To provide another data point, my experiences with ceasing the use of lisdexamfetamine are pretty much in line with heavy long-term caffeine use: if you quit it cold turkey (or miss a day or two due to the quirks of the doctor/Rx system for this stuff (if you take it plan ahead and make sure your new prescriptions don’t have to be issued on a holiday)) expect a week or more of fog and brain-splitting headaches and lethargy. It’s better to stop slowly. Cutting your dosage by 25% each day and then holding at a minimal dosage for a couple days seems to work the best for some.
Also if you have issues with addiction, it’s probably best to stay away entirely. The mental quieting it’s prescribed for is inferior to that of a good cup of coffee (entirely subjective, YMMV) and there are a whole host of negative physiological and psychological side effects.
2¢ of unsolicited advice: if you need this stuff to keep your brain on track so you can handle your job (especially post-2020), and your doctor suggests it, might be worth considering after exhausting other options — at least that was the case for me, it can be worth it. But if you’re surviving otherwise and just want a focus boost the risk:reward ratio is way off.