Is one more effective?

Neither label claims superiority. They describe their own approved schedules, and the substance reaching the infection is the same in both cases.

Can either prevent transmission?

One of the labels addresses transmission for a specific indication under specific conditions. It is worth reading in full on that medicine's page rather than summarised here.

Comparison

Valaciclovir and aciclovir, compared from both labels

One becomes the other inside the body. The difference is how efficiently it gets there, and that single fact explains the dosing, the price and why both are still prescribed.

From the approved label

The two labels, side by side

	Valtrex	Aciclovir tablets
Approved uses	ValtrexVALTREX is a deoxynucleoside analogue DNA polymerase inhibitor indicated for: Adult Patients	Aciclovir tabletsHerpes Zoster Infections: Acyclovir tablets, USP are indicated for the acute treatment of herpes zoster (shingles).
Forms and strengths	ValtrexTablets: 1-gram: Each blue, film‑coated, capsule‑shaped tablet, with a partial scorebar on both sides, printed with "VALTREX 1 gram" contains 1.112 grams of valacyclovir hydrochloride equivalent to 1...; Tablets: 1 gram (partially scored)	Aciclovir tabletsAcyclovir tablets USP, 800 mg containing 800 mg of acyclovir USP are blue, oval, biconvex tablets debossed with 'J' on one side and '50' on the other side.
How it is taken	ValtrexVALTREX may be given without regard to meals. Valacyclovir oral suspension (25 mg/mL or 50 mg/mL) may be prepared extemporaneously from 500-mg VALTREX tablets for use in pediatric patients for whom a solid dosage form is not appropriate. Adult Dosage	Aciclovir tabletsAcute Treatment of Herpes Zoster: 800 mg every 4 hours orally, 5 times daily for 7 to 10 days.
Must not be used when	ValtrexVALTREX is contraindicated in patients who have had a demonstrated clinically significant hypersensitivity reaction [e.g., anaphylaxis, severe cutaneous adverse reactions (SCARs)] to valacyclovir, acyclovir, or any component of the formulation.; Hypersensitivity to valacyclovir (e.g., anaphylaxis), acyclovir, or any component of the formulation.	Aciclovir tabletsAcyclovir tablets are contraindicated in patients who have had a demonstrated clinically significant hypersensitivity reaction [e.g., anaphylaxis, severe cutaneous adverse reactions (SCARs)] to acyclovir, valacyclovir, or any component of the formulation (see WARNINGS and ADVERSE REACTIONS).
Common side effects	Valtrexmost common adverse reactions reported in at least 1 indication by greater than 10% of adult subjects treated with VALTREX and observed more frequently with VALTREX compared with placebo are headache, nausea, and abdominal pain.	Aciclovir tabletsHerpes Simplex: Short-Term Administration: The most frequent adverse events reported during clinical trials of treatment of genital herpes with acyclovir tablets 200 mg administered orally 5 times daily every 4 hours for 10 days were nausea and/or vomiting in 8 of 298 patient treatments (2.7%). Nausea and/or vomiting occurred in 2 of 287 (0.7%) patients who received placebo.
Boxed warning	Valtrex-	Aciclovir tablets-
Label holder	ValtrexREMEDYREPACK INC.	Aciclovir tabletsCamber Pharmaceuticals, Inc.
Label version	Valtrex16 July 2026	Aciclovir tablets2 February 2026

Built at page render time from the same imported label data as the medicine pages, so it cannot drift away from them.

Written by us

One is a delivery form of the other

Valaciclovir is converted into aciclovir after absorption. Because it is absorbed more efficiently, fewer doses per day achieve what aciclovir needs more doses to achieve, which is the whole of the practical difference.

Both labels cover genital herpes and both describe episodic and suppressive schedules. The indications lists differ in their other entries, and the table above shows where.

Cost against convenience

Aciclovir is cheaper. Valaciclovir requires fewer tablets a day. For a short course during an outbreak the difference is minor; for continuous suppressive use over months it is the reason most prescriptions go one way rather than the other.

Questions

Is one more effective?: Neither label claims superiority. They describe their own approved schedules, and the substance reaching the infection is the same in both cases.
Can either prevent transmission?: One of the labels addresses transmission for a specific indication under specific conditions. It is worth reading in full on that medicine's page rather than summarised here.

Sources

VALTREX: prescribing informationDailyMed, US National Library of Medicine. Label version 16 July 2026
Acyclovir: prescribing informationDailyMed, US National Library of Medicine. Label version 2 February 2026