Its effects often last for 4 to 5 hours. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. While each PDE5 inhibitor differs slightly, they’re very similar in treating erectile dysfunction. Those who don’t feel comfortable discussing ED with an in-person provider or lack time to visit a doctor’s office may find online ED prescriptions beneficial. This medicine works best when you take it on an empty stomach an hour before sex. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects.Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects often last for 4 to 5 hours. It might work longer if you have mild to moderate erectile dysfunction. Vardenafil. Sildenafil is used to treat erectile dysfunction (ED) and to reduce blood pressure in pulmonary arterial hypertension (PAH). It is taken when needed for ED and daily for PAH. A headache, stomach upsets, and flushing are the main side effects, and it should not be taken within 24 hours of a nitrate. Best Low Cost: GoodRx Fastest Delivery: Blink Health: Sesame Sign Up Now Key Specs Cost: Consultation prices vary based on the prescriber; $5 generic prescriptions Medical Consultation Required: Yes Medications Prescribed: Viagra, Cialis, sildenafil, tadalafil Generic offered: Yes Why We Chose It.