Hi Moneyboyzz, and welcome to the forum.
I am not myself a niacin user, but those who use it usually need the flush to occur.before ejaculation They use for this doses of 100mg to 300mg, usually. Centrum has around 20mg of niacin per tablets, so that would mean 5 to 15 tablets, which is way too high, because you get all the other ingredients with it as well, and some will be too high in dosage. And, the effect won't be the same, probably, because you have all the other B vitamins with it, so maybe that will interfere with niacin, it is not the same to have only niacin and having all the complex B vitamins at once.
So, no, I do not think this is a viable alternative. It is maybe better to find some niacin tablets, if you really want to give it a try and that your health specialist tells you it is ok for you to try it in safe dosage ( you will understand that nobody on the forum can confirm to you that a product or drug is safe for you, it is your responsibility to check with your health advisor)
