Information only, and pending clinical review. These are prescription-only medicines. This page explains how they relate to each other so a conversation with a prescriber makes more sense — it is not advice to take either, not a recommendation of one over the other, and not an offer to supply anything. Dosing, suitability and choice are clinical decisions made for an individual, and nothing here should be used to start, stop or change a medicine.
Valaciclovir becomes aciclovir inside the body.
This is the part that clears up most of the confusion. Valaciclovir is what pharmacology calls a prodrug — an inactive form that the body converts into the active drug after you swallow it. The active drug it converts into is aciclovir.
So these are not two different approaches to the same problem. They are two ways of delivering the same working molecule. The conversion is more efficient, which means valaciclovir gets more of the active drug into the bloodstream from a given dose — and that is why it does not have to be taken as often.
Famciclovir is a third option that appears in the same conversations and works on similar principles.
What actually differs.
- The older and more established of the two, with a very long track record.
- Generally the cheaper option, and widely available as a generic.
- Typically needs taking more times per day, because it is absorbed less efficiently.
- That frequency is its main practical drawback — more doses means more opportunities to forget one.
- Converts to aciclovir in the body, more efficiently absorbed.
- Typically taken fewer times per day, which some people find considerably easier to keep to.
- Usually costs more than aciclovir, though it is also available as a generic.
- Convenience is the main thing being bought, rather than a different mechanism.
For treating outbreaks, both are regarded as effective options. The choice between them tends to come down to how a particular person will actually take them, what else is going on medically, and cost — which is exactly the kind of judgement that needs someone who knows your situation.
The questions behind the comparison.
Is one stronger than the other?
Not in the way the question implies. They deliver the same active drug, so "stronger" is really a question about how much active drug reaches the bloodstream and how often — which is a dosing question, not a potency ranking.
Is the generic as good as the branded version?
A generic contains the same active medicine and must meet the same regulatory standard. It does the same job. The difference is usually the price on the box, which is often several times higher for the brand name. That is why we lead with generics rather than treating them as the budget option.
Does either reduce the chance of passing it on?
Taken daily as suppression, antiviral treatment is understood to lower the risk of transmission — it does not remove it, and no honest brand will tell you otherwise. There is more on how that works, and on what the evidence does and does not support, in suppression and transmission.
Which one would I be given?
That is a decision for a prescriber who has assessed you, taking in your history, other medicines, kidney function, whether you are or may become pregnant, and how a plan fits into your actual life. A comparison page cannot make it, and should not try.
Can I buy them over the counter?
Aciclovir cream for cold sores is available from pharmacies without a prescription. Tablets for genital herpes are prescription-only in the UK, which means an assessment by a prescriber — whether that is your GP, a sexual health clinic, or an online service.
The right question is not which drug. It is which plan.
Whether you need something to take daily, something kept at home for when an outbreak starts, or nothing at all right now, matters more than which of two closely related molecules is on the box.
This page is educational and is not medical advice, a recommendation, or an offer to supply a medicine. Prescription-only medicines require assessment by a prescriber. Do not start, stop or change any medicine on the basis of this page. If you have questions about a medicine you have been prescribed, speak to your pharmacist, GP or sexual health clinic.
Interval’s care service is not yet open, and we do not supply medicines. This page is written by non-clinicians from the sources listed at the foot of the page, and has not been independently reviewed by a clinician.
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- NHS. Genital herpes. www.nhs.uk
- Patel R et al. British Association of Sexual Health and HIV UK national guideline for the management of anogenital herpes, 2024. Int J STD AIDS. pmc.ncbi.nlm.nih.gov
- Corey L et al. Once-daily valaciclovir to reduce the risk of transmission of genital herpes. N Engl J Med 2004;350:11–20. www.nejm.org
Last checked 10 August 2026. Read our editorial policy for how we source and review these pages.