Both treatments work. The question is which fits your lifestyle better. Here's how aciclovir and valaciclovir compare on dosing, convenience, cost, and effectiveness.
If you've been prescribed treatment for genital herpes, there's a good chance you're familiar with aciclovir and valaciclovir. Both are effective antivirals, available from Pharmica, and do essentially the same job. So what's the difference, and which one is right for you?
This guide compares aciclovir vs valaciclovir side-by-side, covering how they work, how you take them, and what to consider when choosing between the two for episodic and suppressive treatment of genital herpes.
How do Aciclovir and Valaciclovir Treat Genital Herpes?
Both aciclovir and valaciclovir are antiviral medications. They work by blocking the herpes simplex virus (HSV) from copying itself, which helps shorten outbreaks and reduce their severity.
Valaciclovir is actually a prodrug of aciclovir, which means your body converts it into aciclovir after you swallow it. Once they're in your system, valaciclovir works the same way as aciclovir as it is turned into the same active ingredient.
The main difference is how well they're absorbed. Valaciclovir has a significantly higher bioavailability than aciclovir (around 54% compared to roughly 15-20%), which is why it can achieve similar antiviral levels in the blood with fewer doses per day.
Aciclovir vs Valaciclovir at a Glance
| Feature |
Aciclovir |
Valaciclovir |
| Standard dose (episodic treatment) |
400mg, five times daily |
500mg, twice daily |
| Treatment duration (episodic) |
5 days |
3-5 days |
| Suppressive dose |
400mg, twice daily |
500mg, once daily |
| Bioavailability |
15-20% |
~54% |
| Doses per day (episodic) |
5 |
2 |
| Doses per day (suppressive) |
2 |
1 |
| Available from Pharmica |
Yes |
Yes |
Dosing and Convenience
This is where the practical difference between aciclovir and valaciclovir becomes clear.
For an episodic outbreak, the standard aciclovir dosage for genital herpes is 400mg taken five times a day for five days. That means spacing doses roughly every three to four hours during waking hours. For most people with busy lives, that's a lot to keep track of.
Valaciclovir simplifies things. The standard dosage is 500mg twice daily for three to five days. Two doses a day is much easier to fit around work, travel, or anything else going on in your life.
When it comes to compliance, fewer doses means less likelihood of you missing a dose. Research consistently shows that simpler dosing schedules lead to better adherence, and better adherence means the medication can work as intended.
If you know you're likely to forget or not be able to take a mid-afternoon dose, valaciclovir's twice daily timing makes it much easier to stick to the schedule.
How Effective is Aciclovir Compared to Valaciclovir?
In terms of clinical outcomes, the two treatments perform the same. A randomised controlled trial conducted by the International Valaciclovir HSV Study Group in 1997 compared aciclovir and valaciclovir for episodic treatment of recurrent genital herpes in 739 patients and found no significant difference in healing time, duration of viral shedding, or pain duration between the two.1
A separate trial published by Fife and colleagues in the same year compared the two medications in 643 adults with first-episode genital herpes and reached the same conclusion - no significant difference in healing time, pain duration, or viral shedding.2
Whether you're treating a first episode or a recurrence, the clinical evidence shows you're not sacrificing effectiveness by choosing one over the other. The key difference is convenience, not potency.
If you want a deeper understanding of how these treatments fit into a broader management plan, Pharmica's guide to treating and suppressing herpes covers the options in more detail.
Suppressive Therapy for Recurring Outbreaks
If you're getting frequent outbreaks (typically six or more per year), you may be recommended suppressive therapy. This involves taking antiviral medication daily to reduce the frequency and severity of recurrences, rather than treating each outbreak as it happens.
Both aciclovir and valaciclovir are used for suppressive therapy, but the dosing schedules differ:
- Aciclovir: 400mg twice daily
- Valaciclovir: 500mg once daily
For long-term daily treatment, the convenience of a once-daily dose can make a real difference to consistency. Suppressive therapy is typically reviewed after 12 months to assess whether it's still needed, though many people continue it for longer.
Suppressive therapy also reduces the risk of passing the virus to a sexual partner. A landmark trial published in the New England Journal of Medicine in 2004 followed 1,484 HSV-2 discordant couples (where one person has HSV-2 and the other does not) for eight months and found that daily valaciclovir reduced the rate of HSV-2 transmission by 48%.3 If reducing transmission risk is part of your motivation, this is a conversation worth having with your prescriber.
Side Effects of Aciclovir and Valaciclovir
Because valaciclovir converts to aciclovir in the body, the side effect profiles of the two medications are very similar. Both are generally well tolerated.
The most commonly reported side effects include:
- headache
- nausea
- stomach pain or diarrhoea
- dizziness
These tend to be mild and settle on their own. Serious side effects are rare but can include confusion, kidney problems (particularly if you're not drinking enough water), and allergic reactions. If you experience anything unusual, speak to our pharmacy team or your GP.
Staying well hydrated while taking either medication helps your kidneys process it and reduces the risk of side effects. This is especially relevant if you're on higher doses of either medication.
Which Treatment Should You Choose?
Neither aciclovir nor valaciclovir is clinically superior. The decision comes down to your priorities, lifestyle, and routine.
Choose aciclovir if:
- cost is a factor (aciclovir is typically the cheaper option vs valaciclovir)
- you don't mind a more frequent dosing schedule
- you've used it before and it's worked well for you
Choose valaciclovir if:
- you want fewer doses per day for easier compliance
- you're starting suppressive therapy and prefer once-daily dosing
- you've struggled to stick to a five-times-daily schedule in the past
If you're unsure, Pharmica's prescribers can help you decide when you place your order. You can also read more about managing the condition in Pharmica's guide to genital herpes symptoms, causes and treatments or browse expert answers to common questions about genital herpes.
Frequently Asked Questions
Can you switch between aciclovir and valaciclovir?
Yes, you can. Since valaciclovir converts into aciclovir in the body, switching between them is straightforward. Many people start with one and move to the other based on convenience or cost. Your prescriber can adjust your treatment if your current option isn't working for your routine.
Is valaciclovir stronger than aciclovir?
No. Valaciclovir isn't more potent. It has higher bioavailability, meaning your body absorbs more of it per dose, but the active antiviral compound is identical. Clinical trials show equivalent results for both treatments in healing time and symptom relief.
How quickly do aciclovir and valaciclovir work for genital herpes?
Both treatments work fastest when started at the first sign of an outbreak, ideally during the 'tingling' or prodromal stage. Most people notice symptoms beginning to improve within two to three days. Starting treatment early shortens the duration of the episode and can reduce its severity.
Can you buy aciclovir or valaciclovir over the counter?
Neither is available over the counter for genital herpes in the UK. Both require a prescription, which Pharmica can issue through its online consultation service. Aciclovir cream for cold sores is available over the counter, but the tablet form for genital herpes needs to be prescribed to you.
Does suppressive therapy reduce the risk of passing herpes to a partner?
Yes. Daily antiviral therapy has been shown to reduce the risk of transmitting HSV-2 to a partner. A large clinical trial demonstrated a 48% reduction in transmission risk with daily valaciclovir use.3 Using condoms alongside suppressive therapy reduces the risk further.
Can you take aciclovir or valaciclovir during pregnancy?
Aciclovir has a longer safety record in pregnancy and is generally the preferred antiviral if treatment is needed during pregnancy or close to delivery. Your GP or midwife will make the decision based on your individual circumstances. Don't stop or start antiviral treatment during pregnancy without medical advice.
References
- Bodsworth NJ, Crooks RJ, Borelli S, et al. Valaciclovir versus aciclovir in patient initiated treatment of recurrent genital herpes: a randomised, double blind clinical trial. International Valaciclovir HSV Study Group. Genitourinary Medicine. 1997;73(2):110-116. doi: 10.1136/sti.73.2.110
- Fife KH, Barbarash RA, Rudolph T, Degregorio B, Roth R. Valaciclovir versus acyclovir in the treatment of first-episode genital herpes infection. Results of an international, multicenter, double-blind, randomized clinical trial. The Valaciclovir International Herpes Simplex Virus Study Group. Sexually Transmitted Diseases. 1997;24(8):481-486. doi: 10.1097/00007435-199709000-00007
- Corey L, Wald A, Patel R, et al. Once-daily valacyclovir to reduce the risk of transmission of genital herpes. New England Journal of Medicine. 2004;350(1):11-20. doi: 10.1056/NEJMoa035144
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.
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