Seems to work well in patient's where there is a medical reason for lack of, or lack of maintenance of erection (erectyle dysfunction).
Not so good if your reasons for the problem are not medical.
Has to be used with caution if you have certain conditions affecting the heart, or blood vessels.
Can have some side effects, including heartburn, vomitting, dizziness, but then again, so does 8pints of stella and a curry. (My own personal remedy)