I tried Niacinamide (500mg 2x/day) months ago and noticed absolutely no improvement in my memory.
I even tried the 1,500mg timed-release 2x per day as someone else posted, with no improvement either.
After reading the claims, I was so optimistic. :(
I've also tried Lion's Mane and Taurine, both separately and together and experienced some (slight) improvement, but not enough to continue taking them, since they were expensive.
According to Mary Post's article on EC, the best way to take niacinamide for Alzheimer's is... "250 mg. every 90 minutes, 12 times a day seems to be the best method." However, I would research liver toxicity and niacinamide first before taking this large amount if I were you.
A great supplement I take for memory is Citicholine. I started having impressive memory recall the day after I started taking it!