I unfortunately posted this in the product/vendor forum, but I'll post it here again as this seems to be the relevant forum:
I've been taking NR/Niagen since the beginning of August 2016. It changed my life in terms of energy levels and stamina. I feel like I'm 18 again (42 years old). I'm not even exaggerating. I did notice a decrease in erections a few months into it (I didn't have sex until a few months into it) where I had a hard time keeping it hard in a condom and also hard when "out" for even short amounts of time (change positions etc.) and attempts to get it back in required herculean effort or failed. But somehow it still worked even at reduced hardness and I still had a sex drive...although reduced. That was when I was taking 250mg of NR a day. About a month ago I started taking 500mg of NR. In the last two weeks I had two sexual encounters and both times I could not even get an erection much less have sex. I also notice that I don't even have a sex drive...it's gone. The only change I made was to take double the amount of NR.
Here's my question..since research into NR is sparse and also user experiences are relatively sparse, did you notice anything similar? I found one post here from 2014 that reported ED issues...but that seems to be about it. If ED and lack of or low libido is a common side effect of NR, then it's going to be a hard sell commercially. Anyone?
And this is my reply to someone with more information:
The most recent episode (after increasing to 500mg) is with the same partner. It's even hard to masturbate at this point, nor do I have the desire. This has NEVER happened to me before. I do take my normal vitamins, but not in crazy amounts (just what it says on the bottle) and I have been taking those for over a decade. So no changes there. As for the amazon reviewer...he says: "I think" behind increased libido. I do remember at the very beginning thinking that I was hornier, too, but that may be either real or placebo in the beginning due to the increased energy levels.
What I did find out in my research is that Niacin is used in place of cholesterol lowering drugs (statins) for a similar cholesterol lowering effect. If you don't have high cholesterol (and I don't..i'm normal weight, active, fit, healthy with no known problems) than Niacin (and Statins) may lower your cholesterol too much. Niacin and NR are both "Vitamin B3"..i.e. very, very similar. I found at least one source that described NR as cholesterol lowering and I *think* I read on here that some people with high cholesterol reported their values improving...i.e. going down.
Why is cholesterol important to this topic? Well, cholesterol and testosterone are structurally very similar and cholesterol is needed by the body to synthesize testosterone. I'm deducting/speculating that if there isn't enough cholesterol to go around that testosterone production will be insufficient. That would explain the lower levels of libido/erection in the beginning and the total loss of libido/erections after increasing my NR intake to 500mg/day.
Starting today I am going to stop taking NR and see if I notice any improvements in the next days and weeks.