I also take it twice a day - but not at exactly the same time. It takes about
5 days before I feel missing it...a dose here and there, I'm okay....but, if I miss a dose 'here and there' a LOT....it does catch up with me after a while. Then, when I start taking it regularly again, I have to go through all the tummy troubles readjusting to a full dose again for a few days.
I do take a super B complex every morning as well.....if I miss a lot of that, my fatigue increases.