What is Valaciclovir?

Valaciclovir is an antiviral medicine used to treat cold sores (herpes labialis) caused by the herpes simplex virus (HSV-1). It stops the virus from multiplying, helping to reduce symptoms such as tingling, pain and itching and to shorten the time to healing.

Although valaciclovir is also licensed for other herpes infections, this page and our service provide it only for the short-course treatment of cold sores.

What is Valaciclovir Used For?

Valaciclovir is prescribed to treat cold sores in adults and adolescents aged 12 years and over.

How Valaciclovir Works

After you swallow the tablets, valaciclovir is converted to aciclovir, which then changes into its active triphosphate form. This active compound blocks the viral DNA polymerase enzyme, preventing the herpes virus from copying its genetic material and spreading.

Taking the medicine at the first sign of a cold sore helps limit the outbreak and shorten healing time.

Cold Sores: Symptoms, Treatment, and Healing Tips

Symptoms: Tingling, itching or burning around the lip is usually followed by small fluid-filled blisters. Cold sores are contagious from the first tingle until the skin has completely healed, typically within about 10 days.

Treatment Options: Cold sores often heal on their own, but oral antivirals such as valaciclovir can reduce discomfort and speed recovery when started early. Pain-relieving gels or creams and sun-protective lip balms can also help.

Healing Tips: Protect lips with a balm containing SPF 15 or higher, keep hands clean, avoid kissing or sharing utensils while sores are present, eat soft foods if lips are sore, and drink plenty of fluids.

Can you buy Valaciclovir over the counter?

No. In the UK, valaciclovir is a prescription-only medicine (POM). You need a consultation with a registered prescriber to ensure it is safe and appropriate before it can be supplied.

Alternative Medications

If valaciclovir is not suitable, other prescription antivirals can also treat cold sores:

Aciclovir – works the same way but requires more frequent dosing each day

How to take Valaciclovir

For cold sores only (short-course treatment):

Adults and adolescents (≥12 years): Take 2,000 mg twice in one day, 12 hours apart.

Start as soon as you notice the first signs such as tingling, burning or itching.

Swallow tablets whole with a full glass of water. Drink plenty of fluids throughout the day to protect kidney function.

If you miss a dose on that same day, take it as soon as you remember. If the day has passed, do not double the dose—seek advice from your prescriber.

Active ingredient: Valaciclovir hydrochloride.

Inactive ingredients may vary by manufacturer but typically include: microcrystalline cellulose, crospovidone (Type A), povidone (K-90), magnesium stearate, and a film coating of hypromellose, macrogol, polysorbate 80, titanium dioxide (E171) and indigo carmine aluminium lake (E132).

Always check the patient information leaflet (PIL) in your pack for the full ingredient list — especially if you have allergies or sensitivities.

Most people tolerate valaciclovir well. Common side effects include headache, nausea, abdominal pain, diarrhoea, dizziness and tiredness.

Seek urgent medical help by calling 999 if you notice:

• Signs of an allergic reaction (difficulty breathing, swelling of the face, lips, tongue or throat)
• Confusion, hallucinations or unusual agitation
• Very little or painful urination, swelling of the feet or ankles, or shortness of breath (possible kidney effects)
• Staying well hydrated lowers the risk of kidney problems.