Causes of ED

Mechanism of Erection

Penile erection is managed by two different mechanisms: The first one is reflex erection, which is achieved by directly touching the penile shaft. The second is psychogenic erection, which is achieved by erotic or emotional stimuli. The former uses the peripheral nerves and the lower parts of the spinal cord, whereas the latter uses the limbic system of the brain. In both conditions, an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system leads to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy erectile system. Based on the mechanism of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply or psychological problems. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease.

Nerve Signal Pathway of Erection: 

Source: National Institute of Diabetes and Digestive and Kidney Diseases

Anatomy of the Penis: 

Structural Changes of the Penis before and after Erection: 

Insufficient rigidity / erectile dysfunction is caused by physiological or psychological factors, or both.

About 80-90% of cases of insufficient rigidity / ED are caused by physiological origin, which are further classified into vascular (related to blood flow) and non-vascular factors. It is estimated that 70% of insufficient rigidity / ED cases may be attributable to vascular diseases alone.

A penis requires a healthy blood supply in order to erect. Even only a minor obstruction will lead to a serious erection problem. This is described as the lack of adequate penile blood supply, which is a result from the following factors:

Source: The National Institute of Diabetes and Digestive and Kidney Diseases

Common Physiological Risk Factors

  • Diabetes
  • Hypertension
  • High Blood Cholesterol
  • Cardiac Diseases
  • Smoking
  • Prostatitis

Poor Overall Circulation: 

Arterial Blood Vessels of the Penis: 


Type 2 Diabetes mellitus occurs when the pancreas does not make enough insulin, or when body tissues cannot utilize insulin effciently, resulting in an abnormally high blood glucose level.

Advancing thirst, tiredness, weight loss, blurred vision and others are symptoms of diabetes. The condition will also lead to insufficient rigidity / erectile dysfunction by inducing damages of blood vessels and nerves involved in erection.


Hypertension is a condition in which the blood pressure is persistently higher than normal (140/90 mmHg), even when you are resting or relaxing.

Smoking, physical inactivity, obesity, stress, excess alcohol intake and a family history of hypertension are risk factors of hypertension. Most people with hypertension do not have any symptoms. According to the Population Health Survey of the Department of Health, 60% of males with hypertension do not know they have the disease. Hypertension is usually diagnosed unexpectedly in a routine health check-up. When severe, hypertension will cause headache, dizziness, and visual problems. Impotence is also one of the symptoms of hypertension. It is because penile arteries are damaged by excessive blood pressure. Normally, these arteries dilate in response to sexual stimulation, allowing more blood to flow into the spongy tissue of the penis to produce an erection. The excessive pressure in these arteries may cause tiny tears, which are subsequently repaired by the body. The healed arteries have thicker walls to better resist the elevated blood pressure. These thicker blood vessel walls, though, will impose extra resistance to blood flow into the erectile tissues of the penis.

Cardiac Disease

Cardiac Disease is one of the main killer diseases among men in Hong Kong, causing 3,442 deaths in 2008. Coronary heart disease accounted for approximately two thirds of all heart-disease-related deaths in men.

Coronary heart disease (CHD) is a type of heart disease due to the occlusion of the coronary arteries. The coronary arteries serve to supply oxygen and nutrients to the heart muscles. When the arteries become narrow and stiff because of fatty plaques, blood supply to the heart will be reduced and the heart muscles will be damaged.  

A number of risk factors, including smoking, high-fat diet, physical inactivity, high blood pressure, high cholesterol levels, obesity, diabetes mellitus, stress and family history of coronary heart disease, which may work independently or in combinations, can lead to coronary heart disease.  


Smoking is associated with insufficient rigidity / erectile dysfunction by damaging the blood circulation system in the penis. As insufficient rigidity / ED is shown to be highly prevalent among smokers in clinical studies, it is hypothesized that quitting smoking can help prevent insufficient rigidity / ED, and improve the condition in insufficient rigidity / ED patients.


Prostatitis is an inflammation of the prostate gland. It can be sudden and acute, or reoccurring and chronic. This disease is often accompanied by a strong and frequent urge to urinate, difficulty in urinating (hesitant urination often results in only small amount of urine), and / or pain in the lower back or abdomen. Prostatitis can also cause insufficient rigidity / erectile dysfunction due to reduced blood flow.

Other Possible Physical Factors

Other associated physical conditions or causes are less common. These include:

Neurogenic DisordersSpinal cord and brain injuries, nerve disorders such as Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, and stroke.
Hormonal DisordersPituitary gland tumor; low level of the hormone testosterone.
Cavernous DisordersPeyronie’s disease.
Metabolic SyndromeCharacterized by belly fat, high unhealthy cholesterol and triglyceride levels, high blood pressure, and insulin resistance.
SurgeryRadiation therapy, surgery of the colon, prostate, bladder, which may damage the nerves and blood vessels involved in erection.
Medication CausedVarious antihypertensives (medications intended to control high blood pressure) and some drugs that modify central nervous system response may inhibit erection by denying blood supply or by altering nerve activity.
ObesityMen who are obese are much more likely to have insufficient rigidity / erectile dysfunction than men with a normal weight.

Since insufficient rigidity / erectile dysfunction can be an early symptom of such underlying medical conditions, it is essential for patients to seek prompt diagnosis and treatment.

It is however, not uncommon to see insufficient rigidity / ED in an otherwise completely healthy person, both physically and psychologically. It is postulated that the penile circulation is intrinsically precarious, being an end-artery it may not be surprising that blood flow to the penis be partially occluded as men age. Although this may not cause major health problems, erection problems may arise due to the hindered penile blood flow.

Possible Psychological Factors

Psychological factors are responsible for about 10%-20% of all cases of insufficient rigidity / ED. It is often secondary to an underlying physical cause. In some cases, the psychological effects of insufficient rigidity / ED may stem from childhood abuse or sexual trauma. However, the most common psychological causes of insufficient rigidity / ED include: 

StressStress can be job-related, money-related, or the result of marital problems, among other factors.
AnxietyOnce a man experiences unsatisfactory erection, he may become overly worried that the problem will happen again. This can lead to “performance anxiety”, or a fear of sexual failure, which contributes to the consistent insufficient rigidity / ED.
Guilt / Low self-esteemA man may feel guilty that he is not satisfying his partner.
DepressionA common cause of insufficient rigidity / ED, depression affects a person physically and psychologically. Depression can cause insufficient rigidity / ED even when a man is completely comfortable in sexual situations. Drugs used to treat depression may also cause insufficient rigidity / ED.
IndifferenceThis may come as a result of age and subsequent loss of interest in sex.

The Characteristics of Psychological Insufficient Rigidity / Erectile Dysfunction Include:

  • Being able to achieve or maintain an erection with one partner but not with another.
  • Having strong and lasting erections in the mornings and during masturbation but not during love making.
  • Tendency to affect younger men with unstable relationships or unsettling past experiences.

Other Possibilities That Cause Insufficient Rigidity / ED

A variety of risk factors can contribute to insufficient rigidity / erectile dysfunction. They include: 

Getting OlderAs many as 80% of men aged 75 and older have insufficient rigidity / erectile dysfunction. Erections may take longer to achieve, may not be as rigid or may take more direct touch to the penis to occur. But insufficient rigidity/erectile dysfunction isn’t an inevitable consequence of normal aging. Insufficient rigidity / erectile dysfunction often occurs in older men mainly because they’re more likely to have underlying health conditions or take medications that interfere with erectile function.
Substance AbuseChronic use of alcohol, marijuana or other drugs often causes insufficient rigidity/erectile dysfunction and decreased sexual drive.
Prolonged BicyclingOver an extended period, pressure from a bicycle seat has been shown to compress nerves and blood vessels supplying the penis, leading to temporary insufficient rigidity / erectile dysfunction and penile numbness.
Understanding Erectile Dysfunction

Insufficient rigidity / erectile dysfunction (ED) is defined as the inability to achieve an erection or maintain an erection sufficient for satisfactory sexual intercourse.

Insufficient rigidity / ED is a very common medical condition with significant consequences. The average age of disease onset is 50 years and the prevalence increases with age.

However, any man at any age can also be affected by insufficient rigidity / ED – patients as young as 18-year old have been recorded.

According to Hong Kong Men’s Aging Research Association, there are currently 152 million men who are affected by insufficient rigidity / ED worldwide. In October 2003, a survey, conducted by the Hong Kong Urological Association, revealed that 62 percent out of 654 men, aged between 40 and 79, suffered from some degree of insufficient rigidity / ED. Based on this survey result, the number of men who are currently affected by insufficient rigidity / ED in Hong Kong is estimated to be at a staggering 910,000.

Atherosclerosis alone accounts for 50% to 60% of insufficient rigidity / ED cases in men aged 60 years and older. Insufficient rigidity / ED is present between 35% and 50% of men with diabetes. Insufficient rigidity / ED may also be a predictor for other vascular problems.

Possible Signs of Insufficient Rigidity / ED:

  • Difficulty in achieving or maintaining an erection at least once in every four times of attempting sexual intercourse, or persisting for more than one month.
  • Needing longer time than usual to achieve an erection.
  • Erection becomes weaker or less rigid.
  • Morning erection becomes less frequent or less rigid.
  • Climaxing or ejaculating sooner, or with an incomplete erection.

Insufficient rigidity / erectile dysfunction has profound impact on a person’s quality of life. It does not only mean a loss of sexual satisfaction, but it also creates adverse effects on intimate relationships. The inability to have sex makes someone suffering from it feel inferior or unmanly. This may also lead to social inhibition and poor self-image. Instead of finding cure to the problem, most people try to cover up their conditions. They may avoid sexual contact with their partners and this leads to marriage breakdown eventually.  

If you have such problem, you should not hesitate to consult a doctor immediately. To discuss your problem with your partner and gain her support are also important as her involvement would definitely help during the progress of treatment.

When to Seek Medical Help?

All men at one time or another will experience insufficient rigidity / ED. If the problem becomes persistent — occurs more than 25% of the time and lasts for more than 2 months, or becomes a source of distress for you or your partners, you should seek medical assistance. The sooner it is diagnosed and treated, the better the outcome because:

  • early identification and correction of the underlying problems (can be physically or psychologically) can prevent further deterioration.
  • the earlier insufficient rigidity / ED treatment is started, the better the opportunity for an effective treatment plan to restore healthy blood flow to the penis and spontaneous erection.
  • a healthy sex life can contribute to healthy self-esteem, self confidence, better relationships, and satisfaction in many other aspects of life, including social, family and work environments.

The ultimate goal of the Insufficient rigidity / erectile dysfunction treatment is to help both patients and their partners to regain sexual satisfaction. We focus on a curative approach rather than just treating patients’ symptoms. This way, patients do not have to rely on life-long medications when dealing with such problem. There are numerous ways to treat ED, some common and effective methods include Mixture Therapy, Oral Medication and Counseling (Sex Therapy)

1) Mixture Therapy

Mixture Therapy was first introduced in early 1980s and has been widely used by doctors around the USA, Europe, Latin America, Australia for decades. In Hong Kong, the therapy has been practiced by doctors since 2004. The efficacy and tolerability of Mixture Therapy is clinically proven by hospitals and universities worldwide.

Unlike the over-the-counter-drugs, Mixture Therapy is required to be prescribed by a registered doctor. To determine the most suitable dosage, the doctor will conduct relevant tests to evaluate patients’ blood flows and the nerve systems.

Details on Mixture Therapy:Mixture Therapy

2) Oral Medication

Oral medication is the most common and convenient treatment option for patients. Common oral medications for insufficient rigidity / erectile dysfunction belong to a class of drugs called selective enzyme inhibitors which block the enzyme phosphodiesterase-5 (PDE5). Blocking this enzyme helps maintain levels of cyclic guanosine monophosphate (cGMP), a chemical produced in the penis during sexual arousal. Balanced levels of cGMP causes the smooth muscles of the penis to relax and increases blood flow.

Details on Oral Medication for Premature Ejaculation: Oral Medication

3) Lifestyle Changes

Lifestyle of any individuals should be assessed for any potential risk for insufficient rigidity / ED. Doing more exercises, quit smoking, losing weight, and cutting back on alcohol help solve erection problems to some extent in some patients.