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Sildenafil and tadalafil are medicines used to treat erection problems, more commonly known as erectile dysfunction (ED). They are both inhibitors of ‘phosphodiesterase type 5 (PDE5)’ and work in a very similar way. Phosphodiesterase 5 (PDE5) inhibitors are a type of drug that can affect blood flow and how cells communicate within the body [1,2].

For sildenafil and tadalafil to work, sexual stimulation must occur. Once aroused, the PDE5 inhibitors will work to relax the smooth muscle and increase the flow of blood into the penile tissue, resulting in an erection [1,2].

What are the differences between sildenafil and tadalafil?

Sildenafil

Sildenafil is medicine, taken in the form of a tablet, which can be used to treat the symptoms of erectile dysfunction (ED) in men over the age of 18. It starts to work 30 to 60 minutes after taking the medication and becoming sexually stimulated. The effects of sildenafil can last for up to four hours. To ensure the full effects of sildenafil, take one tablet with a glass of water, preferably on an empty stomach [1].

Sildenafil has been around since 1998 and is the active ingredient used in Viagra. Viagra was developed and is manufactured by a company called Pfizer. Pfizer had a patent on Viagra until 2013, which when it expired meant that other companies could manufacture their own erectile dysfunction medication. The only difference between Viagra and sildenafil is that sildenafil is a generic version of the medication rather than a brand name.  

You can take sildenafil to treat erectile dysfunction as and when needed, it is important however that you don’t take more than one tablet a day. 

You may experience some side effects from taking sildenafil. Side effects,[1] can include:

  • headaches 

  • sickness (nausea) 

  • feeling dizzy 

  • hot flushes 

  • blurred vision. 

Tadalafil

Much like sildenafil, tadalafil is the active, unbranded medicine used to treat erectile dysfunction. Tadalafil starts to work within 30 minutes of taking the medication and can be active for up to 36 hours, which allows for more spontaneity. Unlike sildenafil, you can take tadalafil with or without food [2].  

Tadalafil is the active ingredient used in the more well-known product Cialis. In 2003, a company named Eli Lilly introduced Cialis as an alternative ED medication. The company had the patent on tadalafil until November 2017 and, like sildenafil, this means that other companies can now use tadalafil to create their own erectile dysfunction medications.  

You might experience some side effects from taking tadalafil. Side effects[2] can include: 

  • headaches 

  • sickness (nausea) 

  • red or flushed face 

  • indigestion 

  • stuffy nose 

  • muscle aches. 

Published

February 2022

Next review

February 2024

Reviewed by

Gill Stone MRPharmS

Further reading on erectile dysfunction

What erectile dysfunction treatments are there?

Find out about some of the common erectile dysfunction treatment options to see what might work best for you.

How can I help my partner with erectile dysfunction?

Erection problems can happen naturally with age or due to being overweight or having other health conditions. Find out how you can support your partner.

How long does Viagra Connect (sildenafil) last?

Viagra Connect (sildenafil) can be active for up to 4 hours, though this will vary in different people. Learn about the effects of Viagra Connect here.

References

  1. 1.

    Sildenafil 50mg film-coated tablets - Summary of Product Characteristics (SmPC) - (emc). Accessed December 20, 2021.

    https://www.medicines.org.uk/emc/product/11740/smpc
  2. 2.

    Tadalafil 10 mg film-coated tablets - Summary of Product Characteristics (SmPC) - (emc). Accessed December 20, 2021.

    https://www.medicines.org.uk/emc/product/8636/smpc