Can you give us some more information about the type of odor? When does it occur?
Is it breath/sweat/skin?
What is the age and general health of the patient?
Do they take any medication?
Do they ever drink alcohol?
The first thing is to rule out a physiological cause of the odor which may possibly be ketones on the breath through either a medical condition such as diabetes or a diet that is too low in carbohydrate (the Atkins diet was a common cause of ketone production).
With taking zoloft then we recommend avoiding alcohol owing to the risk of interaction and the alcohol also will cause problems when taken with some blood pressure medication. Because they take diet pills and alcohol then I would also suggest a liver function test however if they are actively dieting then the most likely cause is the ketone issue.
This can cause a problem with kidney function if ketone levels get too high so kidney function tests are also recommended.
I would recommend a health check with their doctor in order to rule out some potentially serious problems.