Erectile Dysfunction (ED)

What is erectile dysfunction?

Erectile dysfunction is a common problem of not being able to get and keep an erection or hard on for long enough. It is generally defined as the inability to to get or keep an erection sufficient for sex.


How does a normal erection work?

The penis is made up of two erection cylinders (copora cavernosa) and the tube urine passes through (the urethra).  The erection cylinders have vascular spaces inside them that can fill up with blood. During a normal erection blood flow into the penis is increased and blood flow out is decreased. This makes the penis swell. The swelling in turn pinches off the blood flow out and a positive feed back loop occurs. After ejaculation the blood flow in decreases and this causes the blood flow out to increase so the penis deflates.

More blood in + less blood out = an erection

What causes erectile dysfunction?

ED can have many causes. The most common is aging. As we age the risk of ED increases. Any conditions or diseases that cause problems with blood flow in or increased blood flow out or damage to the nerves that cause an erection will make it harder to get erections. Common causes for ED are

  • Smoking
  • Diabetes
  • High blood pressure
  • Excess alcohol consumption.
  • Surgery

Smoking and diabetes are 2 common causes of ED

Less common problems include low testosterone, low thyroid function, stress and tiredness. Occasionally bike riding can alter erections. ED can cause stress and relationship issues, as well as being the consequence of these.


How common is ED?

ED is surprisingly common, how else would Viagra have made billions for its owner. ED becomes more common as we age. Maybe half of all men in their 50’s have had some problem sometime with an erection. By age 65 at least 25% men suffer from ED.

What tests do I need?

Typically, you will need a few blood tests. These are to check your testosterone level, blood sugar level and thyroid function.

How can I treat ED?

Since the advent of Viagra some 10 years ago the treatment of ED has become much easier. Treatment is divided into

  • Counselling
  • Pills such as Viagra/Avigra
  • Injections into the penis
  • Vacuum device
  • Penile implant or prosthesis

How does Viagra work?

When a blood vessel needs to dilate or get bigger the brain tells the smooth muscles around the blood vessel to relax. This is done by sending a message down a nerve, which causes a series of chemicals to be released, the end result of this is for the calcium levels in the muscle cells to change.

Specifically, the nerve ending   releases a chemical called Nitric Oxide (NO). NO passes into the smooth muscle cells of the blood vessel wall and in turn tells an enzyme in the muscle cell to make a chemical called cGMP.  cGMP then ultimately leads to a decrease in calcium levels in the cell. This fall in calcium level causes the muscle cells to relax.



When the muscle cells relax the blood vessel stretches and allows more blood flow. The process is controlled by the brain switching on and off the nerves, and by an enzyme breaking down the cGMP. This enzyme is called PDE, and is the same in all blood vessels.  In the penis the particular enzyme that does this job is called PDE5 and it is this enzyme that Viagra blocks.

So if we block PDE5 the cGMP made will hang around for longer, this will lead to more calcium in and so gives a stronger message to the blood vessel to relax. In the end this means more blood flow for longer and so a better erection.



The process is not automatic. You need to be sexually aroused to release the NO. If there are no nerves this cannot happen. If you are not sexually aroused this cannot happen.  Viagra is therefore not an aphrodisiac, but augments the response that is already there.

What is the difference between Viagra and Cialis?

Viagra (sildenafil) was the first PDE5 inhibitor made. It takes about an hour to work and the benefit lasts for up to 5 hours. Cialis (tadalafil) differs from Viagra in that it has a much longer half life. This means that a tablet of Cialis can have an effect for up to 24 hours after taking.  It is best to take Viagra or Cialis on an empty stomach as food decreases the amount absorbed. Levitra a third PDE5 inhibitor is similar to Viagra but has a quicker onset and is not so affected by food.

Viagra is now off patent so generic copies are available, such as Avigra or Silvasta at about $8 a pill. Since October 2015 they have become available without a prescription in NZ. Cialis and Levitra are both still on patent, but these are due to expire soon. When that happens they both should be much cheaper and available over the counter.

Sildenafil (Viagra) tends to give stronger erections than Tadalafil (Cialis). Many couples struggle with the time demand of sildenafil and prefer the longer time frame that tadalafil (Cialis) allows. Levitra (vardenafil) never got a large following in NZ.

What are the side effects of Viagra or similar drugs?

These drugs all act by making the blood vessels in the penis dilate or get bigger. They all cause to some extent other blood vessels to stretch, and differ slightly where this effect is strongest. Sildenafil (Viagra) often causes a facial flushing.

How do I know my ED is not just in my head?

Sometimes ED is “in the head”. If you wake with erections in the morning, but cannot get erections when you want to have stress, then the problem is psychological. If, however you have stopped waking with morning erections then the problem is not in your head and the problem is either in the plumbing or the nerves supplying the penis. This is the most common reason.

The standard line is “you are only as good as your last erection”. By that we mean that if you had problems last time with an erection, then the next time you go to have sex, a tiny bit of stress will creep in. This leads to a little bit of adrenaline and that causes the blood vessels supplying the penis to shut down. Nothing you can do about it really. If that might be the problem, then Cialis 5mg daily might help.

I think a pill my doctor gave me may have caused the problem.

Sometimes pills for high blood pressure can affect your erections. Sometimes pills for peeing problems can make erections worse (hytrin, doxazosin). Finasteride, which is used to shrink the prostate in men who have trouble peeing, can decrease sexual desire (libido). After stopping the drug, it can take several months for libido to recover.

Viagra doesn’t work for me, what else can I try?

If sildenafil (the proper name for Viagra/Avigra/Silvasta etc.) does not work, then it maybe worth trying Cialis. In NZ the problem is that sildenafil is off patent, while Cialis is not, this makes Cialis very expensive. Having said that it maybe worth trialling either a month of Cialis 5mg/day or 20mg on demand.

If neither Viagra or Cialis is effective, then the next options are

  • Penile injections
  • Vacuum device
  • Penile prosthesis

How do penile injections work?

Penile injections are drugs that cause the blood vessels in the penis to dilate or increase in size.  The commonest injection is a chemical called caverject. Caverject is a form of prostaglandin. Prostaglandins directly cause the release of cGMP, which in turn change the calcium levels in the muscle cells of the blood vessel. This causes the blood vessels to stretch. More blood in =an erection. It is independent of the erection nerves and works even if they have been cut or removed.

The injection is put into the penis as shown below.  You should draw up a small amount from the vial into the syringe and then this is injected into the penis. The amount injected is increased slowly until the amount produces a hard erection that lasts for ½ to 1 hour.  The injection is into the penis between 1 and 3 o’clock, and 9 and 11 o’clock. You only need to inject one side as the chemical passes from one side to other.

Is there any risk of using injections?

Yes, the major risk of using an injection is an erection which does not go down again. If this lasts for hours and hours, then the blood flow into the penis becomes stagnant and the tissues suffer from a lack of oxygen. A prolonged erection such as this is called a priapism.

Other risks are bruising at the site of the erection and pain. Often when the penis has not had an erection for some time the first few erections can be sore, possibly as the tissues stretch again. Caverject tends to be more sore when used in the first 3 months after surgery, than latter. This is due to the caverject binding to what are called p-receptors in the penile tissue. P-receptors modulate pain and are increased in the first 6 weeks to 3 months after surgery.

What should I do if I get a priapism (prolonged erection)?

If you have injected yourself and the erection ahs lasted longer than 2 hours then you should take 2 pseudoephedrine pills (Sudafed).Repeat the dose at 4 and 6 hours, if the erection continues. Make sure you have ejaculated. IF despite this and the pills it continues then sometimes riding a bike will help compress the blood vessels feeding the penis and so help the erection to go.

If the erection has not gone down after 4 hours and 2 x 2 Sudafed pills, then you should call your urologist. He/she will organise to arrange drainage of blood from the penis and may inject an antidote, such as adrenaline to make the blood vessels shrink.

Why am I not getting an erection even though I have used an injection?

There are three possible reasons.


  1. The dose you are using is not big enough.
  2. So slowly increase the amount of drug used each time.
  3. If after using a full syringe you are still not getting a fully hard erection, then you may need a second or third type of drug added to the injection mixture.
  4. Blood is leaking back out of the penis. This is called a venous leak.  So although lots of blood is pumping into the penis it leaks back out again.
  5. One way to fix this is to use a penile or cox ring to pinch the base of the penis slightly. These can be purchased from any sex shop. Although there are many many types and shapes, a tightish simple ring is probably the best.
  6. It is believed that the leaks are more likely to occur in men who have not had erections for some time after say surgery. One of the hopes is that if you use injections early after surgery then you are less likely to get a venous leak.
  7. You are injecting the wrong place.
  8. Make sure the injection is into the main body of the penis. Avoid injecting the midline of the penis or the urethra.



I don’t want to use injections, how does a vacuum pump work?

Vacuum pumps work by sucking blood into the penis. Once the penis is erect a very tight rubber band is placed over the base of the penis to hold blood in. The advantage of a vacuum pump is that no injection is needed. The disadvantage is that the erection is “cold” rather than hot.

A second use of vacuum pumps can be to reduce the penile shrinkage that happens after surgery if erections are not taking place.



A vacuum pump can be purchased in NZ form 2 different companies, or bought online through sites such as  If you use they will not ship the pump to NZ directly, so you need to use a Youshop or similar mailing address to get it to NZ


What is a penile prosthesis?


A penile prosthesis is 2 hydraulic cylinders that are placed into the body of the penis itself.  This are connected to a control pump in the scrotum and a reservoir in the body. Squeezing the control pump pushes fluid into the cylinders which distend and become hard aka produce an erection. The fluid slowly bleeds back into the reservoir over time.

Most men who have a prosthesis fitted are very happy with the outcome, it is not publically funded in NZ and costs around NZ $30,000 for the device and the surgery needed. Some insurance companies may pay for it.

I don’t like any of the options for erections what else can I do?

If all of the above seems to foreign or too clinical then the most important thing to remember in any sexual relationship is your relationship with your partner. So rather than having vaginal penetration with an erect penis, you can as a couple choose other options. These range form just having cuddles to erotic massage or oral sex. The choice is yours and your partners.

Many men are happy to know that they can get an erection (by pills, injection or pump), and are happy not to use them but continue on in a loving and/or sexual relationship without paradoxically having sex.

Where can I find more information on ED?


For a very in depth discussion on ED see

For a discussion on injection therapy and issues around it

For a discussion on how Viagra works see

for how a vacuum pump works

For a discussion on penile prosthesis