There is certainly a potential to build a tolerance to stimulants, and that's one possible reason to switch drugs. As you said, it varies from person to person.

There is certainly a potential to build a tolerance to stimulants, and that's one possible reason to switch drugs. As you said, it varies from person to person. For drugs with minimal withdrawal symptoms, like ritalin, it is also possible to mitigate tolerance effects by taking regular vacations from the medication. Out of curiosity, have you had to increase your dosage significantly as an adult? It is common for people to need to increase their dosage during adolescence because their bodies change, and that's not necessarily indicative of a tolerance effect.