How long do the effects of fat-dissolving injections last?

Even with exercise, the stubborn fat on my arms just won't go away, so I'm considering getting fat-dissolving injections.

How long do the effects of fat-dissolving injections last? I am curious about when the effects usually first appear after the injection and how long they last.

I am curious if the reason the effects or duration vary from person to person is also influenced by exercise and diet management.
I'm wondering if the fat might increase again once the effects wear off.