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Acyclovir

Acyclovir

Acyclovir is an antiviral drug prescribed to treat infections such as chickenpox, genital herpes, shingles and cold sores, which are caused by herpes viruses. It decreases the growth and spread of herpes virus in the body and helps faster healing of sores. Acyclovir eye ointment is used to treat viral eye infections caused by herpes simplex viruses. Acyclovir is available as tablet, topical cream and eye ointment forms. This medicine may also be used to treat other conditions as determined by your doctor.
Category: Anti Virals
Medically Reviewed by – Alfie Thornton, PharmD
Last Updated on 8 July 2026

What is Acyclovir used for?

Acyclovir is an antiviral drug prescribed to treat infections such as chickenpox, genital herpes, shingles and cold sores, which are caused by herpes viruses. It decreases the growth and spread of herpes virus in the body and helps faster healing of sores. Acyclovir eye ointment is used to treat viral eye infections caused by herpes simplex viruses. Acyclovir is available as tablet, topical cream and eye ointment forms. This medicine may also be used to treat other conditions as determined by your doctor.

What are the side effects of Acyclovir?

Like other medicines, Acyclovir can cause some side effects. If they do occur, the side effects of Acyclovir are most likely to be minor and temporary. However, some may be serious and may require the individual to inform the doctor or visit the nearest hospital immediately.
  • Headache – This is one of the most common side effects and usually mild.

  • Nausea or vomiting – Some people may feel slightly sick after taking the medicine.

  • Diarrhoea – You may notice loose stools while on treatment.

  • Dizziness or tiredness – It can make you feel light-headed or fatigued.

  • Skin reactions – Rashes or itching may occur in some individuals.

  • Kidney problems – Rarely, Acyclovir can affect kidney function, especially in those with pre-existing issues.

What is the recommended dosage of Acyclovir?

The recommended dosage of Acyclovir depends on the condition being treated. For cold sores or genital herpes, adults usually take it five times a day, while for shingles, it’s often prescribed every four hours. Always follow your doctor’s instructions carefully and complete the full course, even if symptoms improve before finishing the medication.

What if you miss a dose of Acyclovir?

If your physician has instructed or directed you to use Acyclovir medication in a regular schedule and you have missed a dose of this medicine, use it as soon as you remember. However, if it is almost time for your next dose, then skip the missed dose and go back to your regular dosing schedule. Do not double the doses unless otherwise directed.

What if you overdose on Acyclovir?

Any medication taken in excess can have serious consequences. If you suspect an overdose of Acyclovir, seek medical attention immediately.

What other drugs could interact with Acyclovir?

It may be noted that drugs other than those listed above may also interact with Acyclovir. Usually, drug interactions occur when it is taken with another drug or with food. Before you take a medication for a particular ailment, you should inform the health expert about the intake of any other medications including non-prescription medications, over-the-counter medicines that may increase the effect of Acyclovir, and dietary supplements like vitamins, minerals, and herbal, so that the doctor can warn you of any possible drug interactions. Acyclovir can interact with nonsteroidal anti-inflammatory drugs. Do let your doctor know if you smoke, consume alcohol or caffeinated drinks, or use illegal drugs as these may interfere with the action of your medication. Make sure to inform your doctor of any medical conditions you may have, or any family history of medical problems. Do not start or stop using any medicine without consulting your doctor.

Where can I buy Acyclovir over the counter in UK?

In the UK, Acyclovir tablets are only available with a valid prescription from a doctor or pharmacist. You can, however, buy Acyclovir cream for cold sores over the counter at most local pharmacies, supermarkets, or trusted online chemists. Always check the packaging and consult a pharmacist if you’re unsure which form suits your condition.

Can I buy Acyclovir without a prescription in UK?

In the UK, you can’t buy Acyclovir tablets without a prescription, as they’re classed as a prescription-only medicine. However, Acyclovir cream used for cold sores is available to purchase over the counter from pharmacies or reliable online stores. It’s best to speak with a pharmacist to ensure you choose the right treatment for your needs.

How long does it take for acyclovir to work?

Acyclovir usually begins to work within a few days of starting treatment. Most people notice an improvement in their symptoms, such as reduced pain, itching, or tingling, within two to three days. However, it’s important to complete the full course prescribed by your doctor, even if your symptoms improve sooner.

What are the questions to ask your doctor before taking Acyclovir tablet?

Is it possible for me to use Acyclovir with other drugs? Should certain beverages, foods and other products be avoided when I use Acyclovir? What are the possible drug interactions of Acyclovir? How will Acyclovir work in my body? How should Acyclovir be used? How to reduce the risk of Acyclovir drug interactions and side effects?

Note

The health and medical information provided here is intended to supplement and not substitute for the expertise and judgment of your physician, pharmacists or other health care professional. It should not be understood to indicate that the use of Acyclovir is safe, appropriate or effective for you. Always consult your health care professional before using this, or any other, drug.

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