Sildenafil and tadalafil are the two most common treatments for erectile dysfunction. Both have a long track record, and both are sold as lower-cost generics. The real question is usually not which one is "better", but which one suits the way you live.
Sildenafil is usually taken about an hour before sex and lasts around four to five hours. A high-fat meal can delay the effect. Tadalafil, on the other hand, can last for up to 36 hours, and food has little effect. Many men also take a low daily dose of tadalafil so they do not have to plan ahead.
For a side-by-side look, see this plain-English guide covers doses, timing and safety.
Before you start: never take either medicine with nitrate tablets or sprays for chest pain or with "poppers". Let your doctor know about any alpha-blockers. The usual side effects are headache, flushing, more info a blocked nose and indigestion. Get urgent help for an erection lasting more than four hours or any sudden loss of sight or hearing.
Do not chase higher strengths. The licensed doses are 25, 50 or 100 mg for sildenafil and 2.5 to 20 mg for tadalafil. Bigger doses do not reliably work better, but they do make side effects more likely. Stick to the dose on your prescription.
When you buy medicine online, make sure the strength matches your prescription and keep the leaflet. A valid prescription is required for every order of a prescription medicine. There is more detail on this page.
This article is for general information only. Speak to your doctor or pharmacist before starting any medicine.