Flomax (tamsulosin) and its cousins don't actually shrink the prostate. They relax the smooth muscle tissue at the bladder neck so urine flows easier. The catch: that same smooth muscle exists in your circulation, in ejaculation, and in other places it matters.
The side effects aren't bugs — they're built into how the medication works.
For some men, the tradeoff is fine. For men who are still sexually active and value that part of their life, it can feel like the cure is worse than the disease.