Viagra has many side effects on the body and so only to be taken if erectile dysfunction is present and that too under proper doctor's supervision.

It depends on the cause of erection issue. In general; good balanced diet, regular exercise, normal BMI, no smoking or alcohol, adequate sleep and control of mental stress will help.

Some tests can be done to know if there is any organic or physical cause and also detailed history including psychological evaluation helps.

It's mostly based on history of symptoms such as trouble getting an erection, trouble keeping an erection and reduced sexual desire. Tests are done to know the presence of any organic causes.