Sildenafil for erection problems

Key points about sildenafil

  • Sildenafil is used to treat erection problems.
  • Sildenafil is also called Viagra®, Vedafil® and Silvasta®.
  • Find out how to take it safely and possible side effects.
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Sildenafil is used for men with erection problems (erectile dysfunction). It works by increasing blood flow to the penis, to help achieve an erection. It will only work if you are sexually excited. Read more about erectile dysfunction. 

Sildenafil belongs to a group of medicines called phosphodiesterase type-5 (PDE5) inhibitors. They help to make a penis erect. Read more about PDE5 inhibitors.

In Aotearoa New Zealand sildenafil is available as tablets (25mg, 50mg and 100mg).

  • The dose of sildenafil can be either 25mg, 50mg or 100mg. The dose depends on your response and age.
  • Sildenafil is taken as a single dose before sexual activity. Do not take more than 1 dose a day.
  • Always take your sildenafil exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much sildenafil to take, how often to take it and any special instructions.

  • Timing: Take your dose 30 minutes to 1 hour before you intend to have sex. Sildenafil can keep working for up to 4 hours.
  • Swallow the tablet whole with a full glass of water. Do not take with grapefruit or orange juice.
  • You can take it with or without food. It may take longer to work if you take it with a heavy meal. Avoid excessive alcohol as it can lessen the sexual response.
  • Effectiveness: PDE5 inhibitors do not work for everyone – about 30% of men don't see an improvement. Many men need to try the medication a few (6–8) times before it works. If you don't have any improvement, do not increase your dose. Instead, talk to your doctor as there may be other treatment options.

Sildenafil is available on prescription from your doctor. It is not funded in Aotearoa New Zealand for general erectile dysfunction. None of the PDE5 inhibitor medications are funded in New Zealand for general erectile dysfunction. 

You can buy sildenafil directly from some pharmacies after a consultation with the pharmacist. Only pharmacists who have completed additional training can supply sildenafil. To make sure it is safe for you, they will measure your blood pressure and ask questions (such as what other medicines you are taking). You need to be aged 35–70 years to be eligible for this service. The pharmacy will also need to record your name and address. Here you can find Pharmacies that offer this service.(external link)

  • Have you ever had a stroke?
  • Do you have any heart or blood pressure problems?
  • Do you have an eye problem called optic neuropathy?
  • Do you have leukaemia (cancer of the blood cells) or multiple myeloma (a cancer of the bone marrow)?
  • Do you have sickle cell disease?
  • Do you have any disease or deformity of your penis?
  • Do you have any bleeding disorders?
  • Do you have a stomach ulcer?
  • Do you have kidney or liver problems?
  • Are you taking any other medicines including alpha blocker medicine (such as doxazosin, terazosin, prazosin)? 
  • Are you taking any over-the-counter and complementary medicines, eg, vitamins, minerals, herbal or naturopathic medicines?

If you have answered yes to any of these questions, it’s important that you tell your doctor or pharmacist before you take sildenafil. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Sildenafil has several medication interactions so check with your doctor or pharmacist before starting sildenafil. 

Serious medication interaction with nitrates

Nitrates and sildenafil should NOT be taken together, as both medicines together can cause a dangerous drop in blood pressure and collapse. Nitrates come in a variety of forms. Examples of nitrates are:

Like all medicines, sildenafil can cause side effects, but not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Blocked nose
  • Sensation of redness and warmth or burning of the face (called facial flushing)
  • These will pass quite quickly.
  • Headache
  • Dizziness
  • Muscle aches and pains
  • Tell your doctor if they bother you.
  • If dizzy, do not drive or operate heavy machinery.
  • Indigestion 
  • Tell your doctor if it bothers you.
  • An erection that lasts longer than 4 hours
  • Painful erection
  • Chest pain 
  • Rash or swelling of the face
  • Sudden problems with your eyesight such as loss of vision, in one or both eyes
  • Sudden loss of hearing  
  • Tell your doctor immediately or ring Healthline 0800 611 116.
For more information on side effects, see the Medsafe consumer information leaflets below.

Did you know that you can report a medicine side effect to the Centre for Adverse Reactions Monitoring (CARM)? Report a side effect to a product(external link)

Sildenafil (for erectile dysfunction)(external link) NZ Formulary, NZ
Viagra(external link) Medsafe Consumer Information Sheet, NZ
Silvasta(external link) Medsafe Consumer Information Sheet, NZ
Vedafil(external link) Medsafe Consumer Information Sheet, NZ


5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


  1. Phosphodiesterase type-5 inhibitors(external link) NZ Formulary 
  2. Sildenafil (external link)NZ Formulary 
  3. Viagra(external link) Medsafe Product Datasheet, NZ
  4. The hard facts on drug-induced priapism (long-lasting erections)(external link) Medsafe, NZ

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Maya Patel, MPharm PGDipClinPharm, Auckland

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