Aciclovir tablets are well established antiviral medicines used to treat cold sores and other herpes infections. When treatment is started early, aciclovir may help shorten a cold sore outbreak and reduce associated discomfort by limiting viral replication. For adults looking for clear, evidence based information about using aciclovir for cold sores, genital herpes or shingles, this guide explains what the medicine does, what benefits you can realistically expect, and how tablet strengths and dosing schedules differ between infections.
You will also find information about the strengths and dosing schedules used for different infections, when treatment should start, when suppressive treatment may be considered, why it is important to follow the prescribed course, and how aciclovir tablets are available through a UK pharmacy. Understanding the correct dose and timing can help you use the medicine safely and set realistic expectations about what aciclovir can and cannot do.
Key things to know
- Aciclovir interferes with the herpes virus's ability to replicate, which may help reduce the severity and duration of an outbreak
- The appropriate dose and treatment schedule depend on the infection being treated, so always follow the regimen prescribed for your specific condition
- 800mg, rather than 400mg, is the higher strength commonly used in treatment regimens for shingles
- Starting treatment as soon as possible after symptoms appear may provide the most benefit, depending on the infection and the prescribed regimen
What Aciclovir Tablets Actually Do
Aciclovir is an antiviral medicine that targets cells infected with herpes viruses. Once inside an infected cell, it is converted into its active form by viral enzymes. It then interferes with the virus's ability to copy its DNA, which limits viral replication.
It is important to understand what this means in practice. Aciclovir can help control an active herpes infection, but it does not cure herpes because the virus remains in the body. Herpes simplex virus can remain inactive in nerve tissue between outbreaks, which means recurrences can happen even after successful treatment. A recurrence does not necessarily mean that previous treatment has failed.
Aciclovir is not an antibiotic and does not treat bacterial infections. It is also not used to treat common viral illnesses such as the common cold.
Other Conditions Aciclovir Treats
As well as cold sores, aciclovir is used to treat genital herpes infections and, at a higher dose, shingles (herpes zoster) and chickenpox. Shingles and chickenpox are caused by varicella zoster virus, which belongs to the same broader herpes virus family as herpes simplex virus but is a different virus.
Each infection has its own recommended dose and treatment schedule. This is why it is important not to assume that the strength or dose used for one condition is suitable for another.
The Genuine Benefit: What the Evidence Shows
When started early in a cold sore outbreak, oral aciclovir may shorten the duration of symptoms. Evidence reviews suggest that treatment can reduce the duration of a cold sore outbreak by around one day compared with no treatment and may also help reduce discomfort.
This is a useful but modest benefit. Aciclovir is not expected to make a cold sore disappear immediately, and claims that it will cut the outbreak duration in half can give unrealistic expectations. The benefit can be more noticeable when treatment is started early, so recognising the first signs of an outbreak can be helpful.
Aciclovir Tablet Strengths: Getting This Right
Aciclovir tablets are available in 200mg, 400mg and 800mg strengths. The strength you need depends on the infection being treated and the dosing schedule prescribed for you.
For cold sores and genital herpes, treatment regimens can include 200mg taken five times a day or 400mg taken three times a day for 5 days, depending on the indication and clinical circumstances. For genital herpes, a 400mg dose taken three times a day is one recognised treatment regimen. The different strengths therefore do not simply mean that one is intended for cold sores and another for a different infection. They can form part of different dosing schedules for the same or different conditions.
For shingles (herpes zoster), 800mg taken five times a day for 7 days is a commonly used treatment regimen in adults. This is a different infection from herpes simplex and requires a different dosing schedule.
Always follow the dose and duration provided by your prescriber or the patient information leaflet for your specific medicine. Do not change the strength or frequency yourself, even if another aciclovir regimen appears similar.
| Strength | Typical use | Typical frequency |
|---|---|---|
| 200mg | Cold sores, genital herpes | 5 times daily, 5 days |
| 400mg | Cold sores, genital herpes (alternative schedule); also used for suppressive therapy | 3 times daily, 5 days (or twice daily for suppression) |
| 800mg | Shingles (herpes zoster) | 5 times daily, 7 days |
Some sources may suggest that 400mg tablets are intended only for certain herpes virus infections and are not suitable for cold sores. This does not match prescribing guidance for aciclovir. A 400mg dose may be prescribed for cold sores, particularly when a three times daily schedule is more convenient than taking 200mg five times daily. If you are prescribed aciclovir three times a day, try to space the doses evenly throughout the day, following the instructions provided by your prescriber or pharmacist.
Both 200mg and 400mg regimens can be used to treat cold sores when prescribed appropriately. One is not simply a higher tier of treatment reserved for more serious infections. The right strength and schedule depend on your individual circumstances and the regimen prescribed for you.
Suppressive Therapy for Frequent Outbreaks
If you experience frequent genital herpes recurrences, aciclovir may sometimes be prescribed as suppressive treatment. This means taking a lower dose regularly rather than only during an active outbreak, with the aim of reducing how often recurrences happen.
Suppressive treatment may be considered when outbreaks are frequent or have a significant effect on your quality of life. The exact threshold can vary, but recurrent episodes occurring six or more times a year may be one reason a prescriber considers this approach.
Suppressive treatment involves taking medicine regularly over a longer period, so it is different from taking a short course when an outbreak starts. If frequent outbreaks are affecting your daily life, speak with your prescriber about whether suppressive treatment could be appropriate for you.
Timing Matters More Than the Specific Strength
Starting treatment as early as possible can be helpful. For cold sores, this may mean taking aciclovir when you first notice the prodromal symptoms, such as tingling, itching or burning, before a visible blister appears. Starting treatment promptly may give you a better chance of reducing the duration of an outbreak.
The specific strength is less important than following the regimen prescribed for your condition. Both 200mg and 400mg regimens are established treatment options for cold sores when used appropriately.
If you regularly experience cold sores, having an appropriate supply available may make it easier to start treatment promptly when symptoms begin. Speak with a pharmacist or prescriber about whether keeping a supply at home is suitable for you.
Completing the Course
Take aciclovir for the full length of time prescribed, even if your symptoms start to improve sooner. This helps you follow the treatment plan provided by your prescriber.
If you miss a dose, take it when you remember unless it is nearly time for your next dose. If your next dose is due soon, skip the missed dose and continue with your usual schedule. Do not take two doses together to make up for a missed dose.
If you are unsure what to do after missing several doses or have accidentally taken more than prescribed, speak with a pharmacist or healthcare professional for advice.
Ready to start treatment? Start your free cold sore consultation and a prescriber will confirm the right strength and schedule for you.
Available Treatments
| Treatment | Price |
|---|---|
| Aciclovir Tablets | From £12.99 |
| Aciclovir 5% Cream | From £8.99 |
| Valaciclovir | From £18.99 |
| Valtrex | From £34.99 |
Prices update live and may change.
Medical Disclaimer
This page provides general information about aciclovir tablets, their benefits, and dosing. It is not a substitute for personalised medical advice, diagnosis, or treatment. The strength, dosing frequency, and course length prescribed for you depend on your individual condition and should be confirmed by a prescriber.
Aciclovir can cause side effects, although not everyone experiences them. Common side effects can include headache, nausea, and dizziness. Serious reactions are uncommon but can occur, particularly in people with kidney problems. Staying well hydrated may be particularly important if you have factors that increase your risk of kidney problems.
If you experience dizziness or other symptoms that could affect your concentration or ability to react, avoid driving or operating machinery until you feel well enough to do so.
If you have questions about your specific treatment, side effects, or dose, speak with your prescriber, pharmacist, or GP.
