Sildenafil in Thailand: Generic Viagra Explained, Including Dosage and Side Effects

Clinically reviewed by Dr. Ponlawat Pitsuwan, Physician, Doctor Bangkok. Last reviewed: October 2026

I see this at least a few times a week. A man comes in, usually an expat or someone visiting Bangkok, who has been buying sildenafil from a pharmacy near his hotel or condo. No prescription, no questions asked. Sometimes it has worked fine. Sometimes it has not. Occasionally, he is in my clinic because something worried him.

The medication is widely available here, but available is not the same as safe without context. The drug itself is well-understood and effective for most men with erectile dysfunction. The problems I see come from self-dosing at 100mg without any assessment, mixing it with things that make it dangerous, or buying a product that is not what it claims to be.

What Sildenafil Is and What It Does

Sildenafil helps increase blood flow to the penis during sexual arousal, making an erection easier to achieve and maintain. The key word is during arousal. It does not cause an erection on its own. You still need sexual stimulation. This surprises more men than you might expect on the first dose.

It starts working within 30 to 60 minutes for most men and stays active for around four to six hours. A heavy meal before taking it can slow this down significantly, and I will come back to that.

Sildenafil, Sidegra, and Generic Viagra in Thailand

These three terms confuse a lot of people, so here is the short version. Viagra is the original brand made by Pfizer. It costs significantly more than generics. Sidegra is a brand-name generic produced by Thailand’s Government Pharmaceutical Organization, a government body with genuine quality controls. It contains the same active ingredient at the same doses. Clinically, the two are equivalent.

Then there are other generics sold under various names, often without clear origin labelling. That is where my confidence drops.

At Doctor Bangkok, we prescribe and dispense Sidegra after a short consultation. It is the product I am most comfortable recommending here because I know where it comes from and what is in it.

Sildenafil Dosage in Thailand: How to Take It Correctly

The recommended starting dose is 50mg, taken about one hour before sex, once in any 24-hour period. That is what clinical guidelines say. That is not what Bangkok pharmacies typically dispense. Most hand out 100mg without asking a single question.

Dose determines both how well it works and how hard the side effects hit. Some men do very well on 25mg, particularly older patients or anyone with liver or kidney issues. Starting at 100mg without knowing your baseline is not good medicine.

Take it on an empty stomach or after a light meal. A fatty meal can delay absorption by more than an hour, which is why some men take it and assume it has not worked. Keep alcohol minimal. One drink is probably fine. Three is not.

Sildenafil Side Effects: What to Expect

The common side effects are headache, flushing, nasal congestion, and a feeling of indigestion. Most men get one or two of these at 100mg. At 50mg, they tend to be milder and pass within a few hours.

Some men notice a blue-tinged visual effect or sensitivity to light. This is temporary and fades as the drug clears your system.

Three things need urgent attention. A prolonged erection lasting more than four hours, known as priapism, is a medical emergency. It is rare but can cause permanent damage without prompt treatment. Sudden vision loss in one or both eyes is also an emergency. So is chest pain during or after taking sildenafil. If any of these happen, go to an emergency room. Do not wait.

You can read more about managing sildenafil side effects and what to watch for on our sexual health page.

Who Should Not Take Sildenafil: Contraindications and Drug Interactions

This is the section that matters most if you are self-medicating.

The most dangerous combination is sildenafil with nitrates. Nitrates include heart medications like nitroglycerin and recreational drugs called poppers, which are common in Bangkok nightlife. Combining sildenafil with any nitrate can cause a sudden, severe drop in blood pressure. This can be fatal. There is no safe way to combine them.

Alpha-blockers, used for prostate problems or high blood pressure, can also cause a blood pressure drop when taken with sildenafil. The interaction is manageable with careful dosing, but it requires a doctor’s input.

Some medications slow how your body processes sildenafil, meaning the drug builds up to higher levels than intended. Certain antifungal medications and some HIV treatments fall into this category. If you take either, your dose needs adjustment.

A quick medical history review at a clinic like Doctor Bangkok is not a formality. It is the step that catches the things that could genuinely hurt you. If you want to understand more about erectile dysfunction treatment options in Bangkok, our sexual health page covers what we assess and why.

Why Buying Sildenafil Without a Prescription in Bangkok Carries Real Risk

Sildenafil is legally a prescription-only medication in Thailand. In practice, many pharmacies in tourist areas sell it without one. I am not going to pretend otherwise. But three real risks come with that.

First, no one checks your other medications. The nitrate interaction described above does not come with a warning label at the counter. Second, dosing is defaulted to 100mg regardless of your age, weight, or health. Third, counterfeit sildenafil is a genuine problem in Bangkok. Thai FDA enforcement operations have repeatedly seized fake erectile dysfunction products, some containing no active ingredient, some containing unknown substances at incorrect doses.

If you are buying loose tablets from an unmarked source, you do not know what you are taking. The cost of a proper consultation in Bangkok is low. The risk of skipping it is not.

Getting a Sildenafil Prescription at Doctor Bangkok

A consultation for sildenafil at Doctor Bangkok takes around 15 minutes. I ask about your medical history, your current medications, your blood pressure, and whether you have had any heart problems. I am not there to judge. I am there to make sure the medication is safe for you and prescribe a dose that makes sense.

Most men are surprised by how straightforward it is. Some have been putting it off for months, either from embarrassment or because they assumed it would be complicated. It is not. If everything checks out, you can leave with a prescription the same day. We can also dispense Sidegra directly from the clinic.

If you have not had a general health check recently, this is a good time to look at blood pressure and basic metabolic markers. Erectile dysfunction can sometimes be an early indicator of cardiovascular issues, and catching that early is worth doing.

Sildenafil vs Tadalafil: Which One Suits You Better?

Sildenafil works for four to six hours and needs to be timed around sex. Tadalafil, the active ingredient in Cialis, works for up to 36 hours and can also be taken as a low daily dose. For men who want less scheduling around the medication, tadalafil often suits them better.

Side effect profiles are similar. Tadalafil more commonly causes back pain and muscle aches. Sildenafil more commonly causes the visual effects and flushing. The contraindications are the same: both are absolutely contraindicated with nitrates.

Which is better depends on the person. I usually let patients try both, starting at appropriate doses, and we go from there. Both are available at Doctor Bangkok following a consultation. You can find more detail on our men’s sexual health consultations page.

DR Ponlawat

Dr. Ponlawat Pitsuwan is a physician at Doctor Bangkok, a private clinic in central Bangkok. He sees expats, residents, and medical tourists for general medicine, wellness consultations, and IV therapy. His focus is straightforward, evidence-based care delivered in plain language.