Amphetamine(which is what benzedrine was) is pretty overrated as a weight loss drug in the general population. It causes a short window of reduced appetite and probably increased catabolism(due to increased heart rate) which peters out after a couple weeks on the same dose. That leads to a short period of rapid weight loss that pretty much grinds to a complete halt, after which regaining the lost weight is quite typical.

On the other hand, if like me, you have ADHD and weight issues, it could be more helpful. Because it could treat your ADHD enough to help you actually establish and follow a structured diet and exercise regime. Especially if your ADHD includes impulsivity. The last time I was on lisdex treatment, I lost about 5kg from the initial boost, a lot of it was probably water weight. Then I managed to cut about 30kg later with calorie counting and regular cardio.

So the physical effects themselves are largely a pisstake.