no appetite and nausea

My boyfriend has a problem with eating and I have no idea how to help him or get a diagnosis.  The majority of the time, he has little to no appetite.  When he tries to eat, he ends up eating very little or nothing due to the nausea he feels.  He claims that the only way he gets an appetite is to smoke marijuana.  If he lifts weights, he also claims that he doesn't need to smoke the marijuana and his appetite increases.  He is approximately 5'10" and his weight fluctuates between 130-140 pounds.  

[Renee Radenberg]

He is appropriately 20-25lbs underweight for his height. From your statement, he is not eating too well, not exercising, has nausea, and needs a drug (marijuana) to gain an appetite. Suggest you have him see an MD for help with his issues you have stated above.