Sildenafil: What It Does, How to Use It, and How to Stay Safe

Sildenafil is one of the most common oral treatments for erectile dysfunction (ED). It helps many people get and keep erections by increasing blood flow to the penis. It also has a medical use for pulmonary arterial hypertension in a different dose. If you’re thinking about sildenafil, this page gives straight, practical advice—how it works, common side effects, dosing basics, interactions to watch for, and tips for buying safely online.

How sildenafil works and when to take it

Sildenafil usually starts working in 30–60 minutes and can last up to four hours. For faster effects, take it on an emptier stomach—heavy meals can slow it down. Typical starting doses are 25 mg, 50 mg, or 100 mg depending on your health and what your doctor recommends. Start low if you’re unsure and only change dose after talking to your prescriber. Remember: sexual stimulation is still required for it to work.

Also note that sildenafil used for ED is different in labeling and dose from formulations prescribed for lung conditions. Never switch doses or brands without medical advice.

Safety, side effects, and interactions

Common side effects are headache, flushing, nasal congestion, upset stomach, and dizziness. Most are mild and fade after a few hours. Stop and get medical help if you have chest pain, fainting, a sudden painful or prolonged erection (over 4 hours), sudden loss of vision, or severe shortness of breath.

Do not take sildenafil with nitrates (often used for chest pain) or riociguat—this combo can cause a dangerous drop in blood pressure. Be cautious if you take alpha-blockers, some blood pressure meds, or certain HIV and hepatitis C treatments. If you have heart disease, low blood pressure, or recent stroke/heart attack, check with your doctor first.

Alcohol and large, fatty meals can reduce effectiveness and increase side effects. Grapefruit or grapefruit juice may affect how the drug is broken down, so avoid large amounts while using sildenafil.

If you’re on other prescriptions, bring a full list to your provider so they can check for interactions.

Thinking about buying sildenafil online? Be careful. Choose pharmacies that require a prescription, show clear contact info, use secure checkout (HTTPS), and have real reviews. Avoid extremely low prices that seem too good to be true—counterfeit pills are a real risk. If possible, use a reputable pharmacy you can call or one recommended by your healthcare provider. Keep prescriptions and receipts.

Want alternatives or more comparisons? We cover Tadalafil and other PDE5 inhibitors elsewhere on the site, which can help you weigh onset time, duration, and side effects. If sildenafil isn’t a fit, your doctor can suggest a safer or more effective option tailored to your health and lifestyle.

Final tip: honest talk with your clinician matters. Bring up other meds, heart symptoms, and any questions about sexual activity after a heart event. That short conversation keeps treatment safe and effective.