Sildenafil is a frequently-prescribed medication used to treat erectile dysfunction (ED). Sildenafil uses the active ingredient sildenafil citrate, which can help blood vessels relax and make it easier to achieve an erection. Sildenafil tablets are also used for the treatment of pulmonary hypertension.

What is Erectile Dysfunction?

Erectile dysfunction (ED) is classified as the persistent inability to get an erection. This can include being unable to sustain an erection long enough to have satisfactory sex. This can have many causes, which can be physical (diabetes, heart disease etc.), psychological (stress, anxiety etc.) or a mix of both.

For more detailed information, you can read our blog posts on the Physical Causes of ED, and the Psychological Causes as well.

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What is the Difference Between Sildenafil and Viagra?

Sildenafil and Viagra both use the same active ingredient (sildenafil citrate). Viagra is the branded version, while sildenafil is the generic version. They operate the exact same way, and are as effective as each other. The only real differences are the appearance of the tablets (Viagra tablets are diamond-shaped and blue) and the price – sildenafil is much more affordable than Viagra.


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How Does Sildenafil Work?

Erections depend on three main factors: relaxation of the corpus cavernosum (smooth muscle comprising most of the penis, which relaxes to allow blood to move in), increased blood flow (blood moving into blood vessels of the penis) and restricted blood outflow in the penis (less blood moving out of the penis to maintain the erection).

This physiological mechanism is increased by Sildenafil, which is one of a class of drugs called PDE inhibitors named for its inhibition of an enzyme called phosphodiesterase type 5 (PDE5). Sildenafil therefore increases the strength of your erection following sexual arousal. Please note, this does not mean you will have random erections – you will still need to be sexually stimulated to achieve an erection.

When used for pulmonary hypertension, Sildenafil works by relaxing blood vessels supplying the lungs.

Who is Sildenafil For?

Sildenafil tablets used for erectile dysfunction are safe to take for most men over 18. If used for pulmonary arterial hypertension (high blood pressure), it is safe for most men and children over the age of 1. Sildenafil is not recommended if you are taking certain medications, have some medical conditions (such as heart problems) or have certain allergies. If you are unsure whether you should take Sildenafil, please read the Patient Information Leaflet and call your doctor for medical advice.

What Happens if You Overdose on Sildenafil?

Like with any medication, adverse effects are possible if you take Sildenafil in excess (more than once daily or in a dose that is higher than suggested). The normal dose of Sildenafil is 50 mg. This may be increased to 100mg in some cases, but you should only take the strength your doctor has prescribed.

Overdosing on Sildenafil may result in a reduction in blood pressure, which might result in:

  • Vision alterations, including blurred vision, colour shifts, and light sensitivity 
  • Sudden hearing loss or ear ringing 
  • Shortness of breath or chest pain 
  • Light-headedness, fainting, or confusion 
  • Headache


If you suspect a Sildenafil overdose, get emergency medical attention immediately.

An extended, uncomfortable erection, also known as priapism, is a more dangerous side effect of taking too much Sildenafil. You should seek medical attention right away if you’ve taken Sildenafil and experience an erection that lasts longer than four hours and isn’t eased by ejaculation. If unattended, this could harm your penis permanently.

What are the Side Effects of Sildenafil?

All medications can cause unwanted side effects; Sildenafil is no different. Some of the most common side effects include:

  • Headache
  • Nausea/dizziness
  • Indigestion
  • Stuffy nose
  • Flushes
  • Diarrhoea
  • Trouble sleeping


For a full list of possible side effects and contraindications, please read the Patient Information Leaflet.

Pros and Cons of Sildenafil

Pros Cons
Proven effective in treating ED for up to 74% of men Can cause side effects such as those mentioned above
Fast-acting (within one hour of taking) and long-lasting (up to 4 hours after taking) Can interact with other medications to cause negative side effects, and may interact with food after meals to reduce effectiveness
Cheaper than branded counterparts (eg. Viagra) and widely available (eg. buying online) Not suitable for those with certain medical conditions

What are the Alternatives to Sildenafil?

There are multiple ED medications on the market; however, most work in a similar way to sildenafil (i.e. they are mostly PDE5 inhibitors).

Cialis is the main branded competitor to Viagra, and does operate in a slightly different way. Rather than taking a pill before you have sex, Cialis is taken at any time of the day, with the effects lasting for a longer period. This allows you to be more spontaneous with sex, and may allow for multiple erections across the treatment time.

Cialis is also available as a generic medication, Tadalafil. Much like Sildenafil is to Viagra, Tadalafil is just as effective as Cialis, but is a lot more affordable for regular use.

Other alternatives, such as Levitra (Vardenafil) and Spedra (Avanafil) are also available.


  • Sildenafil is a common drug for ED (erectile dysfunction), but is also less commonly used for pulmonary hypertension.
  • It is a cheaper alternative to Viagra, and several alternative medications exist.
  • Side effects may rarely occur with or without excess use.