Sildenafil works by preventing the action of a chemical in the body called phosphodiesterase type 5. This helps to relax (widen) blood vessels and improves the flow of blood. In erectile dysfunction, Sildenafil improves the blood flow to the penis following sexual stimulation, and this helps to maintain an erection.
Sildenafil is available on prescription. Do not take it if you do not have erectile dysfunction.
Another brand of Sildenafil tablets called Revatio is used in a completely different condition called pulmonary arterial hypertension. This is a specialist treatment and no information about this brand of Sildenafil is included in this medicine leaflet. Most men have occasional times when they cannot get an erection. For example, you may not get an erection so easily if you are tired, stressed, distracted, or have drunk too much alcohol. For most men it is only temporary, and an erection occurs most times when you are sexually aroused.
However, some men have persistent, or recurring, ED. It can occur at any age, but becomes more common with increasing age. About half of men between the ages of 40 and 70 have ED. About 7 in 10 men aged 70 and above have ED.
When you are sexually aroused, messages from your brain travel down nerves to your penis. Chemicals called neurotransmitters are then released from the ends of the nerves in the penis. Stimulation of the penis can also cause local nerve endings to release neurotransmitter chemicals.
The neurotransmitters which are released in the penis cause another chemical to be made, called cyclic guanosine monophosphate (cGMP). This chemical causes the arteries in the penis to widen (dilate). This allows extra blood to flood into the penis. The rapid inflow of blood causes the penis to swell into an erection. The swollen inner part of the penis also presses on the veins nearer to the skin surface of the penis. These veins normally drain the penis of blood. So, the flow of blood out of the penis is also restricted, which enhances the erection.
Once you stop having sex, the level of cGMP falls, the blood flow to the penis returns to normal, and the penis gradually returns to the non-erect state.
There are several causes which tend to be grouped into those that are mainly physical and those that are mainly due to mental health (psychological). About 8 in 10 cases of ED are due to a physical cause.
Reduced blood flow to the penis. This is, by far, the most common cause of ED in men over the age of 40. Like in other parts of the body, the arteries which take blood to the penis can become narrowed. The blood flow may then not be enough to cause an erection. Risk factors can increase your chance of narrowing of the arteries. These include getting older; high blood pressure; high cholesterol; smoking.
Diseases which affect the nerves going to the penis. For example, multiple sclerosis, a stroke, Parkinson's disease, etc.
Diabetes. This is one of the most common causes of ED. Diabetes can affect blood vessels and nerves.
Hormonal causes. For example, a lack of a hormone called testosterone which is made in the testes. This is uncommon. However, one cause of a lack of testosterone that is worth highlighting is a previous head injury. A head injury can sometimes affect the function of the pituitary gland in the brain. The pituitary gland makes a hormone that stimulates the testis to make testosterone. So, although it may not at first seem connected, a previous head injury can in fact lead to ED. Other symptoms of a low testosterone level include a reduced sex drive (libido) and changes in mood.
Injury to the nerves going to the penis. For example, spinal injury, following surgery to nearby structures, fractured pelvis, radiotherapy to the genital area, etc.
Side-effect of certain medicines. The most common are some antidepressants; beta-blockers such as propranolol, atenolol, etc; some 'water tablets' (diuretics); cimetidine. Many other less commonly used tablets sometimes cause ED.
Alcohol and drug abuse.
Cycling. ED after long-distance cycling is thought to be common. It is probably due to pressure on the nerves going to the penis, from sitting on the saddle for long periods. This may affect the function of the nerve after the ride.
Excessive outflow of blood from the penis through the veins (venous leak). This is rare but can be caused by various conditions of the penis.
In most cases due to physical causes (apart from injury or after surgery), the ED tends to develop slowly. So, you may have intermittent or partial ED for a while, which may gradually get worse. If the ED is due to a physical cause, you are likely still to have a normal sex drive apart from if the cause is due to a hormone problem. In some cases, ED causes poor self-esteem, anxiety, and even depression. These reactions to ED can make the problem worse.