Sildenafil, tadalafil and avanafil compared

The first-line treatment for erectile dysfunction is a PDE5 inhibitor, a tablet that increases blood flow to the penis when you are aroused. Three are licensed and widely used in the UK: sildenafil (the active ingredient in Viagra), tadalafil (Cialis), and avanafil (Spedra). They work in the same way. The differences are in how fast they start, how long they last, and how they suit your life. This article compares them so the choice makes sense.

How they all work

When you are sexually aroused, nerves release nitric oxide, which relaxes the arteries in the penis so blood flows in. An enzyme called PDE5 normally switches that signal off. A PDE5 inhibitor blocks the enzyme, so the relaxing signal lasts longer and an erection is easier to get and keep. Crucially, all three need sexual stimulation to work. They are not aphrodisiacs and they do not produce an erection out of nowhere.

Sildenafil

Sildenafil is the longest-established option. It is taken about an hour before sex and lasts roughly 4 to 6 hours. It works best on a relatively empty stomach, because a heavy or fatty meal slows absorption and can blunt the effect.

It is the default starting point for many men: well understood, effective for most, and taken only when needed. Common starting strengths are 50mg, adjusted up or down based on response and side effects.

Tadalafil

Tadalafil stands out for its duration. A single on-demand dose lasts up to 36 hours, which is why it is sometimes nicknamed the weekend tablet. That long window means you do not have to time things as tightly, and food does not affect it much.

Tadalafil also comes as a low daily dose (2.5mg or 5mg) taken every day, which keeps a steady level in your system and removes planning altogether. Whether on-demand or daily suits you better is covered in On-demand vs daily tadalafil.

Avanafil

Avanafil is the newest of the three. Its main feature is speed: it can start working in about 15 to 30 minutes, faster than sildenafil for many men, and it lasts a similar length of time. It is a useful option where sildenafil has worked but the onset feels too slow, or where side effects from the others have been troublesome.

A fourth option you may have heard of

There is a fourth PDE5 inhibitor, vardenafil (Levitra), which works in the same way as sildenafil with a similar onset and duration. It is used less often now that the other three cover the same ground, but it exists and may come up. The principle holds across all of them: same mechanism, small differences in timing and tolerability, and the choice is about fit rather than potency.

Choosing between them

There is no single best tablet; there is the one that fits you. A few practical pointers:

If you prefer spontaneity over a long window: a fast on-demand tablet such as sildenafil or avanafil taken ahead of time.

If you dislike planning around a tablet: tadalafil, either as a long on-demand dose or as a low daily dose.

If sex tends to follow a meal out: tadalafil or avanafil, which are less affected by food than sildenafil.

If cost matters: sildenafil is the long-established generic and usually the most economical.

Give any choice a fair trial of six to eight attempts before deciding it does not suit you. Performance anxiety can interfere with the first few tries, and confidence builds once you have had a success.

Safety applies to all three

All PDE5 inhibitors share the same absolute rule: they must never be taken with nitrate medication (such as GTN for angina) or nitrate-based recreational drugs (poppers), because the combination can cause a dangerous fall in blood pressure. They are also used with caution alongside some other blood-pressure medicines, including alpha-blockers. The assessment screens for all of this, which is why ED treatment is prescribed after a clinical review rather than picked off a shelf.

If the first medication does not work, switching is straightforward; see What to do when the first ED treatment does not work.

What to expect on a first prescription

Most men start on a single, well-established tablet at a middle dose and take it only when needed, then adjust from there. The first prescription is a starting point, not a final answer: you try it a handful of times, see how you respond and how you tolerate it, and the dose or the drug is fine-tuned at your review. There is no need to settle for the first thing if it is not quite right, and no need to commit to a daily medicine before you know one works for you.

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