I got this from Reddit (I know, sorry)

"u/reinschlau • 1y ago It's a joke. But out of curiosity I ctrl+f'ed through the collected works, and the only mention of cocaine was in a letter from Engels to Ludwig Kugelmann (volume 48), in 1889 (after Marx's death, when Engels would have been editing Capital vol 3 and whatever else Marx left behind):

Dear Kugelmann, A Happy New Year to you. Thank you for the prescription for my eyes, which, however, is not nearly concentrated enough for me. Last year and up till August I used cocaine and, as this grew less effective (on account of habituation), went on to ZnCl 2 , which works very well.

But there are also relevant discussions of alcohol and opium in The Condition of the Working-Class in England and elsewhere."

It seems to cover most of it. You probably have to read the relevant parts on alcohol and opium to get the full picture but it is mostly a joke.

PS the uses of cocaine as a medication in olden days is pretty fun some times. I once saw an ad for cocaine as a "nasal anesthetic". I bet that flew off the shelves. Seriously though, it was probably fairly expensive and diluted.