Sildenafil: Complete Guide for Filipino Men
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Sildenafil is a prescription medicine for erectile dysfunction (ED), sold as Viagra (made by Pfizer) and as generic sildenafil. It is listed for up to about 4 hours and is not sold over the counter in the Philippines. Online, NowExpress lists generic sildenafil 50mg x 4 tablets at around ₱750 and Viagra 50mg x 4 tablets at around ₱4,400 (October 2026).
Start your free assessment or see Viagra (sildenafil) and Generic Sildenafil on NowExpress. Prices can change; the product page shows the current price.
How does sildenafil work?
To understand sildenafil, you need to understand what happens during a normal erection.
When a man is sexually aroused, the brain sends signals that trigger the release of nitric oxide (NO) in the penile tissue. Nitric oxide activates an enzyme called guanylate cyclase, which increases levels of a molecule called cyclic GMP (cGMP). cGMP relaxes the smooth muscle in the blood vessels of the penis, allowing blood to flow in and produce an erection.
Here is where the problem starts for men with ED: an enzyme called PDE5 (phosphodiesterase type 5) breaks down cGMP. When PDE5 is too active or cGMP levels are too low, the blood vessels cannot relax enough to allow a full erection.
Sildenafil blocks PDE5. By inhibiting this enzyme, sildenafil allows cGMP to accumulate, which means the blood vessels stay relaxed longer and blood flow to the penis increases during arousal.
The critical point: Sildenafil does not create erections on its own. Sexual stimulation is still required to trigger the nitric oxide cascade. The drug amplifies your body's natural response. It does not override it.
How long does sildenafil take to work, and how long does it last?
Most men notice effects within 30 to 60 minutes, and the label lists the effect for up to about 4 hours.
Absorption: After you take a tablet orally, sildenafil is absorbed through the gastrointestinal tract. Peak plasma concentration (the point when the drug reaches maximum levels in your blood) occurs about 30 to 120 minutes after taking the dose, with a median of about 60 minutes.
Onset of action: Most men notice the effects within 30 to 60 minutes. Some men respond faster, particularly on an empty stomach.
Duration of effect: Up to about 4 hours. This does not mean a 4-hour erection. Sexual stimulation is still needed.
Half-life: The label half-life of sildenafil is about 4 hours. Trace amounts may remain in the body for up to about 24 hours, but they are not meant to have an effect.
Food interaction: This matters. High-fat meals can delay absorption. If you eat a heavy meal before taking sildenafil, it may take longer to work. Ask your doctor about timing with meals.
What strengths does sildenafil come in?
Sildenafil comes in three standard strengths: 25mg, 50mg and 100mg. Your doctor decides which one is right for you.
25mg is the lowest strength, 50mg the middle one, and 100mg the highest on the label. NowExpress carries 50mg and 100mg. Which strength fits you is your doctor's call, based on your age, your health and the other medicines you take.
Your doctor decides the dose. It depends on your health, other medicines and how you respond, which is one reason a doctor review matters.
Who can take sildenafil?
Sildenafil is approved for adult men (18 years and older) with erectile dysfunction. ED can have many underlying causes: cardiovascular disease, diabetes, hormonal imbalances, neurological conditions, psychological factors, medication side effects, or a combination.
Clinical studies have looked at sildenafil in men with a range of ED causes, including:
- Men with diabetes-related ED
- Men who have undergone prostatectomy (prostate removal surgery)
- Men with spinal cord injuries
- Men with psychogenic (anxiety-related) ED
- Men with mild, moderate, and severe ED as measured by the IIEF (International Index of Erectile Function)
However, sildenafil is not suitable for everyone. There are absolute contraindications where taking sildenafil can be dangerous or fatal.
Who should not take sildenafil?
Absolute contraindications (do NOT take sildenafil if you):
- Take nitrate medications. This includes nitroglycerin (sublingual tablets, patches, sprays), isosorbide mononitrate, isosorbide dinitrate, and recreational nitrites ("poppers" such as amyl nitrite or butyl nitrite). Combining sildenafil with nitrates can cause a severe, potentially fatal drop in blood pressure. This is the most important safety rule.
- Take riociguat (Adempas), a medication for pulmonary hypertension. The combination can cause dangerous hypotension.
- Have been advised by a doctor to avoid sexual activity due to a cardiovascular condition. The physical exertion of sex can be risky for certain heart conditions, regardless of medication.
Conditions requiring medical evaluation before use:
- Heart disease, heart failure, unstable angina, recent heart attack or stroke (within the past 6 months)
- Very low blood pressure (below 90/50 mmHg) or uncontrolled high blood pressure (above 170/110 mmHg)
- Liver disease (sildenafil is metabolized by the liver; impairment increases drug levels)
- Severe kidney disease
- Retinitis pigmentosa or other hereditary retinal disorders
- Peyronie's disease or anatomical penile deformities
- Conditions predisposing to priapism: sickle cell disease, multiple myeloma, leukemia
- Active stomach ulcer or bleeding disorder
Drug Interactions
Sildenafil is metabolized primarily by the CYP3A4 and CYP2C9 enzyme pathways in the liver. Medications that affect these pathways can change how much sildenafil stays in your system.
Medications that increase sildenafil levels (your doctor may adjust or avoid):
- HIV protease inhibitors (ritonavir, saquinavir, indinavir): Ritonavir in particular dramatically increases sildenafil levels. Your doctor may adjust the dose or advise against the combination.
- Azole antifungals (ketoconazole, itraconazole): These inhibit CYP3A4, increasing sildenafil exposure.
- Macrolide antibiotics (erythromycin, clarithromycin): Moderate CYP3A4 inhibitors.
- Grapefruit juice: Contains compounds that inhibit CYP3A4. Regular consumption can increase drug levels.
Medications with additive blood pressure effects:
- Alpha-blockers (tamsulosin, doxazosin, prazosin): Used for high blood pressure or benign prostatic hyperplasia (BPH). Combined with sildenafil, they can cause significant drops in blood pressure. Your doctor may adjust the dose or timing, or advise against the combination.
- Antihypertensives (amlodipine, losartan, etc.): Sildenafil can add to the blood pressure-lowering effect. Usually manageable, but your doctor should know.
Other PDE5 inhibitors: Do not take sildenafil with tadalafil, vardenafil, or avanafil. Combining PDE5 inhibitors increases risk.
The NowExpress health assessment specifically screens for these interactions. This is why a proper medical review matters, and why buying from unregulated sources is risky.
What are the side effects of sildenafil?
Most men tolerate sildenafil well. Side effects are generally mild, dose-dependent, and temporary.
Very common (more than 1 in 10 men): - Headache
Common: - Facial flushing (redness or warmth) - Nasal congestion - Dizziness - Upset stomach or indigestion - Visual disturbances (blue-tinged vision, increased light sensitivity, blurred vision). This is linked to sildenafil's effect on PDE6 in the retina.
Rare but serious (seek immediate medical attention): - Priapism: An erection lasting more than 4 hours. This is a medical emergency. Untreated priapism can cause permanent damage. - Sudden vision loss (NAION, non-arteritic anterior ischemic optic neuropathy): Extremely rare but reported. Discontinue use and see a doctor immediately. - Sudden hearing loss: Also rare, sometimes with tinnitus (ringing in the ears).
If side effects are persistent or bothersome, your doctor can lower the dose or recommend switching to a different PDE5 inhibitor like tadalafil, which some men tolerate differently.
Is generic sildenafil the same as Viagra?
Generic sildenafil contains the same active ingredient as Viagra (sildenafil citrate) at the same strength. The difference is the manufacturer and the price.
Generic sildenafil contains the same active ingredient (sildenafil citrate), at the same dosage, manufactured to the same regulatory standards as branded Viagra. Generic manufacturers must demonstrate bioequivalence, meaning the drug is absorbed and acts in the body at the same rate and to the same extent as the branded version.
Why the price difference? Generic manufacturers sell the same molecule at a lower price than the branded product.
In the Philippines: At NowExpress (October 2026), Generic Sildenafil 50mg is around ₱750 for 4 tablets (about ₱190 per tablet), and Viagra (sildenafil) 50mg is around ₱4,400 for 4 tablets (about ₱1,100 per tablet). Prices can change; the product page shows the current price.
For a deeper look at the Viagra brand specifically, including how to verify authenticity and where to get it in the Philippines, see our Viagra Philippines guide.
Sildenafil and tadalafil are both prescription ED medicines. They differ in how long they stay active, per the label: up to about 4 hours for sildenafil and up to 36 hours for tadalafil. Your doctor helps you choose. For more, see Cialis vs. Viagra.
How do I get sildenafil in the Philippines?
You need a prescription from a licensed doctor. Sildenafil is a prescription medication in the Philippines, and buying it without a doctor's review is a risk to your health. This is a safety measure, not a bureaucratic hurdle. The drug interactions (especially with nitrates) can be fatal, so medical screening is essential.
Your options:
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Visit a doctor in person. See a urologist, internist, or general practitioner. They can evaluate your condition, check for contraindications, and write a prescription. You then fill it at a licensed pharmacy.
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Use a licensed online platform. NowExpress is an online pharmacy in the Philippines with an FDA License to Operate. It is LegitScript-certified, a licensed doctor reviews every order, and it delivers nationwide. The initial assessment is free: you complete a health assessment, a licensed Philippine doctor reviews your case, and if sildenafil is appropriate, they issue a prescription. The medication ships in discreet packaging. No clinic visit required. Genuine Viagra (made by Pfizer) is bought through the official Philippine import chain and dispensed by a licensed pharmacist.
A benefit of the online route for many Filipino men is privacy. ED carries significant stigma in Philippine culture. Many men delay treatment for years because of embarrassment. An online assessment removes the waiting room experience entirely.
Where NOT to buy sildenafil: unverified sellers on online marketplaces and social media, or any seller who does not require a prescription. These sources may sell counterfeit products with unknown ingredients, wrong dosages, or dangerous contaminants.
For more, see our sildenafil page or the ED treatment overview.
Frequently Asked Questions
Is sildenafil the same as Viagra?
Sildenafil is the active ingredient in Viagra. Pfizer's Viagra was the original branded version. Generic sildenafil contains the same compound at the same strength. The difference is the manufacturer and the price.
Can I take sildenafil every day?
Sildenafil is designed as an as-needed medication. The label maximum is one dose in 24 hours. Your doctor sets the dose and the timing. For daily use, ask your doctor about daily tadalafil (5mg).
Does sildenafil increase sexual desire?
No. Sildenafil improves the physical response to arousal. It does not increase libido or create desire. If low desire is your primary concern, the cause may be hormonal (low testosterone), psychological, or related to medications you are taking. A doctor can help identify the issue.
How long does sildenafil take to work?
Most men notice effects within 30 to 60 minutes. Heavy, fatty meals can delay the onset to 2 hours or more. Your doctor advises on timing.
Can I drink alcohol with sildenafil?
Alcohol can itself cause erectile difficulty, and combining it with sildenafil can increase dizziness and blood pressure drops. Ask your doctor what is right for you.
What if sildenafil does not work for me?
Talk to your doctor. Results can depend on things like meals, stress and other medicines, and your doctor can review those with you. They may adjust the dose (the label maximum is 100mg) or consider a different medicine such as tadalafil.
Is sildenafil safe for men with diabetes?
Sildenafil has been studied in men with diabetes. Diabetic men should have their cardiovascular health assessed first, as diabetes increases heart disease risk. Your doctor decides if it is right for you.
Can young men take sildenafil?
Sildenafil is approved for adult men (18+). ED in younger men is more common than people think, often linked to performance anxiety, stress, or lifestyle factors. A doctor decides if it is right for a younger man, and addressing the underlying cause is also important.
If you'd rather do this online, Start your free assessment and a licensed doctor will review it, or see Viagra (sildenafil) and Generic Sildenafil. Approved orders ship discreetly nationwide. Prices can change; the product page shows the current price.
Viagra is a registered trademark of Pfizer. This guide is for informational purposes. Sildenafil is a prescription medication. Consult a licensed doctor before use. Only for the treatment of conditions diagnosed by a physician.