I took zoloft for awhile and definitely remember numbness in the penis, but it was different. There was some tingling when erect, and erections were just as hard. It did take longer to reach orgasm, but there was no weakening of the ejaculation, as far as I could remember.
Some speculated that the mind was affecting libido and erections, considering that zoloft is an SSRI antidepressant, that it’s main target is the mind, and maybe the signals from the brain to the penis are interrupted. From what I can sense with my own fin side effects, this is not the case. I can feel the signals hitting that area, and things are trying to respond, but can’t.