Sildenafil vs tadalafil: what's the difference?

How do sildenafil and tadalafil work?

When a man is aroused, nerves in the penis release chemical signals that relax the smooth muscle in its blood vessels. The vessels widen, blood flows in and an erection develops. An enzyme called PDE5 then gradually switches that signal off.

Sildenafil and tadalafil block PDE5, so the signal lasts longer and blood flow is easier to maintain. That is why the group is called PDE5 inhibitors. Sildenafil was the first of these medicines to become widely known, under the brand name Viagra; tadalafil is sold under the brand name Cialis, among others, and both are also available as generic medicines in many countries.

Do they work without arousal?

No, and this is one of the most common misunderstandings. Neither tablet produces an erection on its own. They amplify the body's natural response to sexual stimulation. Without arousal, touch and a relaxed setting, not much happens.

This also explains why some men feel a tablet "did not work" the first time. Nerves, alcohol, a heavy meal or simply trying too hard can all get in the way.

Which lasts longer, sildenafil or tadalafil?

This is the main practical difference.

• Sildenafil acts for roughly four to five hours. It is usually taken some time before planned sex.
• Tadalafil has a much longer half-life, at about 17.5 hours, and can work for up to 36 hours. That window gives more room for spontaneity, which is why some people have nicknamed it "the weekend pill".

"Working for 36 hours" does not mean a 36-hour erection. It means the medicine can help an erection happen in response to arousal during that period. Tadalafil is also used in some countries as a lower daily tablet, and it has a separate role in treating urinary symptoms from an enlarged prostate. A doctor decides whether any of these approaches is appropriate.

Is one more effective than the other?

Major guidelines, including those of the European Association of Urology and the American Urological Association, do not name a single winner. The medicines in this family are considered broadly comparable in how well they work for most men. The choice usually comes down to timing, how often a man expects to have sex, side effects, other health conditions and personal preference.

Some men find one suits them better than the other. Guidelines also note that many men who believe a tablet has failed have not used it in the way their doctor intended, so a review with the prescriber is worthwhile before giving up.

What are the side effects?

Both share a similar set of common side effects, which are usually mild and short-lived: headache, facial flushing, a blocked nose and indigestion. Sildenafil is more often associated with temporary changes in colour vision, and tadalafil with back or muscle aches.

Any erection that lasts more than four hours, painful or not, needs urgent medical attention.

Who should not take them?

The most important rule is that neither medicine must be combined with nitrates, such as glyceryl trinitrate sprays or tablets used for angina. Together they can cause a dangerous fall in blood pressure. Care is also needed with some other medicines, including certain alpha-blockers.

Because erectile dysfunction and heart disease share risk factors, the Princeton III consensus recommends that a man's cardiovascular health is assessed as part of ED treatment. Sexual activity itself places a demand on the heart, and a doctor needs to be sure that is appropriate.

What to take away

Sildenafil and tadalafil are well-studied, widely used medicines that work in the same way. The difference is mainly about timing, not strength. Both are prescription medicines in many countries, and buying them from unregulated websites carries the risk of fake or contaminated products. The right choice, and the right way to take it, is a decision for a doctor who knows your health and your other medicines. Our erectile dysfunction guide explains the wider range of treatments.

Questions men also ask

Is tadalafil stronger than sildenafil?

Not in a simple sense. Guidelines treat the medicines in this family as broadly comparable in effectiveness; the practical difference lies mainly in how long they last.

Can I switch from one to the other?

Some men who do not get on with one medicine are offered the other. That decision, and how to take it, should be made with a doctor.

Do these tablets increase sex drive?

No. They act on blood flow in the penis, not on desire. Low desire has different causes and needs a separate conversation.

Sources & further reading

1. European Urology European Association of Urology Guidelines on Sexual and Reproductive Health—2021 Update: Male Sexual Dysfunction (opens in a new tab) (2021) Salonia A, et al.
2. Journal of Urology Erectile Dysfunction: AUA Guideline (opens in a new tab) (2018) Burnett AL, et al.
3. Mayo Clinic Proceedings The Princeton III Consensus recommendations for the management of erectile dysfunction and cardiovascular disease (opens in a new tab) (2012) Nehra A, et al.

This article is general health information. It does not replace an individual medical consultation, examination or diagnosis. Read our editorial policy and medical review policy.