I have been on a low carb diet for a couple months now, this being the third time doing the low carb way of life. However, this is the first time I've experienced what is called the "Low Carb Flu"... I had felt very "drained", lethargic, headaches etc... So between this vitamin and stepping up the amount of water I drink... the "Flu" went away. I only take 1-2 pills a day (and I don't take them every day) and so far have not experienced any stomach upset.. which I often have issues with when taking a multi. They are more pricey than your normal drug store brands but I think they are better quality. They really give me the energy to push through my crazy, stressful, stand-on-my-feet-for-12-hours work days (without any jitters... just have more energy). Plan on buying again. The one downside is their size... they are huge gel caps...if you cannot do large pills... you may difficulty getting these down