

12.1 Mechanism of Action Valacyclovir is an antiviral drug active against α-herpes viruses [see Microbiology (12.4) ].

Approved for

papule

vesicle

papule

vesicle

OralTablet

Quick Comparison

AcyclovirValacyclovir

Drug Class

Antiviral (Herpes)

Route

Oral

Half-Life

N/A

FDA Approved

N/A

Pregnancy

N/A

Side Effect Frequency Comparison

Estimated frequency (%) based on clinical trial data

Side Effects

Acyclovir

Fatigue

>10%

Diarrhea

>10%

Nausea

1-10%

Fever

1-10%

Drug Not Working

1-10%

Rash

1-10%

Shortness of Breath

1-10%

Weakness

0.1-1%

Valacyclovir

Fatigue

1-10%

Drug Not Working

1-10%

Nausea

1-10%

Diarrhea

1-10%

Headache

1-10%

Fever

1-10%

Rash

1-10%

Dizziness

1-10%

FDA Warnings

Acyclovir

WARNINGS Acyclovir capsules are intended for oral ingestion only
Renal failure, in some cases resulting in death, has been observed with acyclovir therapy (see ADVERSE REACTIONS: Observed During Clinical Practice and OVERDOSAGE )
Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), which has resulted in death, has occurred in immunocompromised patients receiving acyclovir therapy

Valacyclovir

5 WARNINGS AND PRECAUTIONS Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS): Has occurred in patients with advanced HIV-1 disease and in allogenic bone marrow transplant and renal transplant patients receiving 8 grams per day of valacyclovir tablets in clinical trials
1 Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome (TTP/HUS) TTP/HUS, in some cases resulting in death, has occurred in patients with advanced HIV-1 disease and also in allogeneic bone marrow transplant and renal transplant recipients participating in clinical trials of valacyclovir tablets at doses of 8 grams per day

Clinical Trial Data

No head-to-head clinical studies found for Acyclovir vs Valacyclovir.

Acyclovir vs Valacyclovir: What You Should Know

Key Differences

Safety Considerations

This comparison is for informational purposes only. Always consult a qualified healthcare professional before making medication decisions.