Frequently asked questions about PDE5 inhibitors

Sildenafil (Viagra, Silvasta, Vedafil), tadalafil (Cialis) and vardenafil (Levitra)

PDE5 inhibitors are a group of medicines used to improve erections.

Common examples of PDE5 inhibitors are sildenafil (Viagra, Silvasta, Vedafil), tadalafil (Cialis) and vardenafil (Levitra).

How do PDE5 inhibitors work?

These medicines help to make a penis erect. They enable erections to be achieved and maintained more easily but they do require sexual stimulation to work. 

PDE5 inhibitors work by opening the blood vessels supplying your penis. This causes a greater blood flow into your penis and improves your erection. They may not work in severe erectile dysfunction or where the natural erectile mechanism has been irreversibly damaged. Read more about erectile dysfunction.

PDE5 inhibitors are most effective when used together with lifestyle changes, such as weight loss, increased physical activity, cutting out smoking, getting enough sleep and reducing alcohol. These can all have a big effect on erectile dysfunction. 

PDE5 inhibitors 
have no effect on your libido (sexual desire), ejaculation or fertility. 

Is there any difference between PDE5 inhibitors?

The PDE5 inhibitors (sildenafil, tadalafil, vardenafil) are all similarly effective. They work well for most men with erectile dysfunction, allowing intercourse (or sex) in about 70% (7 out of every 10) users. Sildenafil and vardenafil need to be taken on an empty stomach but tadalafil may be taken with food.

How should a PDE5 inhibitor be taken?

Timing

Depending on the medication you are prescribed, a tablet should be taken between 30 minutes and 1 hour before sexual intercourse. Hands-on stimulation is still required to obtain an erection. The medicine should be taken in a relaxed setting.

Food may affect it

Fatty meals and large amounts of alcohol can interfere with the body’s absorption of these medicines. Sildenafil and vardenafil need to be taken on an empty stomach due to delayed absorption from food, but not tadalafil.

Can I take it every day?

Usually it's best not to take more than one normal dose in 24 hours, but there are low-dose options that can be taken every day. The daily low-dose option is used for people who have sex more than twice weekly. It will cause an erection whenever you are sexually stimulated. Since the dose is lower, it may take up to 1 week from starting the medication to get the full effect.

When is it not safe to take PDE5 inhibitors?

PDE5 inhibitors are not suitable for everyone. They may not be safe if you have certain medical conditions, such as if you have had a recent stroke, unstable angina or myocardial infarction, or if your blood pressure is not well controlled.

PDE5 inhibitors should also not be used if you are taking some medications. PDE5 inhibitors and nitrates (eg, GTN spray or isosorbide mononitrate), which are used for chest pain and other heart conditions, should NOT be taken together, as the two medicines together can cause a dangerous drop in blood pressure and lead to collapse. 

Ask your doctor or pharmacist to check all the other medicines you are taking before you start taking a PDE5 inhibitor to make sure they are safe to take together.

What are the side effects of PDE5 inhibitors?

The most common side effects include headache (12%), flushing (10%) and indigestion (7%). Some people have problems with their vision (blue-tinged) and dizziness (3%). If dizziness does occur, you should not drive or operate heavy machinery.

It is important that you report any severe side effect to your doctor or pharmacist.

How do I get PDE5 inhibitors?

Sildenafil, tadalafil or vardenafil is available on prescription from your doctor. None of the medications are funded in New Zealand for general erectile dysfunction. The generic options are normally cheaper than the branded ones and work the same (eg, Silvasta or Vedafil instead of Viagra). 

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 need to measure your blood pressure and ask questions (such as what other medicines you are taking). They will also need to record your name and address. 

What do I do if PDE5 inhibitors are not working?

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. The first few times you use these medicines, there may be some anxiety if you have not had sex for some time.

If you don't have any improvement, do not increase your dose. Instead talk to your doctor. There may be other treatment options.

References

  1. Sexual dysfunction in men; when Viagra doesn't work Goodfellow Unit, NZ
  2. Erectile dysfunction BPAC, NZ, 2008
  3. Erectile problems Best Health, UK, 2014
  4. Dietary supplements for erectile dysfunction – a natural treatment for ED?  Mayo Clinic, US, 2017 
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland; Reviewed By: Dr Jeremy Steinberg, FRNZCGP Last reviewed: 19 May 2020