efficacy of alleged nootropic substances in most cases has not been conclusively determined. This is complicated by the difficulty of defining and quantifying cognition and intelligence . Contents [ hide ] 1 Availability 2 Therapy or enhancement 3 Examples 3.1 Replenishing and increasing neurotransmitters 3.1.1 Cholinergics 3.1.1.1 Piracetam 3.1.1.2 Aniracetam 3.1.1.3