PDE5 Inhibitors (Viagra, Cialis, Levitra)

The oral medications for Erectile Dysfunction, impotence, are called, Phosphodiesterase-5, or PDE5 inhibitors in short. There are 3 types of PDE5 inhibitors available in Australia:

  • Viagra (Sildenafil), which has been available since 1998
  • Cialis (Tadalafil), which has been available since 2003
  • Levitra (Vardenafil), which has been available since 2003

How do these PDE5-Inhibitors work?

Erectile DysfunctionPDE5 inhibitors help the body's natural response to sexual stimulation, since they block the enzyme Phosphodiesterase-5 in the smooth muscle cells in the penis.

In the smooth muscle cell GMP is always present, when Nitric Oxide enters the smooth muscle cell it converses GMP into cyclic GMP (cGMP), which causes an erection.

cGMP is normally reduced by the enzyme Phosphodiesterase-5, but the PDE5 inhibitors prevent this enzyme from working. This means that cGMP stays in the smooth muscle for longer, which means more erection.

So really, these PDE5 inhibitors do not cause erections, but they help the body's normal response to sexual stimulation.

Side-effects of PDE5 inhibitors (Viagra, Cialis, Levitra)

Common side effects of Viagra, Levitra and Cialis are facial flushing and a blocked nose. They can also cause headaches, muscle aches, and indigestion. Sometimes when taking Viagra, men also experience brighter or a blue tinge to their vision.

Most side-effects are not troublesome and only last an hour or so. Most men do not stop taking these PDE5 inhibitors because of the side effects.

It is important to remember that PDE5 inhibitors should not be taken by men who are on Nitrate drugs.

If you are worried about your side-effects or not sure about the safety of taking these drugs in your case, please consult your GP or doctor.

When NOT to take PDE5 inhibitors?

PDE5 inhibitors are NOT to be used with ‘nitrate' drugs, which treat certain forms of heart disease.

PDE5 inhibitors should NOT be used when suffering from unstable heart disease, which should be checked and discussed with your doctor or cardiologist.

When prescribed PDE5 inhibitors, please remember to advise your doctor of other medications you are taking.

Important points you need to know prior to taking PDE5 Inhibitors

  • Trying sexual intercourse too soon or too long after taking a PDE5 inhibitor can influence the drug from working as well as it can:
    • With Viagra and Levitra it takes about 30-50 minutes for the drug to work, and for many men it continues to work for up to 12 hour
    • With Cialis it takes about 2 hours for it to work, but men can still experience erections 24 hours after taking Cialis
  • It is still important to physically stimulate your penis in order for it to become erect
  • Do not eat a fatty meal when taking Viagra, it will affect the drugs from working as well as it can
  • Drinking alcohol can weaken your sexual response
  • A high degree of anxiety can also influence the effectiveness of the drugs


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