Question: What is the effect of blocking your sperm from coming out when you ejaculate?
Some men try to keep from ejaculating when they orgasm – and I suspect that is what you mean, as I know of no way for a man, in the heat of the moment, to keep just his sperm from coming out during ejaculation.
There’s More To Semen Than Just Sperm
Here’s why: semen is made of several things, including sperm, pre-ejaculator fluids (from the Cowper’s glands), fluid from the seminal vesicles, and fluid from the prostate.
Most of the volume of semen comes from the seminal vesicles and the prostate.
Even though sperm makes up just a small percentage of semen by volume, there are many thousand sperm in every ejaculation. Also, you can’t pick the parts of semen you want and the parts you don’t!
When a man ejaculates, he gets all the parts of semen. So you can’t block the semen from coming out … unless you have a vasectomy, which is a procedure that a doctor can perform that keeps sperm from traveling down the vas deferens tubes to join the rest of the semen.
But If That’s Not What You Mean …
If instead you’re referring to stopping ejaculation but still allowing yourself to orgasm, there is no real harm in that as long as you are not doing anything painful to yourself to try and stop that process.
Some men can just control their ejaculation to stop it, and then have a more intense orgasm later on; some tantric sex practices teach this. They are comfortable doing that and have trained themselves to do that. If you do anything that causes pain, discomfort, bruising, or bleeding, however, then please take care of yourself and check in with a healthcare provider such as a urologist.