Does stopping ejaculation flow cause harmful effects to the body?

Would the pill still work if u had sex when on ur peried?

That's what happens when you get a vasectomy. After cutting it they clamp the tube so it can't get out. I asked the doc about it getting forced back into my balls and he said the body just absorbs it. It felt kind of funny at first just like it was being shoved back into my balls (say what?) but that feeling went away in time and it just felt normal.

I assume you are talking about pinching your penis to accomplish it. I used to do that to give me time to pull out before letting it loose. I had no ill effects except for a soreness from the pinching. When I was a teen we used to do it when we had contests for distance. It gave you a better more forceful shot when you let it go.