Alright, so my results so far are so good that I needed to post them. I guess I'm one of the rare few that was able to get the niacin to work taking it after ejaculation. Me an my lady are having a hard time timing it right to take it before hand on any empty stomach, but 2 times it's worked taking it after on an empty or mostly empty stomach.
The first time was about 2 weeks ago. I felt the horrible onset of POIS and the next day I couldn't move, severe depression and my OCD symptoms were out of control. I took the niacin during that agony, had the flush and all of the physical and mental disappeared within an hour.
The second time was last night. I took it immediately afterword and no POIS symptoms and trust me I get POIS every time with or without O. This is not placebo, I am a very skeptical person. All I felt afterwords was a real nice relaxation, probably what normal people feel after having sex. I normally get the kind of POIS that leaves you in bed for 5 days with severe fatigue and depression. The kind that makes you want to end your life, amongst a plethora of other horrible POIS symptoms. This has been going on for about 20 years, getting worse every year.
I know it's still too early to say it's 100%, but it was a huge relief for me, and it might encourage someone who has yet to try it or if it failed taking it before hand. I'll keep posting my results on this thread. I think the key is to definitely take it on an empty stomach to get the flushing effect.