PDE5 Inhibitors

What are PDE5 Inhibitors?

PDE5 Inhibitors are a class of medicines used to treat Erectile Dysfunction.

There are 3 brands currently available. They are Levitra, Cialis and Viagra.

How do PDE5 Inhibitors work?

As the name suggest, PDE5 Inhibitors inhibit an enzyme called Phosphodiesterase-5 (PDE5).

During sexual stimulation, the body produces a chemical called cGMP (Cyclic Guanosine Monophosphate). cGMP causes the blood vessels in the penis to dilate thereby increasing blood flow to the penis and causing an erection. cGMP is broken down by PDE5. By blocking the PDE5, the level of cGMP in the penis increases and the blood vessels dilate more leading to a better erection.

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What is the difference between the 3 PDE5 Inhibitors?

Viagra was the first PDE5 Inhibitor to be introduced. It is reported to cause the best hardness. It is also used to treat Pulmonary Hypertension. It comes in doses of 50mg and 100mg.

Viagra now comes in a new kind of tablet that melts in your mouth. It is called the Viagra Melt Tabs or ODT. Click here for more info. 

Cialis was the second PDE5 Inhibitor to be introduced. It has the longest duration of effect; up to 36 hours. Latest studies show that taking 5mg everyday has the same effect of taking 20mg before sex. This dosing schedule has the added benefit of improving the health of the inner lining (endothelium) of the blood vessels. It also disassociates the act of taking the pill and sex. Financially it is also beneficial for people who take 2 or more pills of 20mg a week.

Levitra is the third PDE5 Inhibitor to be introduced. It has the fastest onset; as little as 15 minutes and is reported to be the most potent. It is shown to be effective in people who have undergone Prostate Surgery or are suffering from chronic diseases such as Diabetes.

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What are the side effects of PDE5 Inhibitors?

PDE5 Inhibitors all can potentially cause flushing, heartburn and headaches. Viagra can cause visual disturbances.

What are the dangers of PDE5 Inhibitors?

PDE5 Inhibitors must not be taken with any medicines that contain Nitrates. Please check with your Doctor before taking any PDE5 Inhibitors.

Do not take more than the prescribed dose.

Beware of counterfeit drugs. PDE5 Inhibitors are prescription drugs that can only be obtained from your Doctor. Do not buy drugs from an unlicensed source.

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Related Topics:

Testosterone Deficiency / Andropause

Erectile Dysfunction

Premature Ejaculation

Pearly Penile Papules

About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.

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  1. There is any new med biside livitra cieles or viajra injection better for ed in diabetes

    • You can try ESWT. It is a new treatment where shock waves are passed into the penis to improve blood flow. Click HERE for more info.

  2. What causes the pde5 inhibitor enzyme and are there any natural ways to stop it from interfering with erections other than the three well known medication. Is there a natural way to inhibit the pde5 enzyme. Thank you for your time

    • Phospho-Diesterase is a heterogenous family of naturally occurring enzymes in the body. They serve to cleave the phosphor-diester bond in cAMP and cGMP and plays a key role in the second messenger signal transduction pathway. They do not cause ED. What the PDE5I medicines do is block this enzyme which results in an increase in Nitric Oxide which leads to relaxation of the vascular smooth muscles. What causes ED is blockage of the vessels and unhealthiness of the inner lining of the vessel walls. To reverse this, we prescribe a healthy lifestyle of diet rich in fruits and vegetables and regular exercise.

  3. for some reason found viagra of little use except to cause head ache bit the other two pde5 inhibitord very effective

    • drtan

      Thank you for your feedback. Headache is a common side effect that is associated with all 3 PDE5Is.


  1. Electro Shock Wave Treatment (ESWT) for ED | Men's Health - […] cases of ED where the patient could not get an erection even with medicines for their ED (i.e. PDE5…
  2. Testosterone and Erectile Dysfunction (ED) | Men's Health - […] most popular treatments for ED are the PDE5 Inhibitors. There are currently 3 brands available, Levitra, Cialis and […]
  3. Erectile Dysfunction (ED) | Men's Health - […] There are many treatment options currently available for erectile dysfunction. The most popular are the medications known as PDE5…
  4. The Low Down on Viagra, Cialis and Levitra | Men's Health - […] is one of a group of medicines known as PDE5-inhibitors (so named because they inhibit an enzyme called PDE5).…

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