The difference that actually matters

Both drugs block the same enzyme by the same mechanism. What separates them is pharmacokinetics: tadalafil's half-life is roughly four times longer, which changes the experience of using it far more than it changes the erection itself.

With sildenafil, you take a tablet, wait, and have a window. With tadalafil taken on Friday evening, that window covers most of the weekend. With daily low-dose tadalafil, there is no window — the drug is simply always present.

Choose sildenafil if

  • Cost is the deciding factor — it is usually the cheapest option available.
  • You have sex once a week or less, and generally know in advance.
  • You would rather the drug clear your system quickly.
  • You have cardiac disease and the shorter nitrate window matters to you.
  • You have had back or muscle ache on tadalafil.

Choose tadalafil if

  • You dislike planning sex around a tablet — this is the most common reason men prefer it.
  • You have sex more than twice a week, which makes the daily dose attractive.
  • You also have urinary symptoms from an enlarged prostate.
  • You often eat a substantial meal before sex.
  • You have had visual side effects on sildenafil.
  • Performance anxiety is significant, and separating the tablet from the sexual event would help.

Switching between them

If the first choice does not work well after a genuine trial — four to eight attempts at the maximum tolerated dose, taken correctly — switching to the other is standard and sensible. Some men respond considerably better to one than the other for reasons that are not well understood.

Do not take them on the same day, and do not overlap the end of one with the start of the other without your prescriber's guidance. Give tadalafil a couple of days to clear before starting a different regimen.

FAQ

Frequently asked questions

Which works better, Viagra or Cialis?
Neither. Response rates are comparable. Preference studies favour tadalafil, and the reason given is almost always the longer window rather than a firmer erection.
Can I take both?
No. Do not combine PDE5 inhibitors. It raises the risk of low blood pressure and priapism without improving the result.
Which is cheaper?
Generic sildenafil is usually slightly cheaper, but both are inexpensive as generics. Prices vary considerably between pharmacies.
Which has fewer side effects?
They have similar overall rates but different characteristic effects — visual disturbance with sildenafil, back and muscle ache with tadalafil. Avanafil is the most selective and often the best tolerated.
Sources

What this is based on

We link to primary sources — clinical guidelines, regulator publications and peer-reviewed research — wherever possible. Links open on third-party sites we do not control.

  1. [01]U.S. Food and Drug Administration. Drugs@FDA — approved drug products and prescribing information.
  2. [02]American Urological Association. Erectile Dysfunction: AUA Guideline (2018).
  3. [03]MedlinePlus (National Library of Medicine). Drugs, Herbs and Supplements.