ED medicines compared: sildenafil, tadalafil, vardenafil and avanafil
Four medicines account for almost all tablet treatment of erectile dysfunction: sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra) and avanafil (Stendra). They work the same way, and the practical differences between them are how soon they start and how long they last.
What they have in common
All four are PDE5 inhibitors. Sexual arousal releases nitric oxide in the penis, which raises a messenger called cGMP; cGMP relaxes the blood vessels so blood flows in. PDE5 breaks cGMP down, and these medicines block PDE5, so the signal lasts longer. That is why none of them causes an erection on its own: they work only with sexual stimulation.
They also share their most important warnings:
- Never with nitrates. All four labels contraindicate them with nitrate medicines (such as glyceryl trinitrate for angina, or amyl nitrite “poppers”), because together they can lower blood pressure dangerously.
- An erection lasting more than 4 hours needs urgent medical help; without prompt treatment it can damage the penis permanently.
- Alpha-blockers and other blood pressure medicines can add to the drop in blood pressure.
- Heart health first. Sexual activity is a strain on the heart, so anyone with heart disease should ask a doctor whether it is safe.
How they differ
| Medicine | Example on this site | Starts working | Lasts |
|---|---|---|---|
| Sildenafil | Viagra | 30–60 minutes | 4–6 hours |
| Vardenafil | Levitra | 25–60 minutes | 4–5 hours |
| Avanafil | Stendra | 15–30 minutes | 4–6 hours |
| Tadalafil | Cialis | 30–60 minutes | 24–36 hours |
The times are the ones given on each product page and vary between people.
- Tadalafil stands apart for how long it lasts: its half-life is 17.5 hours, so one dose covers a day and a half. It is the only one of the four also used for an enlarged prostate, and it comes as a low daily dose (Cialis Daily) for men who prefer not to plan around a tablet.
- Avanafil is the quickest: it reaches its peak level 30 to 45 minutes after a dose taken without food, and its half-life is about 5 hours.
- Sildenafil and vardenafil sit in between. A heavy meal can delay them. Sildenafil is also used, at a lower dose, for pulmonary arterial hypertension.
- Udenafil (Zudena) is a fifth PDE5 inhibitor, developed in South Korea and less widely known.
The common side effects are similar across the group: headache, flushing, nasal congestion and indigestion. Tadalafil can also cause back pain and muscle aches.
Choosing between them
There is no single best medicine; it depends on how you use it. A shorter-acting medicine suits planned occasions, while tadalafil gives a longer window. If one does not suit you, another may. A doctor can check what is behind the erectile dysfunction, because it can be an early sign of heart disease or diabetes, and whether any of your other medicines rule one out.
All four come in more forms than a standard tablet: see generic ED medicines explained for oral jelly, chewable tablets and films that dissolve on the tongue.