What side effects can acyclovir tablets (pills) cause?
Acyclovir tablets can cause a range of side effects. Commonly reported effects include stomach and nervous system symptoms, such as nausea and headache. Some people also report dizziness or diarrhea.
Less common but more serious reactions can include allergic symptoms (for example, rash, swelling, or trouble breathing) and kidney problems. Kidney risk is especially important in people who are older, dehydrated, or already have kidney disease.
What side effects should you watch for right away?
Get urgent medical help if you have signs of a serious allergy, including:
- Swelling of the face, lips, tongue, or throat
- Hives or widespread rash
- Trouble breathing or wheezing
Also seek prompt care for possible kidney issues, especially if you notice:
- Much less urine than usual
- Severe back/flank pain
- Extreme fatigue, confusion, or sudden worsening weakness
Can acyclovir cause kidney problems?
Yes. Acyclovir can affect kidney function, particularly when doses are high or the person is dehydrated. This is one reason healthcare providers often stress good hydration and dose adjustments for people with reduced kidney function.
Do side effects differ by dose or duration?
They can. Higher doses and longer treatment increase the chance of side effects, including kidney-related problems. If you’re taking it for recurrent outbreaks versus a longer course, side effects may feel different because exposure time and dose can change.
Who is more likely to get side effects?
Risk is higher in people who:
- Are older
- Have kidney disease or reduced kidney function
- Are dehydrated
- Take other medicines that affect the kidneys
- Have a history of medication allergies
What can you do to reduce side effects?
- Stay well hydrated unless your clinician has told you to restrict fluids.
- Follow the dosing schedule exactly as prescribed.
- Contact your clinician if you develop persistent vomiting, severe headache, confusion, decreased urination, or a new rash.
When should you call your prescriber?
Call your prescriber promptly if you have:
- A rash that’s new or getting worse
- Persistent nausea, vomiting, or dizziness that interferes with daily activity
- Any signs of kidney trouble (especially reduced urination)
- Side effects that start after beginning the medication or rapidly worsen
Are there alternatives if pills cause problems?
If acyclovir tablets are not tolerated, clinicians may consider alternatives within the same antiviral class or adjust the dose. The right option depends on what you’re treating (cold sores, genital herpes, shingles, or chickenpox) and your kidney function.
If you tell me what condition you’re taking acyclovir for (and your dose in mg and how many times per day), I can narrow down the side effects that are most relevant to your situation.