Visit Mayo Clinic Men’s Health to get started. Here are some steps that might help: If you smoke, quit. If medication is prescribed, is there a generic alternative? Include physical activity in your daily routine. Take sildenafil up to 4 hours before you want to have sex.How long does Viagra take to work? Viagra works quickly after you take a dose. In most males,* Viagra works within 1 hour after it’s taken. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex. For sildenafil to work properly, you’ll need to be sexually excited. 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 .