Erectile dysfunction (also known as male impotence) is the inability to achieve or sustain an erection of the penis that is sufficient for sexual intercourse. A 2011 report estimated that 3 million Canadian men over the age of 40 have erectile difficulties. The good news is that there are ways to manage erectile dysfunction.

Medications that are effective in treating erectile dysfunction

There are two classes of medications that are commonly used to treat erectile dysfunction:

  • phosphodiesterase type 5 inhibitors – e.g., sildenafil (Viagra®), tadalafil (Cialis®), and vardenafil (Levitra®)
  • prostaglandin E1 analogues – e.g., alprostadil (Caverject® and Muse®)

The two classes of medications work in different ways. Depending on the cause of the erectile dysfunction, one class of medication may be more appropriate than the other.

Note: All men need to be assessed by a physician before they start taking these medications. The physician will ask a series of questions to ensure that there is no underlying, correctable cause for the erectile dysfunction such as depression, anxiety, or a side effect of a medication. Also, a physical exam will be done. If there are additional sexual problems, such as low sexual desire, blood tests may be needed. It may also be helpful if the partner is seen by the physician.

Phosphodiesterase type 5 inhibitors

How do phosphodiesterase type 5 inhibitors work?
Phosphodiesterase type 5 inhibitors are a class of medications that includes sildenafil (Viagra®), tadalafil (Cialis®), and vardenafil (Levitra®). These medications are taken by mouth and will increase the response of the penis as a man gets sexually excited. For these medications to be effective, the man's nervous system to the penis must be intact. This is because these medications act on one key chemical in the "cascade" of chemicals that are released in the penis, in response to the signal of arousal coming from the man's brain. Therefore, these medications can help produce and maintain an erection only if the man is sexually excited in his mind, and is continually sending signals of arousal down his nervous system. In other words, as long as the feeling of sexual excitement is present, these medications will help the penis become erect by facilitating increased blood flow into it.

Will phosphodiesterase type 5 inhibitors work in men who get erections on their own but, because of psychological issues they have to deal with, have problems getting an erection with their partner?
Psychological issues need to be sorted out and dealt with, whether they relate to work or family, or to the relationship itself. However, at the same time that these issues are being addressed, phosphodiesterase type 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil) may help him focus more fully on positive emotional, and sexual feelings when he's sexually active with his partner. The better he can focus, the more effective these medications will be, and the firmer his penis will be.

Are phosphodiesterase type 5 inhibitors effective in men with diabetes?
Yes, in most cases. In diabetes, the "cascade" of chemicals released by the penis is reduced. However, as long as the sponge-like internal structure of the penis isn't too damaged by poor blood supply, then these medications will be effective in producing an erection in men with diabetes.

What about men with high blood pressure?
Yes, these medications will be effective in most cases.

What about men with conditions of the nervous system, such as Parkinson's disease and multiple sclerosis?
As long as the signal of sexual arousal can get from the brain to the penis, these medications will help produce and maintain an erection.

What about men with spinal cord injury?
If he is able to have partial erections or "reflex" erections from touching his penis, these medications will increase the firmness and duration.

Are there any men who should not take phosphodiesterase type 5 inhibitors?

  • men who are using any form of nitrates (spray, pills, patch), a class of medications that is commonly used for certain heart conditions, such as angina - the combination of a nitrate (e.g., isosorbide dinitrate, isosorbide mononitrate, nitroglycerin) and a phosphodiesterase type 5 inhibitor (e.g., sildenafil, tadalafil, vardenafil) may cause a person's blood pressure to suddenly drop to life-threatening levels where dizziness, fainting spells, a heart attack, or a stroke may occur
  • men for whom sexual activity would be dangerous – especially to their heart
  • men who have a loss of vision in one or both eyes from an eye disease called non-areritic anterior ischemic optic neuropathy (NAION)
  • men who are allergic to any of the phosphodiesterase type 5 inhibitors or any of the other ingredients in the medication
  • men who are using guanylate cyclase stimulators such as riociguat

Men who are taking certain medications for the treatment of HIV (e.g., indinavir, ritonavir) or certain antifungals for the treatment of fungal infections (e.g., itraconazole, ketoconazole) should not use vardenafil (Levitra®).

Should any other men be cautious about taking phosphodiesterase type 5 inhibitors?
Yes, men who:

  • have low blood pressure or uncontrolled high blood pressure
  • are taking an alpha-blocker (e.g., doxazosin, prazosin, terazosin), a medication used to treat prostate problems or high blood pressure
  • have certain heart problems (e.g., coronary artery disease, heart failure, irregular heartbeats, a previous heart attack, unstable angina)
  • have problems in the heart that prevent the flow of blood (e.g., aortic stenosis, idiopathic hypertrophic subaortic stenosis)
  • have certain eye diseases (e.g., retinosa pigmentosa) or have experienced non-arteritic ischemic optic neuropathy (NAION), a condition involving loss of vision due to damage to the optic nerve from insufficient blood supply (ischemia)
  • have anatomical deformities of the penis (angulation, cavernosal fibrosis) or Peyronie's disease, a condition where a layer of scar tissue (plaque) develops under the skin of the penis
  • have had a previous erection that lasted more than 4 hours
  • have liver or kidney problems
  • have had a recent stroke (in the last 6 months)
  • have certain blood disorders (e.g., sickle cell anemia, cancer of the bone marrow, or leukemia)
  • have bleeding disorders
  • have peptic (stomach) ulcers
  • are 65 years of age or over

Prostaglandin E1 analogues

How do prostaglandin E1 analogues work?
Prostaglandin E1 analogues are a class of medication that includes the medication alprostadil (Caverject® and MUSE®). Alprostadil works by mimicking prostaglandin, a chemical in the penis that begins the chemical "cascade" that normally causes an erection due to the signal from the brain. It relaxes the smooth muscle of the penis, allowing more blood to flow into the penis and produce an erection. The advantage of using alprostadil is that this medication bypasses the need for an intact nervous system between the brain and the penis. Alprostadil is either injected directly into the penis using a very fine needle, or is inserted, in the form of a tiny pellet, into the end of the urethra (a tube that carries semen and urine through the penis) at the tip of the penis. Caverject® is the injectable preparation and MUSE® is the pellet form.

So, after injecting or inserting alprostadil, an erection occurs in a few minutes?

Does this mean that the man needs no sexual stimulation to have an erection?
That's right. No stimulation is needed to have a firm penis, but stimulation is certainly needed to enjoy the erection. Stimulation is also very much needed for the man's partner to feel any arousal and pleasure. It's very important that the couple get help from their physician or, if necessary, another therapist to help them adjust to this "instant erection."

Who can benefit from alprostadil?
Because alprostadil is effective without requiring an intact nervous system, it will usually work in men with spinal cord injury or with damaged nerves around the prostate, as well as men with diabetes, high blood pressure, high cholesterol, or coronary artery disease. It will also produce firmer erections in men whose problematic erections result from interfering psychological issues. However, the underlying problems will likely need to be addressed in order for the couple to enjoy the medication-induced erection.

How do men learn these techniques of injection or insertion?
Their doctors will teach them these techniques. This is very important since the information in the packages is often incomplete. For example, when injecting with Caverject®, it's important for the needle to enter the sponge-like tissue of the penis, and the man can be taught to compress the penis so that the injection is accurate. Similarly, for inserting the pellets (MUSE®), there are techniques that a man can learn to reduce any pain and burning in the penis.

Are there safety concerns with injecting alprostadil?
It's important to note that the open wound that results from injecting alprostadil into the penis increases the risk of transmitting or getting sexually transmitted infections because of the direct contact of the wound with bodily fluids. Therefore, it is extremely important to use a latex condom during sexual intercourse.

Are there any men who should not use alprostadil?

  • men who are allergic to alprostadil or to any of the other ingredients in the medication
  • men for whom sexual activity would be dangerous - especially to their heart
  • men who have had a previous erection that lasted more than 4 hours
  • men with sickle cell anemia
  • men with certain cancers (e.g., cancer of the bone marrow or leukemia)
  • men with penile implants
  • men with anatomical deformities of the penis (angulation, fibrosis) or Peyronie's disease, a condition where a layer of scar tissue (plaque) develops under the skin of the penis
  • men with balanitis (inflammation or infection of the glans of the penis) or urethritis (inflammation or infection of the urethra)

Should any other men be cautious about using alprostadil?
Men using blood-thinning medications (e.g., heparin, warfarin) should be careful with injecting alprostadil due to the increased risk of bleeding.

Rosemary Basson, MD
in association with the MediResource Clinical Team 

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.