Talk to Andrologist on Erectile Dysfunction

I am facing ED and do not get morning erection. Also, not able to sustain erection for a sufficent time and have weak erection. As per doctor prescription, I have used cialis 1/4 daily for a period of two months but couldn't achieve satisfactory results. However, doctor advised me to increase cialis dose to half or full and then determine whether it gives desired erection and if it is ok then use it for rest of your life. My question is , whether it is safe to use it for a longer period?? Or any other treatment suggestion pls?