Why does taking cocaine make you so skinny?

Appetite effects: Cocaine causes an increase in neurotransmitters, the same neurotransmitters that are increased by food. The same Dopamine one gets from eating a nourishing meal can be replicated by the administration of cocaine. The lack of adequate nutrition in the context of Cocaine use disorder can exacerbate the deterioration in health that unchecked substance abuse can wreak. Stay safe!

It impair food drive: Certain drugs including opioids and Cocaine have ability to impair food drive. Drug users are loosing weight because they just do not perceive hunger/need to eat. Needless to say though that outcome of such weight loosing strategy very dismal. It is addiction.