What are the most common side effects of acyclovir?
Common side effects of acyclovir (including oral tablets/solution and topical forms) tend to be mild and may include:
- Nausea, vomiting, diarrhea, or stomach upset
- Headache
- Dizziness or feeling tired
- Skin reactions where it’s applied (for topical acyclovir), such as burning, itching, or redness
- Mild rash
Do side effects differ by how you take acyclovir?
Yes. Side effects often depend on the form and route:
- Oral acyclovir: gastrointestinal upset and headache are commonly reported.
- Topical acyclovir: local irritation at the application site (burning, itching, redness) is more likely than whole-body side effects.
- IV acyclovir (usually given in a hospital setting): patients can have additional risks related to the infusion, but those are typically discussed separately from “common” outpatient side effects.
When should someone stop and get urgent help?
Seek urgent medical care if you develop signs of a serious reaction, including:
- Trouble breathing, swelling of the face or throat, or widespread hives
- Severe rash with blistering or peeling skin
- Signs of kidney problems (for example, much less urine than usual, severe back/flank pain, or marked confusion), especially in people with kidney disease or those receiving higher doses
Who is more likely to experience side effects?
Side effects can be more likely in people with:
- Kidney problems (acyclovir is cleared by the kidneys)
- Dehydration
- Older age
- Higher dosing or more frequent dosing
If you share the form you mean (tablet, cream/ointment, or IV) and your dose, I can narrow the side effects to what’s most typical for that exact use.