Viagra, Cialis and the Rest: You Are Choosing a Duration, Not a Strength

Four drugs treat erectile dysfunction through the same mechanism, and a great deal of energy goes into working out which one is strongest. That is the wrong question. The trials that put them directly against each other find no meaningful difference in how well they work. What separates them is how quickly they start, how long they last, whether dinner matters, and which minor side effect you would rather have.

The efficacy question is settled, and the answer is dull

The American Urological Association lists sildenafil, tadalafil, vardenafil and avanafil together as first-line options and notes that they have similar efficacy in the general population. The guideline is also honest about a gap: the literature does not contain trials comparing every agent against every other one.

Where direct comparison does exist, it is thorough. A 2017 systematic review pooled 16 randomised trials of tadalafil against sildenafil, covering 5,189 men with a mean age between 36.9 and 56.2. On the erectile function domain of the IIEF, the pooled difference was 0.03 points (95% CI −0.32 to 0.39, p = 0.85). On sexual desire and on overall satisfaction, the pooled difference was 0.00.

A difference of 0.03 points on a 30-point scale is not a small effect. It is the absence of one. If a clinic, a telehealth service or a forum tells you that one of these is meaningfully stronger than another, that claim is not coming from the trial evidence.

What actually separates them

The real differences are pharmacokinetic, and they are large.

That half-life column is the entire decision. Sildenafil and vardenafil ask you to plan. Tadalafil does not, which is why it is often called the weekend drug, and why a 5 mg daily dose exists at all. Avanafil is the fastest to act, which matters to some men and to nobody else.

Food is a genuine consideration for some of them. A high-fat meal delays the absorption of sildenafil and vardenafil, so a large dinner can make a dose look like a failure when it was only late. Tadalafil is unaffected. On avanafil the two major guidelines disagree: the AUA table lists it as not affected by food, the European Association of Urology lists high-fat meals as delaying absorption. Where two guideline committees read the same labelling differently, the safe reading is the cautious one.

Different drugs, different complaints

Overall adverse event rates are the same. In the pooled comparison the odds ratio for any adverse event was 1.09 (p = 0.39), and headache, the most common complaint on all of them, was identical (OR 0.97).

The specific complaints are not identical:

• Muscle ache is far more common on tadalafil (OR 4.89, p = 0.004).
• Back pain is more common on tadalafil (OR 1.79, p = 0.03). It typically arrives 12 to 24 hours after the dose and settles on its own, which is exactly the pattern that makes men think they have injured themselves.
• Flushing is considerably less common on tadalafil (OR 0.39, p < 0.00001). If the visible red face is what bothers you about sildenafil, that is a real reason to switch.

Men in these trials preferred tadalafil by a wide margin (OR 8.04, 95% CI 4.99 to 12.96), and their partners preferred it by a wider one (OR 14.50, 95% CI 8.39 to 25.05). Confidence scores and treatment satisfaction scores moved in the same direction.

Read that preference finding carefully. These studies cannot be blinded in any useful sense, because a man notices whether a drug is still working the following afternoon. What the preference data mostly measures is the value of not having to plan. That is a real benefit, and it is not the same thing as the drug being better at producing an erection.

Daily dosing versus taking one when you need it

Tadalafil is the only one of the four licensed for daily use, and the comparison has been studied. The AUA guideline reports that on-demand and daily dosing produce the same level of efficacy, with daily dosing associated with lower adverse event rates, headache in particular. The EAU reaches the same conclusion and frames the choice around whether you want sex to be spontaneous.

So this is a preference and a budget question rather than a clinical one. Daily dosing usually costs more per month and removes the planning entirely. On-demand dosing costs less and asks you to think ahead by an hour or two.

Why it “did not work”

This is the most useful number in the whole guideline, and almost nobody is told it.

Among men who report that a PDE5 inhibitor did not work for them, incorrect use accounts for 56% to 81% of those failures. When men reporting non-response were simply re-educated about how to take the medication properly, the proportion who then succeeded rose from 23.6% to 58.5%. No new prescription, no dose increase, no second drug. The same tablet, used correctly.

The errors are consistent and unglamorous:

• Too few attempts. One disappointing night is not a trial of a drug. Dose titration is part of the treatment, not a sign it has failed.
• Never reaching the maximum dose. A great many men conclude a drug does not work for them without ever having taken the highest dose they could safely take.
• A large meal beforehand, on sildenafil or vardenafil.
• Taking it too close to sex. Thirty to sixty minutes is not a suggestion.
• Expecting the tablet to do the work. A PDE5 inhibitor amplifies a signal that arousal produces. It does not create that signal. Without sexual stimulation, nothing happens, and this single misunderstanding produces more perceived failures than any pharmacological problem.

There are also real medical reasons for non-response, and untreated low testosterone is the one most often missed. If the drug genuinely fails at maximum dose after several correct attempts, that is information worth taking back to a doctor rather than a reason to start ordering from somewhere unregulated.

The one absolute rule

Taking any PDE5 inhibitor with any organic nitrate can drop your blood pressure catastrophically. The EAU calls this an absolute contraindication, and it explicitly includes recreational amyl nitrite, sold as poppers. There is no small dose and no safe gap that makes this acceptable to improvise.

This is also why the drug you buy matters as much as the drug you choose. A tablet from an unregulated seller may contain a PDE5 inhibitor you were not expecting, at a dose nobody measured, which is a problem if you are one of the men for whom that interaction is dangerous. The supplement version of this problem is worse than most men assume.

One last thing worth holding on to. Erectile dysfunction is frequently the first visible sign of vascular disease, arriving some years before anything shows up in the chest. Choosing well between these four drugs is a reasonable thing to spend an afternoon on. Finding out what your blood pressure is doing is a better use of the same afternoon.

This article is for information only and is not medical advice. It cannot account for your individual circumstances. Talk to a doctor about your own situation, particularly before starting or stopping any prescription medication.