I apologize if my response is kind of all over the place. I am somewhat of rush this morning, but I wanted to throw my hat into the ring.
To contrast the other user who replied, I have been on stimulants for 8 years now.
I will say that there is a very notable drop in efficacy. Not enough to justify stopping them all together, but I'd say I get about 50% of the benefit on my best days.
I would consider my current experiences much like that of caffeine. It worked amazingly in the beginning, but now I feel like they are necessary to achieve a baseline sense of normalcy. I could raise the dosage, I suppose, but I do not want to go down that path again because it is just a temporary fix.
Honestly, taking time off stimulants has been more effective than increasing dosages. Most people can stop stimulants with little to no issues, but since I have adapted to them over the years, the withdrawals are pretty fucking uncomfortable and debilitating. Though, according to my medical professional of questionable quality, my experiences are still unusual. Still, I try to take weekends off, and it's been helpful none the less.
Going forward, I am thinking of switching to a non-stimulant, which may be an option for you as well if you are indeed ADHD. Despite how ever effective stimulants may be, I believe I am starting to lose more from them than I am gaining from them. At least where I live, the constant drug-testing and various laws surrounding controlled-substances makes stimulants almost not worth it.
The medications can be life-changing, but in the ADHD community, it's well known that there is a honeymoon phase (it's not uncommon to experience stimulant-induced euphoria), thus the real judge of how effective they are should be determined once that period is over. However, not everyone gets that honeymoon period, but I sure did for a few weeks.
If I must be entirely honest, I think that the medications do help, but I never have thought they helped enough. They make life easier, but not easy, and that is something I think I have really struggled to come to terms with. I went in with expectations of a silver-bullet, but left with a tool. My fair warning would be to be careful what you read about ADHD medications online.
One other point that I feel I should warn others about -- something no one ever told me -- is to not let meds give you enough rope to hang yourself. What I mean is: I built a career and a life while having access to these medications. Recently, there has been a nationwide shortage in my area. Every pharmacy was out of stock -- literally none in my area had anything. Zero. Nada. I was working on a big project at work, and basically had to put the entire thing on hold for three weeks because once I ran out -- I was flat useless. I couldn't believe how much I depended on them to do my work. It caused me a lot of stress and anxiety realizing that I am basically living a variant of the plot of "Flowers for Algernon" and that without these medications, I seriously do not think I could maintain the life I was able to build on them. I am not trying to scare you away, but I feel like it would be dishonest to not include both the good and the bad.
If you have anymore questions, I'd be more than glad to try to answer them.