Verified
I started taking it when the tingling began rather than waiting for blisters. The sore still appeared, but it stayed smaller and healed faster than my usual outbreaks.
3 Feb 2026
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Aciclovir
4 (4 customer reviews)Aciclovir is an oral tablet for herpes-virus infections. It is used for genital herpes, oral herpes and cold sores, shingles, chickenpox, and prevention of some herpes infections in people with reduced immune function.
Description
Each Aciclovir tablet contains the dose stated on the pack — follow the leaflet — of aciclovir. It belongs to the antiviral medicines used against herpes viruses, including Herpes Simplex Virus (HSV) and varicella-zoster virus.
Composition
Each Aciclovir tablet contains the dose stated on the pack — follow the leaflet — of aciclovir. It belongs to the antiviral medicines used against herpes viruses, including Herpes Simplex Virus (HSV) and varicella-zoster virus.
Dosage and usage
Aciclovir on this page is supplied as an oral tablet; the dose is stated on the pack — follow the leaflet. The prescribed schedule depends on whether treatment is intended for a first genital herpes episode, a recurrent outbreak, suppression of frequent recurrences, or another herpes-virus infection.
Take the tablet by mouth with water. Food is not required for absorption, so it may be taken with or without a meal. A clinician may adjust the frequency or duration when kidney function is reduced, during severe infection, or when long-term suppressive treatment is needed.
- Take doses at evenly spaced times where possible.
- Swallow the tablet whole with a full glass of water.
- Keep fluid intake steady during treatment, especially during fever, vomiting, diarrhoea, or hot weather.
- If a dose is missed, take it when remembered unless the next dose is nearly due.
- Do not take two tablets together to compensate for one missed dose.
Put treatment times into a phone reminder rather than relying on memory. Aciclovir works best when blood levels stay reasonably consistent across the day.
How it works
Aciclovir is a synthetic nucleoside analogue. This means its structure resembles one of the building blocks that herpes viruses need to make DNA.
Inside an infected cell, viral enzymes activate aciclovir. The activated medicine is then incorporated into viral DNA, where it stops the DNA chain from extending. Viral replication slows down. Healthy cells are less affected because they do not activate aciclovir as efficiently as HSV-infected cells.
The mechanism explains why Aciclovir works against herpes viruses but does not treat bacterial infections, thrush, or ordinary mouth ulcers. The FDA prescribing information describes aciclovir as a selective inhibitor of herpes-virus DNA polymerase. [2]
Indications
Aciclovir is used for genital herpes, oral herpes and cold sores, shingles, chickenpox, and prevention of herpes infections in some people with reduced immune function. Oral treatment may also be used by specialists for herpes simplex eye infections, which need prompt medical assessment because HSV can affect vision. The World Health Organization includes aciclovir on its Model List of Essential Medicines for viral infections caused by herpes viruses. [1]
Aciclovir tablets for cold sores may be considered when outbreaks are severe, frequent, extensive, or difficult to manage with local treatment alone.
People who have repeated disruptive episodes may be offered suppressive antiviral treatment after an individual clinical assessment.
Comparison
Aciclovir and valaciclovir target the same herpes-virus DNA replication process. Valaciclovir is converted into aciclovir after absorption and usually produces higher aciclovir levels from each dose.
| Treatment | Main practical difference | Typical clinical use |
|---|---|---|
| Aciclovir | Lower oral bioavailability; schedules may require more frequent doses | HSV outbreaks, suppression, shingles, chickenpox |
| Valaciclovir | Better oral bioavailability; often less frequent dosing | HSV outbreaks, suppressive treatment, shingles |
Aciclovir remains a well-established option for genital herpes and recurrent HSV infections. CDC sexually transmitted infection guidance includes both aciclovir and valaciclovir among recommended systemic antiviral approaches for genital herpes management. [4]
Contraindications
Aciclovir is not for you if you have had a previous allergic reaction to aciclovir, valaciclovir, or any component of the tablet.
Extra care is needed in the following situations:
- reduced kidney function or dialysis;
- dehydration from illness, exercise, vomiting, or diarrhoea;
- older age with frailty or a history of confusion;
- neurological disease;
- treatment with medicines that can affect kidney function;
- pregnancy or breastfeeding where antiviral treatment has not been clinically assessed.
Probenecid and cimetidine can increase aciclovir exposure by reducing kidney clearance. Mycophenolate mofetil may also raise levels of both medicines. Anti-inflammatory pain medicines, certain antibiotics, ciclosporin, tacrolimus, and other medicines affecting the kidneys can add to renal stress in susceptible people.
When this is not for you
Aciclovir is not for you if you have had a previous allergic reaction to aciclovir, valaciclovir, or any component of the tablet.
Talk to a clinician before treatment if you have kidney problems, are dehydrated, are older and frail, have a history of confusion or neurological disease, take medicines that affect the kidneys, or are pregnant or breastfeeding.
Side effects
Most people tolerate Aciclovir tablets without major problems. The more common unwanted effects are usually mild and improve as treatment ends.
Possible effects include:
- headache;
- nausea;
- vomiting;
- diarrhoea;
- stomach discomfort;
- dizziness;
- itching or a mild skin rash;
- tiredness.
Kidney-related reactions are uncommon with oral treatment at usual doses, yet the risk rises with dehydration, older age, high doses, or impaired kidney function. Confusion, agitation, hallucinations, tremor, or unusual sleepiness need urgent assessment, especially in people with kidney disease.
Stop taking Aciclovir and seek urgent medical care for facial swelling, wheezing, tightness of the throat, widespread hives, collapse, or other signs of anaphylaxis. Serious skin reactions are also rare but require urgent attention. UK product information lists gastrointestinal symptoms, headache, skin reactions, and rare neurological or renal reactions among reported adverse effects. [3]
Nausea is often easier to manage when the tablet is taken after a small meal. Drinking water with each dose also supports kidney clearance of aciclovir.
Common mistakes
- Starting treatment only after a cold sore has crusted over, rather than acting at the tingling stage.
- Missing doses because the schedule is inconvenient.
- Taking an extra tablet after a forgotten dose.
- Drinking too little during a fever or stomach bug.
- Assuming that healed skin means HSV can no longer recur.
- Continuing to touch a facial lesion, then touching the eyes or genital area.
- Sharing tablets intended for another person’s diagnosis or dose plan.
For recurrent genital herpes, keep a brief record of outbreak dates, triggers, and symptom duration. It gives a prescriber useful information when deciding whether episodic or suppressive treatment fits best.
What doctors say
In clinical practice, doctors often find that expectations shape satisfaction with antiviral treatment. Aciclovir can reduce the severity and duration of an outbreak, yet it does not eradicate latent HSV from nerve cells or make future recurrences impossible.
For recurrent genital herpes, the key decision is often episodic versus suppressive treatment. Episodic treatment is taken at the first signs of a flare. Suppressive treatment is considered when outbreaks are frequent, prolonged, painful, or emotionally disruptive.
Doctors also pay close attention to kidney function. A standard schedule may need adjustment in renal impairment, and symptoms such as new confusion or reduced urine output should never be dismissed as routine treatment effects.
Frequently asked questions
Can Aciclovir be taken with alcohol?
Alcohol does not directly block the antiviral action of Aciclovir. NHS medicines guidance reviewed in 2023 states that alcohol can be consumed while taking aciclovir. Heavy alcohol intake may worsen dehydration, nausea, poor sleep, and headache, all of which can make an outbreak feel harder to manage. Keeping hydrated is more useful than drinking heavily while unwell.
How quickly does Aciclovir start working?
Aciclovir starts interfering with viral replication after it is absorbed and activated in infected cells. The FDA prescribing information, revised in 2021, describes its selective activity against herpes-virus DNA replication. Symptom relief is usually gradual rather than immediate, and lesions may still need several days to heal. Starting treatment during tingling or early blister formation can improve the practical result.
Can Aciclovir prevent genital herpes outbreaks?
Suppressive treatment can reduce the frequency of recurrent genital herpes for people with repeated episodes. The CDC’s 2021 sexually transmitted infection guidance recognises daily suppressive antiviral therapy as an option for recurrent HSV-2 genital herpes. It does not eliminate HSV from the body, and breakthrough episodes can still occur. A regular suppressive schedule should be tailored to the person’s recurrence history and renal function.
Is Aciclovir suitable during pregnancy?
Aciclovir may be used during pregnancy when there is a clear clinical reason, such as genital herpes management. UKTIS guidance published in 2024 reports that available data do not identify aciclovir as a major teratogen. Treatment decisions near delivery are more urgent because active genital herpes can affect neonatal care. Obstetric teams may use antivirals to reduce the risk of a recurrence at birth.
Can Aciclovir treat shingles or chickenpox?
Aciclovir has activity against varicella-zoster virus, the virus responsible for chickenpox and shingles. The WHO Model List of Essential Medicines published in 2023 includes aciclovir for herpes-virus infections. For shingles, prompt treatment matters most when rash, pain, or blisters have recently started. A rash near the eye, facial weakness, severe headache, or widespread blisters needs urgent assessment.
What should I do if I develop eye symptoms during a herpes outbreak?
A painful red eye, light sensitivity, blurred vision, eyelid swelling, or a sensation of grit can indicate herpes simplex eye involvement. NHS guidance updated in 2023 advises urgent assessment for suspected eye infection. Oral Aciclovir may form part of specialist treatment, yet eye infections need examination because corneal involvement can threaten vision. Avoid contact lenses until the eye has been assessed and symptoms have resolved.
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Comparison
Compare all medications for AntiviralAciclovir: Reviews and Experiences
Verified
The first day gave me a mild headache, which settled after I drank more water and took the tablet after food. It helped me feel more in control of outbreaks.
22 Jan 2026
Verified
The pain did not disappear straight away, and the first few days were still difficult. By the end of the course the lesions were healing and the burning had eased.
18 Feb 2026
Verified
I missed two doses during a busy weekend and noticed the episode lasted longer than expected. Setting reminders made the next course much easier to follow.
28 Jan 2026
Sources
- World Health Organization (2023). WHO Model List of Essential Medicines: 23rd List.
- U.S. Food and Drug Administration (2021). Zovirax (acyclovir) Prescribing Information.
- electronic Medicines Compendium (2024). Aciclovir 400 mg Tablets: Summary of Product Characteristics.
- Centers for Disease Control and Prevention (2021). Sexually Transmitted Infections Treatment Guidelines, 2021.
