Reduce the severity and frequency of cold sores with Aciclovir

Aciclovir is an antiviral medication that’s commonly prescribed to reduce the severity of herpes infections, including genital herpes, cold sores, chickenpox and shingles. Aciclovir helps sores heal faster and reduces itching and pain.

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Strength Quantity Price Stock
200mg25 tablets£9.99In Stock
200mg50 tablets£14.99In Stock
200mg75 tablets£19.99In 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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What is Aciclovir?

Aciclovir is an antiviral medication used to treat infections caused by certain types of viruses. It is most commonly prescribed to treat conditions caused by the herpes virus, including genital herpes, cold sores, chickenpox and shingles. Aciclovir does not cure these infections, but reduces the severity and frequency of outbreaks, helps sores to heal, and reduces itching and pain.

Aciclovir is also used to prevent herpes simplex infections in patients whose immune system is compromised for a period of time and is less able to fight infections unaided. 

Aciclovir for prevention

The two most common infections caused by herpes simplex are cold sores and genital herpes. While symptoms usually clear up, the virus stays in your skin for the rest of your life and you may experience recurrent outbreaks of cold sores or genital herpes. Patients who experience more than 6 outbreaks in a year may wish to take Aciclovir over a period of 6-12 months as a preventative. If you continue to suffer from outbreaks during this period, you may be referred to a specialist. 

How long does it take for Aciclovir to work?

Aciclovir does not cure genital herpes and cold sores, but stops the virus from spreading, allowing symptoms to heal. Cold sores can take up to 10 days to heal, and are prevented from spreading or worsening by taking Aciclovir. 


Active ingredients

The active ingredient of this medication is aciclovir PhEur.

Inactive ingredients

Aciclovir 200mg tablets also contain colloidal anhydrous silica, magnesium stearate, povidone, sodium starch glycollate, indigo carmine lake (E132), microcrystalline cellulose (E460)

Please Note: Inactive ingredients may be different for different brands of generic medication.


How to take Aciclovir

Aciclovir 200mg tablets should be taken orally as directed by your doctor. For treatment of herpes simplex infections (cold sores and genital herpes), 1 tablet should be taken 5 times a day at 4 hourly intervals for 5 days. For prevention of herpes simplex infections (cold sores and genital herpes), take 1 tablet 4 times a day at 6 hourly intervals for 6-12 months.

Where a patient’s immune system is not working properly, 1 tablet should be taken 4 times a day at 6 hourly intervals for the period at which the patient is at risk. If a patient is suffering from severely impaired kidney function, they should take 1 tablet twice a day at 12 hourly intervals.

Children under 2 years of age should take half the adult dose according to the criterion outlined above.

For treatment of Varicella infection (chicken pox) in children under 2 years, 1 200mg tablet should be taken 4 times a day. For children between 2 and 5 years of age, 400mg should be taken 4 times a day. For children of 6 years and over, the dose is 800mg 4 times a day. Aciclovir tablets are available in 400mg and 800mg doses. If the patient is struggling to swallow the tablets, they can be dispersed in water.

Aciclovir dosage

Aciclovir tablets can be bought in 200mg, 400mg and 800mg doses. Your doctor will prescribe the right dose for you and advise you on how to take it.

Side Effects

Aciclovir side effects

Taking Aciclovir can occasionally result in 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, 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 users may experience 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, affecting less than 1 in 10,000 patients, can include:

  • Hepatitis (inflammation of the liver)
  • Jaundice (yellowing of the skin and whites of the eyes)
  • Anaemia, leucopenia or thrombocytopenia
  • Kidney failure. Inform 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. Inform 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 difficults speking.

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

Drug interactions

You should consult your doctor if you are taking or have been taking any other medications, particularly the following:

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


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 abnormalities or kidney problems.It is vital to stay hydrated and drink plenty of water whilst taking Aciclovir, especially if you are elderly or taking doses of higher than 4g per day. 

Aciclovir and pregnancy

Aciclovir is thought to be safe to use during pregnancy, although there is very little information to support a yes or no answer. If pregnant or breastfeeding, you can speak to your doctor about any possible health risks to you or your baby. This medication does pass into breast milk but is unlikely to harm a nursing infant. It may well be that a topical form of Aciclovir, which has a much lower rate of absorption into the bloodstream, will be sufficient treatment for you.

Treatment Options

Aciclovir tablets vs cream

Aciclovir is available both as an oral medication and as a topical cream. Aciclovir cream is available over the counter and is usually sufficient treatment for cold sores if applied 3 -5 times per day at regular intervals. It is for external use only and should ne be applied inside the vagina, eyes or mouth.

Aciclovir tablets are used to treat more severe cases of herpes infection, including genital herpes, for preventing frequent outbreaks and for preventing spread of infection in those with a weakened immune system.

Non-prescription alternatives

For mild cases of herpes infection, Aciclovir cream can be bought over the counter without a prescription. The cream suffices as treatment for most cases of cold sores, but it is important to consult your doctor if you experience cold sores on a regular basis. Alongside using Aciclovir cream, the following measures will help to clear up your cold sores:

  • Avoid anything that you known triggers cold sores
  • Eat cool, soft foods
  • Wash your hands regularly with soap and hot water, especially before and after applying cream
  • Use sunblock lip balm to protect the area
  • Use an antiseptic mouthwash
  • Drink plenty of fluids
  • Take paracetamol or ibuprofen to ease pain and swelling around the infected area. 

Is there a dispersible Aciclovir available?

If you struggle to swallow Aciclovir tablets, they can be dispersed in a glass of water. One 200mg tablet should be dispersed in at least 50ml of water and swallowed. This may be a more appropriate when administering the medication to small children.


Will Aciclovir affect a drug test?

There is some evidence that taking Aciclovir can interfere in a drug tests, including urine tests. However, this depends on the type of test and what you are being tested for. Speak to your doctor for more information if you are worried about this issue.

Is Aciclovir an antibiotic?

Aciclovir is an antiviral, a drug administered to treat infections caused by a virus. Antibiotics are used to treat bacterial infections and cannot be used for treating viral infections.

Is Aciclovir addictive?

Aciclovir is not considered to be an addictive medication. If you accidentally take more than you recommended dose of Aciclovir, contact a doctor immediately. Overdosing on this medication can affect your stomach and intestines or your nervous system.

Am I still 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 are suffering from cold sores, avoid kissing others, especially babies. 

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