Help cold sores heal faster with aciclovir

  • Works to treat cold sores
  • Helps sores heal faster, and reduces itching and pain
  • Available from £9.99 + prescription fees and delivery costs

Our prices

Strength Quantity Price Stock
200 mg25 tablets£9.99In Stock
200 mg50 tablets£14.99In Stock
200 mg75 tablets£19.99In Stock
400mg15 tablets£14.99In Stock
400mg30 tablets£19.99In Stock
400mg45 tablets£23.99In Stock
Prices exclude a prescription fee. This treatment requires a quick online consultation,
which a doctor will review to determine if a prescription is appropriate.

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  • Fully registered UK pharmacy


Virginia Chachati

Reviewed by Virginia Chachati MPharm
(2013, University College London)
GPhC Registration number: 2087654

Information last reviewed 25/06/2021


What is aciclovir?

Aciclovir is an antiviral medicine used to treat infections caused by the herpes virus. It is commonly prescribed to treat genital herpes, cold sores, chickenpox and shingles. Aciclovir does not cure viral infections. It helps sores to heal, reduces itching and eases pain. Aciclovir can prevent infections in people who have a weak immune system due to medical conditions or the medicines they take.

Aciclovir for cold sore prevention

The two most common infections caused by the herpes virus are cold sores and genital herpes. While symptoms usually clear up, the virus stays in your skin for the rest of your life. You may experience random outbreaks of cold sores or genital herpes. People who have more than 6 outbreaks in a year can take aciclovir for 6 to 12 months as a preventative, or see a specialist for advice.

How long does it take for aciclovir to work?

Aciclovir does not cure genital herpes or cold sores. Cold sores can take up to 10 days to heal, and aciclovir stops them from spreading or getting worse. 

Aciclovir summary


200mg, 5 times per day

Type of Medicine



Competitively inhibits and inactivates viral DNA processes, preventing replication

Available Size

15, 30, 45 or 168 tablets

Available Strengths


Active Ingredient



From 21p per tablet

Side Effects

Can include nausea, vomiting, diarrhoea, headaches, stomach pains, feeling dizzy, feeling tired, fever, itching, skin rash


Active ingredients

The active ingredient in aciclovir tablets is aciclovir.

Inactive ingredients

The inactive ingredients in aciclovir tablets are colloidal anhydrous silica, magnesium stearate, povidone, sodium starch glycollate, indigo carmine lake (E132), microcrystalline cellulose (E460)

Please Note: Different brands of generic aciclovir may contain different inactive ingredients. Please read the patient information leaflet provided for more details


How to take aciclovir

You should take aciclovir tablets by mouth as prescribed by your doctor. To treat cold sores and genital herpes, take 1 tablet 5 times a day and leave 4 hours between each dose. To prevent cold sores and genital herpes, take 1 tablet 4 times a day and leave 6 hours between each dose for 6 to 12 months.

If you have a weak immune system, take 1 tablet 4 times a day with 6 hours between each dose. If you have a problem with your kidney function, you should take 1 tablet twice a day and leave 12 hours between each dose.

Aciclovir tablets are available in 400 mg tablets from Dr Felix. If you cannot swallow tablets, you can dissolve the tablets in water and then drink the liquid mixture.

Aciclovir dosage

Aciclovir tablets are available as 400 mg tablets from Dr Felix. Your doctor will prescribe the right dose for you and advise you on how to take it.

Side Effects

Aciclovir side effects

When you take aciclovir, you might get side effects. Common side effects (affecting less than 1 in 10 people) include dizziness and headaches, nausea or vomiting, diarrhoea, stomach pain, skin rashes and itching, tiredness, sensitivity to sunlight or artificial lights or a high temperature. 

Uncommon side effects (which occur in less than 1 in 100 people) include pale or red raised patches on the skin, severe itching and hair loss.

Less than 1 in 1000 people who take aciclovir might get the following rare side effects:

  • Increase in bilirubin and liver-related enzymes
  • Increase in blood levels of urea and creatinine
  • Impaired kidney function which, in rare cases, can lead to kidney failure
  • Irregular emergence of circular red patches on the skin of the hands and arms
  • Severe skin rash, which may involve reddening, peeling and swelling of the skin resembling severe burns
  • Flushing, fever, blisters or ulcers, signs of Stevens-Johnson syndrome

Extremely rare side effects, which affect less than 1 in 10,000 people, can include:

  • Hepatitis (inflammation of the liver)
  • Jaundice (yellowing of the skin and whites of the eyes)
  • Anaemia, leukopenia or thrombocytopenia
  • Kidney failure; speak to your doctor immediately if you experience increased bruising, nosebleeds, sore throats, infections, excessive tiredness, breathlessness, abnormal paleness of the skin, or lower back pain
  • Nervous system reactions; speak to your doctor immediately if you experience excessive drowsiness, confusion, hallucination, sleepiness, convulsions (fits), coma, general feeling of discomfort and illness, agitation, involuntary shaking, difficulty controlling movements, or difficulty speaking

Speak to your doctor immediately if you experience signs of anaphylaxis (severe allergic reaction) when taking this medicine. Signs include swelling of the face and lips, tongue or throat, and difficulty breathing or swallowing.


You should not take aciclovir if you are allergic to aciclovir or any of the other ingredients in aciclovir tablets. You should speak to your doctor and take extra care when taking aciclovir if you have nervous system problems or kidney problems. You need to drink plenty of water whilst taking aciclovir, especially if you are elderly or taking doses of higher than 4 g per day. 

Drug interactions

Speak to your doctor if you are taking or have been taking any other medicines including:

  • Cimetidine and probenecid, which may increase the concentration of aciclovir
  • Mycophenolate mofetil, as the blood level of both medicines can increase if taken in combination
  • Ciclosporin, as your doctor may wish to monitor your kidney function
  • Theophylline
  • Zidovudine

Aciclovir and pregnancy

If you are pregnant, breastfeeding or trying for a baby, you should speak to your doctor before using aciclovir tablets. Your doctor might recommend using aciclovir cream instead.

Treatment Options

Aciclovir tablets vs cream

Aciclovir is available as tablets or cream. Aciclovir cream is available over the counter and helps treat cold sores. You should apply aciclovir cream on your cold sore five times per day for few days. Do not put aciclovir cream inside the vagina, eyes or mouth.

Aciclovir tablets are used to treat herpes infections that cannot be treated with aciclovir cream. This includes genital herpes. Aciclovir tablets help prevent frequent outbreaks and reduce the spread of viral infections in those with a weak immune system.

Is there a dispersible aciclovir available?

Yes, dispersible aciclovir is available from Dr Felix. If you cannot swallow aciclovir tablets, they can be dispersed or dissolved in a glass of water. To do this, mix one 400 mg tablet in at least 100 ml of water and swallow all the liquid to get your full dose.

Non-prescription alternatives

For mild cases of herpes infection, aciclovir cream can be bought over the counter without a prescription. Aciclovir cream will help treat most cases of cold sores, but you should speak to your doctor if you get cold sores regularly. You can use aciclovir cream and these tips help to clear up your cold sores:

  • Avoid anything that you know triggers cold sores
  • Eat cool, soft foods
  • Avoid acidic or salty foods
  • Wash your hands regularly with soap and hot water, especially before and after applying any creams
  • Use a high SPF sunscreen lip balm to protect the area
  • Use an antiseptic mouthwash
  • Drink plenty of water
  • If you can, take paracetamol or ibuprofen to ease pain and swelling around the infected area


Am I still contagious whilst taking aciclovir?

Yes, you can still be contagious whilst taking aciclovir. The herpes simplex virus is contagious from the first signs of a new outbreak, right up until the sores have fully healed, even when taking aciclovir. It is important to avoid passing on the virus while you have symptoms. If you have a cold sore you should avoid kissing others, especially babies.

Is aciclovir addictive?

Aciclovir is not an addictive medicine. If you accidentally take more aciclovir than recommended, contact a doctor immediately. Overdosing on this medicine can affect your stomach and intestines, or your nervous system.

Is aciclovir an antibiotic?

Aciclovir is not an antibiotic. Aciclovir is an antiviral and treats infections caused by a virus. Antibiotics are used to treat bacterial infections and cannot be used to treat viral infections.

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