Erectile Dysfunction · Medication Guide
Sildenafil in Thailand
What sildenafil is, how well it works for erectile dysfunction, its side effects, and how men in Bangkok get it legally and safely. Reviewed by a licensed physician at a MOPH-registered men's health clinic.
- Works in 30–60 minutes
- Thai FDA registered · prescription only
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Medically reviewed by Dr. Noppon Arunkajohnsak (Win)
Menscape Clinic
Last reviewed
11 July 2026
30–60
Minutes to onset
taken before planned activity
~4 h
Half-life in the body
the effective window for most men
1998
First oral ED medicine
the year the US FDA approved it
69%
Successful attempts
versus 22% on placebo, landmark trial
Key takeaways
Sildenafil is an oral prescription medicine for erectile dysfunction (ED), and the first PDE-5 inhibitor, in clinical use since 1998.
In the landmark trial, 69% of intercourse attempts succeeded on sildenafil versus 22% on placebo. It only works alongside sexual stimulation, and does nothing without it.
In Thailand it is a specially controlled drug (ยาควบคุมพิเศษ): prescription only. Counterfeit ED pills are widespread in tourist areas and online, and are unsafe.
It must never be combined with nitrate heart medicines. A doctor checks your heart health and current medications before prescribing.
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What sildenafil is & how it works
Sildenafil is an oral prescription medicine used to treat erectile dysfunction, the inability to get or keep an erection firm enough for sex. ED is common and usually has a physical cause, from blood-flow and vascular problems to diabetes, so it is treated as a medical condition, not a lifestyle matter.
It works on the plumbing of an erection. When a man is aroused, nerves in the penis release nitric oxide, which raises a signalling molecule called cGMP that relaxes the blood vessels and lets erectile tissue fill with blood. An enzyme, PDE-5, breaks cGMP down again. Sildenafil is a PDE-5 inhibitor: it slows that breakdown, so an erection is easier to achieve and sustain.
One point matters for safety and for expectations: sildenafil does not create arousal or desire. It only restores the physical mechanism, and only when sexual stimulation is present. Whether it is right for you depends on your heart health, other medications and the cause of your ED, which is what the doctor's assessment is for.
Stimulation releases nitric oxide
Sexual arousal signals nerves in the penis to release nitric oxide.
cGMP relaxes the vessels
Nitric oxide raises cGMP, which relaxes smooth muscle so blood fills the erectile tissue.
PDE-5 ends the erection
The enzyme PDE-5 breaks cGMP down, which is why an erection can be hard to sustain.¹
Sildenafil blocks PDE-5
It slows that breakdown so an erection lasts, but only while you are aroused.¹
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Getting sildenafil in Thailand
Thai FDA status
Registered with the Thai FDA and classified as a specially controlled drug (ยาควบคุมพิเศษ), the strictest prescription tier. Originally marketed under brands such as Viagra, it is now also available as registered generics, in standard tablets and an oral thin-film that dissolves on the tongue.³
Where it's legal to get
Only on a doctor's prescription, dispensed by a licensed pharmacy or clinic. Unlike some countries, no pharmacist can sell it to you without one. Expats and visitors need no Thai residency; bring your medical history and a list of current medicines, especially any heart drugs.
The counterfeit problem
ED pills are among the most-faked medicines in Thailand. Versions sold in bars, night markets, tourist areas and unlicensed websites often contain the wrong dose, no active drug, or undeclared ingredients. Nobody is accountable for what you receive.⁵
Thai FDA warning. The regulator (อย.) repeatedly warns against buying sexual-health medicines from unlicensed sellers. A legitimate supply always starts with a prescription from a licensed doctor.⁵
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Does it work? The evidence
Sildenafil is one of the most-studied medicines in men's health. In the pivotal randomised, placebo-controlled trials (Goldstein et al., New England Journal of Medicine, 1998), 69% of attempts at intercourse were successful on sildenafil, compared with 22% on placebo, and about 82% of men reported improved erections.²
It works across many causes of ED, including harder-to-treat groups such as men with diabetes, though the success rate there is lower.⁴ Two things to keep in mind: it does not work for every man, and it does nothing without sexual stimulation. Onset is usually 30–60 minutes, and a heavy, fatty meal can delay it.
69%
Sildenafil
of intercourse attempts successful
22%
Placebo
same measure, no active drug
Randomised, placebo-controlled trials in men with erectile dysfunction of mixed cause (Goldstein et al., NEJM 1998). Individual results vary.
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Side effects & who shouldn't take it
Common side effects
Headache (about 16%), facial flushing (about 10%), indigestion (about 7%), nasal congestion and a temporary blue-tinged or blurred vision are the most reported. It can also lower blood pressure, felt as dizziness. Most effects are mild and pass as the dose wears off.¹
Serious but rare
Seek urgent care for an erection lasting over 4 hours (priapism), which can damage tissue. Sudden loss of vision or hearing has been reported rarely; stop the medicine and get help if either occurs.¹
Not suitable for
Anyone taking nitrate heart medicines, and men with recent heart attack or stroke, unstable angina, very low blood pressure, severe heart failure, or serious liver or kidney disease. A doctor must review your cardiovascular health first.
Interactions to flag
Nitrates are an absolute no. Alpha-blockers and other blood-pressure drugs, some antifungals and HIV medicines, and grapefruit can all affect it. Do not combine it with other ED pills, and tell your doctor everything you take.
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Alternatives & combinations
Oral · longer-acting
Tadalafil
A related PDE-5 inhibitor that lasts far longer (up to around 36 hours) and can be taken as needed or in a low daily dose. A doctor may suggest it if you want a longer window or dose daily.
Oral · alternative
Vardenafil or avanafil
Other PDE-5 inhibitors in the same family, with slightly different onset and side-effect profiles. Useful options if sildenafil does not suit you well.
Root cause · essential
Treating the underlying cause
ED can be an early warning of heart disease, diabetes or hormonal issues. A proper work-up, plus changes to blood pressure, weight and smoking, often improves erections and your wider health.
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How prescription works at Menscape
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Book your consultation today.
Message us on WhatsApp or LINE
Five minutes on your phone: symptoms, health history and current medications, especially any heart drugs. It is free and PDPA-protected.
Doctor consultation
A licensed Thai physician reviews your case by video call or in clinic at Asoke, checks your cardiovascular health and decides whether medication is safe for you.
Prescription, if suitable
If the doctor approves, you receive a prescription and can discuss the formulation, tablet or thin-film. It is dispensed by a licensed pharmacy for pickup or delivery.
Follow-up & monitoring
A check-in on how it worked, any side effects and the dose, plus a look at any underlying causes worth treating alongside it.
The doctor decides. Starting a conversation is not a commitment and does not guarantee a prescription. If sildenafil is not right for you, for example if you take nitrates, the doctor will say so and discuss safer options.
Medically reviewed by
Dr. Noppon Arunkajohnsak (Win)
Menscape Clinic, Bangkok
“Erectile dysfunction is common and treatable, and it can be an early sign of heart or metabolic disease. The safest thing a man can do is get a proper assessment before taking anything, rather than buy a pill from a stranger.”
- 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.
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Frequently asked questions
Can I buy sildenafil over the counter in Thailand?
No. It is a specially controlled drug (ยาควบคุมพิเศษ), the strictest prescription tier, so it must be prescribed by a doctor and dispensed by a licensed pharmacy. Anything sold without a prescription is illegal and a counterfeit risk.
Is the cheap ED medication sold in tourist areas and online real?
Often not. ED pills are among the most-faked medicines in Thailand, and versions from bars, markets and unlicensed sites may contain the wrong dose, no active ingredient, or undeclared substances. There is no way to verify them and no one accountable if something goes wrong.
How quickly does it work, and how long does it last?
It usually takes effect within 30–60 minutes and has an effective window of around 4 hours. A heavy, fatty meal beforehand can slow the onset.
Do I need to be sexually aroused for it to work?
Yes. Sildenafil does not create desire or cause an erection on its own. It restores the physical mechanism, but only when sexual stimulation is present.
I have a heart condition or take heart medication. Is it safe?
It depends, and this is exactly what the doctor checks. Sildenafil must never be taken with nitrate heart medicines, and it needs caution with several heart conditions and blood-pressure drugs. Tell the doctor your full medical history before starting.
What is the difference between sildenafil and tadalafil?
Both are PDE-5 inhibitors that work the same way. Sildenafil acts for about 4 hours and is taken as needed; tadalafil lasts much longer (up to around 36 hours) and can be taken daily. A doctor helps you choose based on how you want to use it.
What are the most common side effects?
Headache, facial flushing, indigestion, a stuffy nose and temporary changes in vision are the most reported. Most are mild and fade as the dose wears off. Seek urgent care for an erection lasting over 4 hours.
Can I do this by teleconsultation, or continue a prescription from abroad?
Many cases can be handled by teleconsultation, which is legal in Thailand, though the doctor may ask you to come to the clinic at Asoke for an in-person check. If you already take sildenafil abroad, a local doctor can review it and provide a prescription.
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References
1. U.S. FDA. Viagra® (sildenafil citrate) prescribing information. Pfizer. Accessed July 2026.
2. Goldstein I, et al. Oral sildenafil in the treatment of erectile dysfunction. N Engl J Med. 1998;338(20):1397-1404.
3. Thai Food and Drug Administration — drug registration database, ndi.fda.moph.go.th. Accessed July 2026.
4. Rendell MS, et al. Sildenafil for treatment of erectile dysfunction in men with diabetes. JAMA. 1999;281(5):421-426.
5. Thai FDA (อย.) consumer warnings on counterfeit and unlicensed sexual-health medicines, oryor.com.
6. European Medicines Agency. Sildenafil — product information and assessment report. Accessed July 2026.
7. Pharmacy Council of Thailand, Notification No. 56/2563 on telepharmacy standards.
This guide is educational information, not medical advice. Sildenafil is a prescription medicine that must be prescribed and monitored by a licensed physician, who should first assess your cardiovascular health.
This guide is part of the Menscape ED library
Explore the condition hubStruggling with erections? Ask a doctor, not a street vendor.
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