Things work different for different people, you can’t get a universal answer to this question.
Your brother should pay attention to is he experiences any side effects, and hopefully he has a good doctor that pays attention if he has any questions.
The principle of GLP 1 is quite elegant IMO, but that’s the case for most medicine that works. Doesn’t mean there can’t be minor or even serious side effect.

There is a danger of malnutrition if you overdo it, and malnutrition can lead to all sorts of conditions. But I really really hope he is being well informed by his doctor.

Best of luck to your brother. 👍