200mg
How do aciclovir tablets for cold sores work?
Aciclovir 200mg tablets contain the antiviral medicine aciclovir, which works by stopping the herpes simplex virus that causes cold sores from multiplying. It does this by interfering with the virus's DNA, making it harder for the infection to spread. Although aciclovir can't remove the virus from your body, it can help your immune system bring the outbreak under control more quickly.
The earlier you begin treatment, the more effective aciclovir is likely to be. It's best to start taking your tablets as soon as you notice the first signs of a cold sore, which can include:
- tingling
- itching
- burning
- redness around your lips
Starting treatment before a blister develops may help reduce the severity of your breakout.
Aciclovir tablets are particularly helpful for people who:
- experience frequent, severe or widespread cold sores
- find topical treatments difficult to use
Because the medicine works throughout your body, it targets the virus from within rather than only treating the symptoms on the skin.
If you're unsure whether your symptoms are caused by a cold sore, speak to your GP or pharmacist before starting treatment.
How long do cold sores take to heal with aciclovir?
Without treatment, most cold sores clear up within 7-10 days. Taking aciclovir tablets as soon as symptoms begin can help shorten this healing time and may reduce the severity of your outbreak.
Everyone responds differently to treatment, so the exact time will vary. You may find that your blister doesn't fully develop, or that your pain and discomfort improves sooner than it would without treatment.
To give aciclovir the best chance of working, it's important to complete your prescribed course, even if your symptoms begin to improve after a few days.
Alongside taking your tablets, there are a few simple things you can do to support healing:
- avoid touching or picking at your cold sore
- wash your hands after applying any cold sore treatments
- stay well hydrated
- avoid sharing towels, cutlery or lip products while you have an active cold sore
- consider using a lip balm with SPF to help protect against sun-triggered outbreaks
If your cold sore hasn't started improving after 10 days, or it becomes unusually large, painful or widespread, seek advice from your GP.
How to use aciclovir 200mg tablets
Always take aciclovir exactly as directed by your prescriber or according to the patient information leaflet supplied with your medicine.
For treating cold sores, the usual adult dose is one 200mg tablet five times a day, spaced approximately four hours apart during waking hours. Treatment is usually continued for five days, although your prescriber may recommend a longer course if needed.
- Swallow each tablet whole with a glass of water.
- You can take aciclovir with or without food, although taking it after eating may help if you experience mild stomach discomfort.
- Stay well hydrated while taking aciclovir, particularly if you're older or have reduced kidney function. Drinking plenty of fluids can help support your kidneys while your body processes the medicine.
- Try to take your tablets at evenly spaced intervals throughout the day. Setting reminders on your phone or linking your doses to regular daily activities can help you remember your treatment schedule.
Even if your symptoms begin to improve, continue taking the tablets until you've finished the course unless you've been told otherwise by your healthcare professional. Stopping treatment too early could make it less effective.
What to do if you miss a dose
If you forget to take a dose of aciclovir, take it as soon as you remember unless it's nearly time for your next scheduled dose.
If your next dose is due soon, skip the missed dose and continue taking your tablets as normal.
Do not take two doses together to make up for a forgotten tablet, as this won't improve how well the medicine works and may increase your risk of side effects.
If you regularly forget to take your medicine, setting an alarm or using a medication reminder app may help you stay on track.
Aciclovir 200mg side effects
Like all medicines, aciclovir can cause side effects, although not everyone experiences them. Most people take aciclovir without any problems, and any side effects are usually mild and temporary.
Common side effects include:
- headaches
- feeling sick (nausea)
- diarrhoea
- stomach pain
- dizziness
- feeling tired
- skin rash or increased sensitivity to sunlight
These side effects often improve as your body gets used to the medicine. If they become troublesome or don't go away, speak to your pharmacist or GP.
If you feel dizzy or faint after taking aciclovir tablets, do not drive or use machinery until these symptoms have resolved.
When to seek medical help
Although serious side effects are rare, stop taking aciclovir and seek urgent medical advice if you develop:
- swelling of your face, lips, tongue or throat
- difficulty breathing or wheezing
- a severe skin rash, blistering or peeling skin
- confusion, hallucinations or unusual drowsiness
- difficulty passing urine or significantly reduced urine output
- severe or persistent abdominal pain
You should also seek medical advice if your cold sore symptoms continue to worsen despite treatment, you develop a fever or feel generally unwell, or you experience frequent outbreaks that are becoming more severe, as further assessment may be needed.
When not to use aciclovir 200mg tablets
Aciclovir 200mg tablets aren't suitable for everyone. Before starting treatment, make sure your prescriber knows about any medical conditions you have and any medicines you're taking.
Do not take aciclovir if you're allergic to aciclovir, valaciclovir or any of the other ingredients in the tablets. Signs of an allergic reaction include a rash, swelling of your face or throat, or difficulty breathing. If you experience these symptoms after taking aciclovir, seek urgent medical attention.
Speak to your GP or pharmacist before taking aciclovir if you:
- have kidney problems or reduced kidney function
- have a weakened immune system due to illness or medication
- have previously experienced a reaction to antiviral medicines
- are taking medicines that may affect your kidneys
If you're pregnant, think you may be pregnant or are planning a pregnancy, speak to your healthcare professional before taking aciclovir. They'll help you weigh up the benefits and any potential risks to determine whether it's the right treatment for you.
Aciclovir passes into breast milk in small amounts. If you're breastfeeding, ask your GP, pharmacist or prescriber for advice before taking this medicine.
Always tell your healthcare professional about any prescription medicines, over-the-counter treatments, vitamins or herbal supplements you're taking to help avoid potential interactions.
Storage information
Store aciclovir tablets below 25°C in their original packaging to help protect them from moisture.
Keep the medicine out of the sight and reach of children and don't use it after the expiry date printed on the packaging.
If you have any unused or expired tablets once you've finished your treatment, don't throw them away in your household waste or flush them down the toilet. Instead, return them to your local pharmacy where they can be disposed of safely.
Alternatives to aciclovir tablets for cold sores
Aciclovir tablets are an effective treatment for many people, but they aren't the only option available. The best treatment for you will depend on how often you experience cold sores, how severe your symptoms are and when you start treatment.
Medical treatments
If your symptoms are mild or caught early, a cold sore cream containing aciclovir may help reduce the duration of your outbreak. Creams are applied directly to the affected area and work best when used as soon as you notice tingling or itching.
Some people may be prescribed valaciclovir, another antiviral medicine that's converted into aciclovir once it's absorbed. Because it stays in the body for longer, it can often be taken less frequently than aciclovir, making it a convenient option for some patients.
If you experience frequent or severe cold sores, your GP may recommend a different treatment plan, including longer-term antiviral therapy to help reduce the number of outbreaks.
Non-medical treatments
Although they don't treat the virus itself, non-medicated products can help make cold sores more comfortable while they heal.
Cold sore patches can protect the blister from dirt and bacteria while helping to reduce irritation throughout the day. They're also a discreet option if you're concerned about the appearance of a cold sore.
Many people find it helpful to identify and manage their personal cold sore triggers. Common triggers include illness, emotional stress, fatigue and prolonged exposure to sunlight. While these can't always be avoided, recognising patterns may help you reduce the frequency of future outbreaks.
Which is better, Zovirax or aciclovir?
Zovirax is a branded medicine that contains aciclovir as its active ingredient. For most people, there's no clinical difference between branded Zovirax tablets and generic aciclovir tablets. They work in the same way, treat the same viral infections and contain the same strength of medicine.
The main differences are usually the manufacturer, packaging and price. Generic medicines are often a more affordable option while providing the same treatment benefits.
Frequently asked questions about aciclovir 200mg
Can aciclovir 400mg tablets be used for cold sores?
Aciclovir 400mg tablets may be prescribed for certain viral infections, including cold sores. However, the dose you need depends on the condition being treated and your individual circumstances. At Chemist4U, we only prescribe aciclovir 200mg for cold sores.
How often do I take aciclovir for cold sores?
The usual adult dose for treating a cold sore is 200mg five times a day, approximately every four hours during waking hours, for five days.
Your prescriber may recommend a different treatment schedule depending on your symptoms, medical history or kidney function, so always follow the instructions provided with your medicine.
Sources
- Aciclovir 200mg Tablets – Patient Information Leaflet (PIL). [Accessed 21 July 2026].
- Aciclovir 200mg Tablets – Summary of Product Characteristics (SmPC). EMC. [Accessed 21 July 2026].
- Cold sores. NHS. [Accessed 21 July 2026].
- Aciclovir: About aciclovir. NHS. [Accessed 21 July 2026].
