Example: Josh is so interested in mathematics that he sits for hours and hours working on the problems. He forgets to eat. He lost weight, he doesn't clean the house and doesn't even notice what's going on because all he wants to do is his work.
There is a slang expression
that doesn't include the negative side-effects of obsessive work with something that actually produces results but also has very negative side-effects.
Example: Henry likes computer programming so much that software development is all he wants to do. He has no social life and he speaks of advanced computer science with non-technicians so that he doesn't get understood. It takes a Ph D in computer science to understand what Henry is talking about and he is only 14 years old.