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Acyclovir (Between cheek and gum)

Acyclovir (ay-SYE-kloe-vir)

Treats cold sores. This medicine is an antiviral.

Brand Name(s):


There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. Do not use it if you had an allergic reaction to acyclovir or milk protein concentrate.

How to Use This Medicine:


  • Your doctor will tell you how much medicine to use. Do not use more than directed.
  • Use this medicine within 1 hour after you have the first symptom of a cold sore and before a cold sore begins. Apply the tablet on the same side of your mouth that has the cold sore symptoms.
  • To use: Peel back the cover of the blister pack to remove the tablet. Use a clean, dry finger to place the tablet on your gum. Place it above the tooth that is next to your front tooth. Press on your upper lip lightly for 30 seconds to make sure the tablet sticks.
  • The tablet will dissolve gradually throughout the day. Do not crush, chew, suck on, or swallow the tablet.
  • Do not chew gum, touch or press the tablet, wear upper dentures, or brush your teeth after you place the tablet.
  • You may eat and drink while the tablet is in place. Drink more liquids if your mouth becomes dry.
  • If the tablet does not stick or falls off within the first 6 hours, use the same tablet and place it back onto your gum. If it still does not stick, replace it with a new tablet.
  • If you swallow the tablet within the first 6 hours of applying it, drink a glass of water and place a new tablet on your gum.
  • Do not apply a new tablet if the tablet falls out or if you swallow it after it has been in place 6 hours or longer.
  • Read and follow the patient instructions that come with this medicine. Talk to your doctor or pharmacist if you have any questions.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

Warnings While Using This Medicine:

  • Tell your doctor if you are pregnant or breastfeeding, or if you have a weak immune system.
  • Call your doctor if your symptoms do not improve or if they get worse.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing

If you notice these less serious side effects, talk with your doctor:

  • Pain or irritation of the gums

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 5/1/2020

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites.

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