Chronic cocaine usage prevents the body’s formation of fat storage and causes long term difficulty in maintaining a healthy weight. The appetite suppressant only adds to this problem, and it last much much longer then 15 minutes. The cocaine anhedonia also commonly leads to people eating less food, rather then more, as the body is not motivated enough with dopamine to consume.

Cocaine also increases metabolism by a significant margin, along with increasing body temperature. Both leading to an increased burning of calories even when stationary and at rest.

So while it is possible, gaining weight on cocaine is really damn hard. It is mostly a symptom of getting clean off of cocaine.

Meth is a whole other league though, and I will agree.