Aciclovir is an antiviral medication used to treat two common viral infections - varicella-zoster and herpes simplex. Herpes simplex viruses cause cold sores and genital herpes. Aciclovir tablets can be used to treat and prevent recurrent genital herpes outbreaks.
Aciclovir is available as 400mg tablets, with each tablet containing the active ingredient aciclovir. It is cheaper than Zovirax, a branded version of aciclovir, and is equally effective.
30 tablet(s) / 400 mg - £24.95
12 tablet(s) / 400 mg - £19.95
24 tablet(s) / 400 mg - £24.95
36 tablet(s) / 400 mg - £29.95
15 tablet(s) / 400 mg - £19.95
30 tablet(s) / 400 mg - £24.95
45 tablet(s) / 400 mg - £29.95
168 tablet(s) / 400 mg - £49.00
Aciclovir is an antiviral medicine. This means it helps kill and slow down the growth of viruses, such as the herpes simplex virus (HSV) that causes genital herpes.
Similar to genital herpes, cold sores are also caused by HSV infections. So you can apply a cream that contains aciclovir to treat cold sores. You might need aciclovir tablets instead if the infection does not clear, or to prevent it from coming back in future.
A doctor may prescribe you aciclovir tablets to help treat:
- shingles, caused by the herpes zoster virus
- chicken pox, caused by the varicella zoster virus
You should take aciclovir tablets with a glass of water at certain times of the day, depending on your treatment plan.
The usual dose is to swallow 1 aciclovir 400mg tablet 3 times a day with a glass of water, and you should wait 8 hours between each dose. An example of the times you need to take each aciclovir tablet looks like this:
- 7am - first tablet
- 3pm - second tablet
- 11pm - third tablet
You should take aciclovir 400mg tablets for 5 days, or for as long as your doctor tells you to if needed.
If you cannot swallow tablets, you can dissolve an aciclovir tablet in a small amount of water and drink all of the liquid.
Aciclovir is not affected by food, so you can eat before or after you take your tablet.
What should I do if I forget to take it?
If you forget to take 1 of your aciclovir tablets, take it as soon as you remember. But if it’s nearly time for you to take your next tablet, then skip the missed dose so you do not take too much aciclovir at the same time. Do not take 2 aciclovir tablets (a double dose) to make up for a missed dose.
What should I do if I take too much?
If you're worried you've taken more aciclovir than you need, you should contact your doctor straight away. Side effects of too much aciclovir include feeling sick or confused.
Aciclovir works to prevent the herpes virus from growing and invading your body. It stops the virus from multiplying as it cannot make the DNA it needs to make copies of itself and spread. This helps to heal your infection and gives your immune system time to fight the virus.
If you're taking aciclovir to prevent recurrent herpes outbreaks, the way you take it is the same as to treat outbreaks but the dose may be different.
For example, you may need to take 200mg of aciclovir 4 times a day at 6 hourly intervals for 6 to 12 months.
Always take the medication as prescribed by your doctor.
Aciclovir is effective at clearing up your infection within 5 days or preventing an outbreak from happening if you start taking it within a few days of symptoms starting.
You should start to feel better after a few days of taking aciclovir.
Aciclovir can prevent the herpes virus from replicating in your system and helps to reduce the spread and severity of the virus, which is normally dormant (asleep) in your nervous system. At the moment, there is no vaccine for the herpes virus.
Common side effects of aciclovir include:
- stomach pains
Uncommon side effects of aciclovir include:
- itchy rash
- hair loss
You can find out more about the side effects of aciclovir, including rare side effects, by reading the patient information leaflet that comes with your aciclovir tablets.
If you experience any side effects whilst taking aciclovir, get in touch with your doctor as soon as possible. You can also report your side effects to the MHRA yellow card scheme online.
Most people can take aciclovir to treat genital herpes or cold sores. But the amount of aciclovir you can take will depend on how healthy you are and other medicines you might be taking at the same time.
Do not take aciclovir if you:
- are allergic to aciclovir or any of the other ingredients
- are allergic to similar antivirals, like valaciclovir
Speak to your doctor before taking aciclovir if you:
- have or have ever had kidney (renal) problems
- are older than 65 years of age
- are pregnant or trying to get pregnant
- are breastfeeding
If you are not sure whether you can take aciclovir, you can take a genital herpes test or speak to a doctor.
For more information, have a look inside the patient information leaflet.
Some other medications can interact with aciclovir and affect how it works. Tell your doctor if you are taking or have recently taken any other medication, including ones without a prescription.
In particular, tell your doctor if you have taken:
- probenecid for gout
- cimetidine for stomach ulcers
- mycophenolate mofetil after having an organ transplant
Find out more in the patient information leaflet that comes with your aciclovir tablets.
If you do not think aciclovir tablets are right for you, there may be an alternative treatment you can take. Other treatments that do the same thing as aciclovir include:
Speak to your doctor if you’d prefer an alternative treatment to aciclovir and they can give you advice on what to do next.
Zovirax is the same as aciclovir, and they are both available as tablets or cream.
Aciclovir is made by different medicines manufacturers to the same standards as Zovirax, so you can be confident the quality and effectiveness is the same.
Dr Babak Ashrafi Clinical Lead for Service Expansion
Accreditations: BSc, MBBS, MRCGP (2008)
Babak studied medicine at King’s College London and graduated in 2003, having also gained a bachelor’s degree in Physiology during his time there. He completed his general practice (GP) training in East London, where he worked for a number of years as a partner at a large inner-city GP practice. He completed the Royal College of GPs membership exam in 2007.Meet our doctors
Last reviewed: 06 Dec 2021
Genital Herpes, National Health Service  [accessed Nov 2021]
Aciclovir Tablets 400mg, Summary of Product Characteristics [accessed Nov 2021]
Aciclovir Product Information Leaflet [accessed Nov 2021]
Aciclovir, British National Formulary [accessed Nov 2021]
Aciclovir (Zovirax), National Health Service [accessed Nov 2021]
You can treat genital herpes two ways. One treatment option is for when you experience an individual outbreak (acute therapy) and the other is treatment for when you need to avoid regular outbreaks (suppressive). ZAVA offers both types of treatment through a discreet, convenient service.