Get emergency medical help if you have signs of an allergic reaction to acyclovir: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
easy bruising or bleeding, purple or red pinpoint spots under your skin;
changes in behavior;
confusion, hallucinations; or
signs of a kidney problem - little or no urinating; painful or difficult urination; swelling in your feet or ankles; feeling tired or short of breath.
Common acyclovir side effects may include:
mild skin pain;
rash, itching;
nausea, vomiting, diarrhea;
headache; or
mouth pain while using an acyclovir buccal tablet.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Acyclovir side effects (more detail)
