Long term cocaine use and personality change - Scientific references? I've experienced cocaine addicts first hand and noticed the development of egoistic personality traits such as selfishness or loss of empathy in cocaine addicts. Are there any scientific references which support that observation?
I couldn't find a longitudinal study on this, which would be direct evidence, but it seems plausible due to circumstantial evidence:

Just taking a dose to lowers the perception of facial sadness (expressed by others)


Twenty-four healthy recreational cocaine users participated in this placebo-controlled within-subject study. [...] Findings show that cocaine impaired recognition of negative emotions; this was mediated by the intensity of the presented emotions. When high intensity expressions of Anger and Disgust were shown, performance under influence of cocaine 'normalized' to placebo-like levels while it made identification of Sadness more difficult. The normalization of performance was most notable for participants with the largest cortisol responses in the cocaine condition compared to placebo. It was demonstrated that cocaine impairs recognition of negative emotions, depending on the intensity of emotion expression and cortisol response.


In a cross-sectional study users/addicts did perform worse than controls on game-theoretical selfishness


The performance of healthy controls (n = 68), recreational cocaine users (n = 68) and dependent cocaine users (n = 30) in [...] social interaction paradigms (Distribution Game, Dictator Game) was assessed. [...] Decisions in the social interaction tasks of both cocaine user groups were more self-serving compared with controls as cocaine users preferred higher monetary payoffs for themselves.


In cocaine users


younger age-of-onset of cocaine use was associated with more pronounced empathy impairment [...]

Mean explicit and implicit emotional empathy ratings of the multifaceted empathy test (MET)
in cocaine users with an age of onset (AoO) of cocaine use ≤18 (n=27) and &gt;18 (n=73), and controls
(n=68). Cocaine users with an AoO≤18 showed less explicit and implicit emotional empathy than
controls and less implicit empathy than cocaine user with an AoO &gt;18. Error bars refer to SEM.
*indicates significant difference between groups (p&lt;.05)

With risk of being pedantic, this last study is also not direct evidence, because there could be some other factor (genetic or environmental) that causes someone to both take up cocaine use early in life and also cause them to exhibit lower empathy later in life (which is the only time when empathy was measured in this study design).