Sexual Health · Medication Guide
Acyclovir in Thailand
What acyclovir is, how well it works against herpes and shingles, its side effects, and how men in Bangkok get it legally. It controls outbreaks and holds recurrences down, but it does not cure the virus. Reviewed by a licensed physician at a MOPH-registered men's health clinic.
- Start early, within 24–72 hours
- Oral prescription · cold-sore cream over the counter
/)
Medically reviewed by Dr. Noppon Arunkajohnsak (Win)
Menscape Clinic
Last reviewed
11 July 2026
1982
First selective antiviral
the original herpes medicine, still standard
70–80%
Fewer recurrences
on daily suppression, frequent outbreaks
72 h
Window to treat shingles
start within 72 hours of the rash
1–2 days
Faster healing
when episodic treatment starts early
Key takeaways
Acyclovir is an antiviral for herpes infections: cold sores, genital herpes, shingles and chickenpox. It controls outbreaks; it does not remove the virus.
Suppression, not cure: herpes stays dormant in nerve cells for life. Daily acyclovir cuts recurrences by 70–80% in frequent sufferers and lowers the chance of passing it on.
In Thailand, oral acyclovir (400 mg and 800 mg) is a prescription drug; the 5% cold-sore cream is pharmacist-dispensed. Both should come from a licensed source, not a grey-market seller.
A doctor decides the right form, dose and course, and checks kidneys and complications. Acyclovir works best when started within 24–72 hours of the first symptoms.
01
What acyclovir is & how it works
Acyclovir is an antiviral medicine used to treat infections caused by the herpes family of viruses: cold sores (herpes labialis), genital herpes (HSV-1 and HSV-2), shingles and chickenpox (varicella-zoster). It was the first drug of its kind and is still a standard treatment worldwide.
It is a prodrug that only switches on inside infected cells. Herpes viruses make an enzyme, thymidine kinase, that activates acyclovir; the activated drug then blocks the viral enzyme that copies viral DNA, so the virus cannot multiply. Because activation depends on the virus, healthy cells are largely left alone, which is why acyclovir is well tolerated.
Acyclovir controls the infection; it does not clear it. After an outbreak the virus retreats into nerve cells and stays there for life. Taken as a short course it shortens outbreaks, and taken daily it holds recurrences down and reduces the risk of passing herpes to a partner. Whether you need short episodic courses or daily suppressive treatment is a decision for the doctor.
The virus infects a cell
Herpes simplex or varicella-zoster enters skin or nerve cells and begins copying its DNA.
The virus activates the drug
A viral enzyme (thymidine kinase) converts acyclovir into its active form, only inside infected cells.¹
DNA copying is blocked
Activated acyclovir jams the viral DNA polymerase, stopping the virus from replicating.¹
The outbreak settles
Lesions heal faster and viral shedding drops; the virus goes dormant in nerve cells until next time.
02
Getting acyclovir in Thailand
Thai FDA status
Acyclovir is registered with the Thai FDA. Oral tablets (400 mg and 800 mg) are prescription medicines, while the 5% cream for cold sores is available from a pharmacist without a prescription. Registered generics are sold in Thailand under brands such as Zovirax.²
Where it's legal to get
Oral acyclovir must be prescribed by a doctor or dispensed by a licensed pharmacist. A teleconsultation with licensed pharmacy delivery is legal in Thailand, so you can be assessed and treated quickly at the first sign of an outbreak.³
For expats & visitors
No Thai residency is required. If you already take suppressive acyclovir abroad, bring your history and a doctor can continue it. Herpes is common and care here is routine, private and non-judgmental.
Thai FDA warning. Buying prescription antivirals from unlicensed online sellers is illegal and risky; counterfeit and substandard products are common. Self-treating shingles near the eye, or an outbreak in pregnancy or a weakened immune system, can be dangerous; see a doctor first.⁴
03
Does it work? The evidence
Acyclovir is one of the most established antivirals in medicine, approved in the 1980s and studied for four decades. For genital herpes, starting an episodic course early shortens the outbreak and speeds healing, while daily suppressive therapy reduces recurrences by 70–80% in people with frequent outbreaks and lowers viral shedding between episodes.⁵ ⁶
For shingles, starting acyclovir within 72 hours of the rash reduces pain and speeds healing. What acyclovir cannot do is remove the virus: it works while you take it, and herpes can reactivate later. That is why the doctor matches the plan, episodic or suppressive, to how often and how severely you get outbreaks.
70–80%
Fewer recurrences
daily suppression, in frequent sufferers
72 h
Shingles treatment window
start within 72 hours of the rash
Figures from the CDC STI Treatment Guidelines and product labelling. Individual results vary; acyclovir controls herpes but does not cure it.
04
Side effects & who shouldn't take it
Common side effects
Oral acyclovir is usually well tolerated. The most common effects are nausea, headache and diarrhoea. The 5% cream can cause mild burning, stinging or dryness where it is applied, and rarely contact dermatitis.
Serious but rare
High doses, dehydration or existing kidney disease can strain the kidneys, and very high or IV doses can rarely cause confusion, tremor or hallucinations, mostly in older or renally-impaired patients. Drinking enough water lowers the risk. Get urgent care for any severe allergic reaction.
Not suitable for / use with care
Tell your doctor if you have kidney problems, are dehydrated, or are pregnant or breastfeeding, as the dose may need adjusting. Acyclovir has a long safety record and is used in pregnancy when needed, but only a doctor should decide.
Interactions & warnings
Combining acyclovir with other drugs that affect the kidneys (for example probenecid, or certain painkillers) can raise its levels. Keep well hydrated, finish the full course, and start treatment as early as possible for the best effect.
05
Alternatives & combinations
Oral · fewer doses
Valacyclovir
A prodrug of acyclovir that the body absorbs better, so it can be taken fewer times a day. A doctor may prefer it for convenience or to help reduce transmission to a partner.
Oral · alternative
Famciclovir
Another oral antiviral in the same family, used for genital herpes and shingles. An option when acyclovir is not suitable or not tolerated.
Topical · cold sores
Acyclovir 5% cream
Caught early, the topical cream can be used on its own for cold sores. For frequent or severe outbreaks a doctor may add or switch to oral treatment.
06
How prescription works at Menscape
/)
Talk to a doctor at the first sign of an outbreak.
Message us on WhatsApp or LINE
A few minutes on your phone: your symptoms, history and any current medicines. It is private and PDPA-protected. Start at the first sign of an outbreak.
Doctor consultation
A licensed Thai physician reviews your case by video call or in clinic at Asoke, confirms whether it is herpes or shingles, and checks for anything that needs closer care.
Prescription, if suitable
If appropriate, you receive a prescription for the right form and dose, episodic or suppressive, dispensed by a licensed pharmacy for pickup or delivery. The cold-sore cream can be supplied without a prescription.
Follow-up
For daily suppressive treatment the doctor reviews how you are doing and adjusts the plan; kidney function is checked when long-term or high-dose treatment is needed.
The doctor decides. Starting a conversation is not a commitment and does not guarantee a prescription. If acyclovir is not right for you, your doctor will explain why and discuss alternatives.
Medically reviewed by
Dr. Noppon Arunkajohnsak (Win)
Menscape Clinic, Bangkok
“Herpes is far more common than people think, and it's very manageable. What matters is starting treatment early and choosing the right plan: a short course for the occasional outbreak, or daily suppression when they keep coming back.”
- Reviewed
- 11 July 2026
- Next review
- January 2027
- Editorial standard
- Each guide is checked against the Thai FDA label and the primary literature, then reviewed by a licensed physician.
07
Frequently asked questions
Can I buy acyclovir over the counter in Thailand?
The 5% cream for cold sores is available from a pharmacist without a prescription. Oral acyclovir tablets (400 mg and 800 mg) are prescription-only, so they must be prescribed by a doctor or dispensed by a licensed pharmacist. Anything sold without that oversight risks being counterfeit.
Does acyclovir cure herpes?
No. Acyclovir controls the virus but cannot remove it. Herpes stays dormant in nerve cells for life; the medicine shortens outbreaks and, taken daily, holds them down and lowers the risk of passing it on.
How quickly should I start it?
As early as possible. Episodic treatment for cold sores or genital herpes works best when started at the first tingle or within 24 hours. For shingles, start within 72 hours of the rash appearing.
What's the difference between episodic and suppressive treatment?
Episodic means a short course taken at the start of each outbreak to speed healing. Suppressive means a lower daily dose taken continuously to prevent outbreaks, usually chosen when they are frequent or you want to reduce transmission. Your doctor decides which fits you.
Can I reduce the chance of passing herpes to my partner?
Daily suppressive therapy lowers viral shedding and reduces the risk of transmission, though it does not remove it. Combined with condoms and avoiding sex during outbreaks, it meaningfully cuts the risk. A doctor can set this up.
Is acyclovir hard on the kidneys?
For most people at normal oral doses, no. The main precaution is staying well hydrated, especially at higher doses. If you have any kidney problems the dose is adjusted, so tell your doctor about your kidney history.
Can I take acyclovir if I'm pregnant or planning a family?
Acyclovir has a long track record and is used in pregnancy when the benefit outweighs the risk, but this is a decision only a doctor should make. Tell your doctor if you are pregnant, planning to be, or breastfeeding.
What's the difference between acyclovir and valacyclovir?
Valacyclovir is a prodrug of acyclovir that the body absorbs better, so it can be taken fewer times a day. Acyclovir is the long-established standard; a doctor may suggest valacyclovir for fewer daily doses or to help reduce transmission.
08
References
1. Elion GB. Acyclovir: discovery, mechanism of action, and selectivity. Journal of Medical Virology. 1993.
2. Thai Food and Drug Administration. Drug registration database, ndi.fda.moph.go.th. Accessed July 2026.
3. Pharmacy Council of Thailand, Notification No. 56/2563 on telepharmacy standards.
4. U.S. FDA. Zovirax® (acyclovir) prescribing information. Accessed July 2026.
5. Centers for Disease Control and Prevention. Sexually Transmitted Infections Treatment Guidelines: Genital Herpes. 2021.
6. Wald A, et al. Suppression of subclinical shedding of herpes simplex virus type 2 with acyclovir. Annals of Internal Medicine. 1996;124(1):8-15.
7. World Health Organization. WHO Model List of Essential Medicines (aciclovir). 2023.
This guide is educational information, not medical advice. Oral acyclovir is a prescription medicine that must be prescribed and monitored by a licensed physician, and herpes or shingles should be diagnosed by a doctor.
This guide is part of the Menscape sexual-health library
Explore the condition hubThink it might be herpes or shingles? Ask a doctor, not a forum.
/)