Apart from the risks that accompany drugs with dopaminergic effects, amphetamines, even when used to treat neurological disorders like ADHD, have been known to frequently and predictably cause anorexia, weight loss and insomnia. High doses can cause psychotic behavior, and even normal doses have been known to produce psychosis that ranged from the loss of short-term memory to horrific visual and auditory hallucinations. Are you getting the impression that using synthetic stimulants to flood your brain short-term with excessive or unnaturally high levels of hormones and neurotransmitters may not be a good idea, especially when done frequently or in excess?
Cognizin– this is a derivative of citicoline. It increases* the levels of acetylcholine neurotransmitters, dopamine, and noradrenaline in the brain. These are neurotransmitters essential for brain functioning. Besides this, Cognizin maintains the functioning and stamina of neuronal cell membranes and enhance* energy production from the frontal cortex. With this, you will have increased mental reaction time, expanded focusing ability, improved* immediate and short-term verbal memory and augment the brain’s metabolism.
In fact, this body-mind connection has become so relevant to our current era that communities like Mental Health America are devoting their efforts to create a challenge that raises awareness on how lifestyle plays an important role on our mental health. While our generation is definitely more conscious of our bodies and the importance of a healthy lifestyle, it's a good reminder that the body is like a machine and we should listen to it, tune it up, and update the system every so often. 
A fancier method of imputation would be multiple imputation using, for example, the R library mice (Multivariate Imputation by Chained Equations) (guide), which will try to impute all missing values in a way which mimicks the internal structure of the data and provide several possible datasets to give us an idea of what the underlying data might have looked like, so we can see how our estimates improve with no missingness & how much of the estimate is now due to the imputation:
The main concern with pharmaceutical drugs is adverse effects, which also apply to nootropics with undefined effects. Long-term safety evidence is typically unavailable for nootropics.[13] Racetams — piracetam and other compounds that are structurally related to piracetam — have few serious adverse effects and low toxicity, but there is little evidence that they enhance cognition in people having no cognitive impairments.[19]