Sildenafil vs tadalafil: what really sets them apart

It is one of the most searched questions about erectile dysfunction: sildenafil or tadalafil? Plenty of mythology circulates: that one is "stronger", that the other "lasts 36 hours", that you only need to compare the milligrams. None of it holds up to a serious reading of the product information. Both are type 5 phosphodiesterase inhibitors (PDE5 inhibitors), both are marketed in Spain with generics authorised by the AEMPS and both share the same mechanism. The differences do exist, they matter, and they mostly come down to pharmacokinetics, food and the approved indications of each one. We go through them one by one here, without recommending either: that decision belongs to a doctor who has assessed you.

What they have in common: the mechanism and the essential condition

Sildenafil and tadalafil belong to the same drug family, the PDE5 inhibitors. They act on the biochemical pathway that allows the smooth muscle of the corpora cavernosa to relax so that blood can flow in. The key point, often overlooked, is that this pathway is only activated when there is desire and stimulation: the sildenafil product information says so plainly, "sexual stimulation is required for sildenafil to be effective". These are not aphrodisiacs and they do not work from a standing start. If someone takes a tablet, sits down on the sofa and waits for something to happen, nothing will, and that does not mean the medicine is no use to them.

If you want the detail on how one of them works internally and what the trials show, we cover it in our guide on how sildenafil works and what the evidence says.

The big difference: how long each one stays in the body

The figure that genuinely separates the two active ingredients is the elimination half-life, that is, the time the body takes to halve the concentration of the drug. According to their product information, the half-life of sildenafil is 3 to 5 hours (around 4) and that of tadalafil 17.5 hours. That is a roughly fourfold difference, and it explains why one tends to be called "short-acting" and the other "long-acting".

It is worth being precise about what that figure means and what it does not. Half-life describes how long the drug remains in the blood, not a promise of a neatly rounded window of effectiveness. The number of hours that has become popular for tadalafil does appear in its product information, but with a different meaning: in trials with 1,054 patients, it improved erectile function compared with placebo up to 36 hours after the dose, an average trial result and not a guaranteed window for each person. In practical terms: tadalafil remains in the body considerably longer, which translates into a regimen less tied to the clock; sildenafil is cleared sooner, which means planning more closely around the moment.

The 2025 EAU guideline in fact includes a comparative table of pharmacokinetic parameters for the PDE5 inhibitors (Tmax, Cmax, AUC, half-life) with data adapted from the EMA, precisely because these details shape the clinical choice more than anything else.

Food: a factor that affects only one of the two

Here the difference is clear and practical. Tadalafil can be taken with or without food, whereas with sildenafil food slows absorption: according to its product information, taken with food it is absorbed more slowly and the onset of the effect may be delayed. Translated into real life: a heavy dinner before taking sildenafil can delay the moment it starts to work, whereas with tadalafil that factor is not on the table. It is no small detail for anyone who associates sexual activity with dinner, which is to say almost everyone.

The regimens approved in Spain: what the product information says

This section is for information, not a regimen for you. Any dose and any adjustment is a matter for the doctor who assesses you, because they depend on your medical history, your other medicines and your kidney, liver and cardiovascular status.

Sildenafil

According to the Viagra product information on CIMA-AEMPS, the dose is 50 mg taken as needed approximately one hour before sexual activity; it can be increased to 100 mg or reduced to 25 mg, and the maximum recommended dose is 100 mg once a day. In severe renal impairment (creatinine clearance below 30 ml/min) and in hepatic impairment, for example cirrhosis, the 25 mg dose should be considered; in mild or moderate renal impairment (30–80 ml/min) the usual doses are used. It is not indicated in people under 18. As well as film-coated tablets, an orodispersible 50 mg presentation is available in Spain.

Tadalafil

The Cialis product information sets out two different scenarios. As needed: 10 mg before anticipated sexual activity, with or without food, and 20 mg can be tried if 10 mg is not adequate; it can be taken from at least 30 minutes beforehand, with a maximum frequency of one tablet a day. Frequent use: the 10 and 20 mg doses are not recommended for continuous daily use, but for those who anticipate frequent use (at least twice a week) a daily 5 mg regimen taken at the same time each day may be appropriate, with periodic reassessment of whether to continue it. It is likewise not indicated in women.

The indication only tadalafil has: the prostate

This is probably the most underrated difference in online comparisons. Tadalafil 5 mg once a day is approved for benign prostatic hyperplasia in adult men; sildenafil does not have that indication. For a man dealing with erection problems and lower urinary tract symptoms at the same time —getting up at night, a weak stream, urgency— that changes the clinical conversation entirely, because a single treatment can address both fronts. It is exactly the kind of nuance that only emerges when someone takes a proper medical history.

What the European guideline says about choosing

The 2025 EAU guideline, drawing on two meta-analyses, points towards using sildenafil 50 mg in patients who prioritise efficacy and towards starting with tadalafil 10 mg in those who prioritise tolerability. Note the wording: it does not say that one is better, it says the choice depends on what matters most to each person. And the guideline itself recommends individualised treatment selection, as well as addressing comorbidities and lifestyle: weight loss, glycaemic control, stopping smoking and physical activity.

There is another finding in the same guideline that almost nobody mentions and that helps make sense of online testimonials: PDE5 inhibitor trials show a significant placebo response, that is, there was also significant improvement in erectile dysfunction in the groups given placebo. That does not invalidate the drugs, but it does explain why isolated personal experiences are a poor gauge.

The guideline adds two important clinical nuances. One, cardiovascular: it incorporates the Princeton Consensus Conference IV update on the use of PDE5 inhibitors in low-risk patients who use or have ready access to nitrates, with algorithms that include the coronary calcium score. Two, hormonal: if erectile dysfunction coexists with biochemical hypogonadism, testosterone can be considered as initial treatment, adding a PDE5 inhibitor if the erectile response is incomplete. That is why it is worth being able to recognise the real symptoms of low testosterone before assuming the problem is purely one of erections; and if the diagnosis is confirmed, it helps to understand what testosterone therapy involves and what to expect from it.

Interactions, and why this needs to go through a doctor

The clearance of sildenafil is reduced by CYP3A4 inhibitors such as ketoconazole, erythromycin or cimetidine, which means that certain common medicines alter exposure to the drug. Add the adjustments for kidney or liver function and the cardiovascular risk assessment set out in the European guideline, and it becomes clear why the "sildenafil vs tadalafil" comparison is not settled with a table: it is settled with a medical history. Both are medicines, not supplements, and the prior assessment exists for a reason.

In summary, and what you can do today

What to take away: there is no universal winner between sildenafil and tadalafil. They share a mechanism and the need for sexual stimulation, and they differ in half-life, in the influence of food, in the approved regimens and in the fact that only tadalafil is indicated for benign prostatic hyperplasia. The choice is a clinical one, not a forum one, and before choosing it is worth looking at what the European guideline itself asks you to look at: if there is a hormonal problem behind the erection, the approach changes. For that part, what does exist in Spain today is male hormonal health treatment, with a prior assessment, a prescription from a registered doctor when appropriate and ongoing follow-up. If you want to know whether this is your case, you can check whether you are eligible.