If your doctor finds that you are suffering from low testosterone or if you think that you might be suffering from low testosterone, the main thing you want to know is the cause for your deficiency. Some of the causes can come from a serious disease or condition, such as cancer, that can cause a drop in testosterone output. However, most of the time, Low-T is simply age related. If you are dealing with age-related Low-T, you will want to ask your doctor: