I normally take the recommended dose of Lion’s Mane but have taken 3 or 4 times that dose with no adverse effects. Been taking it most of the time for 4 or 5 years and when I run out I can really tell! (Because my ability to recall vocabulary really deteriorates).
That sounds a little like my short experience with Niacin.
The big minus to Niacin was that I had vivid and disturbing dreams, bordering on Awake Dreaming.
I took it hoping to boost brain function.
I later settled for using Vitamin B3 instead.