It means that they had too many drugs [ coke=cocaine]

Jura is correct. I would only add that the stereotype of cocaine addicts and crackheads, at least in regards to weight, is "very skinny." Sometimes to the point of unhealthy. An example would be the singer Amy Winehouse who was a full-figured woman just a few years ago and now is skinny to the point that a strong wind would knock her over. Hope that helps.