The stimulant effect of caffeine becomes progressively less effective as you continue to use it regularly and build up a tolerance - if you were to intermittently drink strong coffee you would probably find it having a stronger effect on your ADHD. That said, from my experience the ‘rush’ you get from drinking caffeine only once in a blue moon is quite unpleasant and the positive effects aren’t really worth it… Caffeine imo is best consumed regularly or not at all.