Sildenafil — What it does, how to use it, and how to stay safe

Sildenafil (the active ingredient in Viagra and Revatio) is a common medicine for erectile dysfunction (ED) and some cases of pulmonary hypertension. It relaxes blood vessels by blocking the enzyme PDE5, which helps increase blood flow where it’s needed. That’s the quick version. Below you’ll find practical dosing tips, common side effects, major interactions, and smart ways to buy it online without getting burned.

How to take sildenafil

For ED, people usually take 25–100 mg as needed, about 30–60 minutes before sex. It works faster on an empty stomach and lasts around 3–5 hours for most men. Tadalafil (Female Cialis/Tadalafil) lasts much longer, so if you want a different profile, read our guide “Navigating Female Cialis Purchase Online.” For pulmonary arterial hypertension (PAH), the prescription and schedule differ — tablets called Revatio are often taken multiple times a day at lower doses. Always follow your prescriber's instructions, and don’t double up doses.

Missed a dose? For as-needed ED use, you don’t need to make it up. For scheduled PAH dosing, take it as soon as you remember unless it’s nearly time for the next dose.

Side effects and interactions — what to watch for

Common side effects: headache, flushing, nasal congestion, upset stomach, and sometimes temporary changes in color vision (a blue tint). Most side effects are mild and pass quickly.

Big red flags: nitrates. If you’re using any nitrate medication (nitroglycerin, isosorbide), do NOT take sildenafil — the combo can cause dangerous drops in blood pressure. Also be careful with alpha-blockers, some blood pressure meds, and strong CYP3A4 inhibitors (like ritonavir or certain antifungals) which can raise sildenafil levels. Alcohol can make dizziness or low blood pressure worse. If an erection lasts more than 4 hours, get urgent medical help — that’s priapism and can cause permanent damage.

If you have heart disease, recent stroke, uncontrolled high blood pressure, or severe liver/kidney problems, talk to your doctor before trying sildenafil.

Want practical buying tips? Read on.

Many articles on this site cover buying meds online safely — check our guides about online pharmacies and safe purchases. Here are quick, useful checks:

• Make sure the pharmacy requires a prescription and lists a real address and phone number.
• Look for HTTPS on the site, clear contact info, and pharmacist access.
• Avoid unbelievably low prices or huge multi-month supplies from unknown sellers.
• Check reviews from multiple sources and look for third-party pharmacy verifications where available.
• When your pills arrive, confirm the packaging, batch number, and expiry date. If anything seems off, don’t take them and contact a pharmacist.

Want more? Read our posts about safe online pharmacies and comparing drug options to make smarter choices. If you’re unsure whether sildenafil fits your health profile, talk to your doctor — and bring these practical questions: possible interactions, exact dosing for your situation, and what to do if side effects occur.

Use meds safely, stay informed, and if you have doubts, ask a healthcare professional before buying or taking sildenafil.