Inclusion Criteria:  Male heterosexual patients aged 22-70 years. Confirmed clinical diagnosis of mild, moderate or severe ED for more than 3 months. Involved in a continuous heterosexual relationship with their partner for at least 6 months.  Exclusion Criteria:  Any significant cardiovascular, pulmonary, hepatic, renal, gastrointestinal, haematological, endocrinological, metabolic, neurological or psychiatric disease. History of unstable medical or psychiatric condition or using any medication that, in the opinion of the Principal Investigator, is likely to affect the patient's ability to complete the investigation or precludes the patient's participation in the investigation.