Golden Brain's side-effect profile is worth reading in two parts, since only two of its four components are named.
Bacopa can cause mild stomach upset, nausea or loose stools, usually eased by taking it with breakfast; Lion's Mane is a mushroom, so anyone with a mushroom allergy should avoid it.
Because the rest of the formula is not disclosed, this site states directly it cannot rule out other effects or interactions — worth reading that honest limit before assuming the side-effect profile is complete.