You sound like your company would be really good for him and you're a good sibling for looking for any options to steer him clear of this. Whatever happens you definitely tried.
There are things the US military does a good job of advertising itself as that go beyond a job market. Brotherhood, camaraderie, and giving your life meaning are all things the US military spends millions if not billions making young people think it can provide.
You should know that so far basically nobody knows how to reliably lose weight and keep it off at a population level.
At a population level? Affordable healthy food, promoting an active lifestyle, and reduced stress...this stuff isn't a mystery. Weight gain in the average person isn't due to 'overeating' (ED or otherwise) it is due to sedentary lifestyle and the easy accessibility of nutrient poor, calorie dense, cheap food.
I had a colleague tell me that GLP-1s inhibit individual fat cell (adipocyte) growth, but can ultimately lead to adipocyte proliferation, especially if lifestyle modifications aren't made, and that this is a major factor in rebound weight gain. Can't speak to the veracity myself and am having trouble interpreting the literature off-hand.
Nausea and diarrhea are the most common side effects. GLP-1s are a part of a broader class of medications called incretin mimetics, which basically trick your body into thinking it has eaten recently. The nausea and diarrhea are due to this but there’s actually no food to digest.
They are amazing drugs to lose weight and improve overall health, but can be incredibly expensive even with insurance. You may need to wait up to a week after receiving the prescription for a prior authorization from your insurance. Get a manufacturer coupon if you have private insurance or ask your pharmacy to get one for you.
If you do start one, be sure you start at the very lowest dose and stay at that dose for at least a month. If you don’t start low the side effects can be crippling.