I have been using Cialis for a few years and find that if I take it in the AM on an empty stomach it will work , when needed, for about three days. The best thing I use once in awhile is an injection in the penis with Caverject. If used properly an erection is almost instant, works for about two hours and always produces a strong erection. It does not hurt because the penis does not have nerves where the injection is used. There is another injection like Caverject but I can not remember the name.