All therapy, practiced with any consistency, is effective -- probably because sacrificing for one's self builds up self-investment, and self-investment leads to self-protective decision-making that improves outcome and outlook.
Nootropics with perceptible feedback will always seem to be working. This might make their practice more consistent initially, but actually undercuts the build-up of self-regard by replacing it with dependency.
The statistical and analytical perspective is the mature way to handle objective decisions over stochastic processes, and it's the right approach for validating drugs at population scale.
But for personal assessments, decisions, and planning, the statistical can at best provide warnings about addiction or ineffectiveness. But more dangerously, it can give a veneer of objective confidence reinforcing self-destructive feedback loops, and suppress the uncertainty that would drive reflection and personal integration.
It's much better to embrace uncertainty, and share with a friend.