system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are Adderall, Ritalin and other medications with side effects used to treat dopamine deficiencies rather than dopamine itself?

And by that I mean, why use medications that attempt to cause the production and modify the uptake of dopamine rather than using dopamine itself as a medication and directly supplementing a person's dopamine levels? I mean, sure, you'd have to ensure that the release of the dopamine is gradual rather than all at once, but it's not like that's nonexistent technology; patches and a bunch of other things exist to allow for that. And yes, I'm aware there's some talk about whether common dopamine deficiencies are the result of norepinephrine deficiencies instead of dopamine deficiencies, but that leaves me with a nigh-identical question.
gpt
Dopamine itself cannot cross the blood-brain barrier.  You can shoot someone full of dopamine via an IV all day long, but it will not do anything to affect the dopamine levels in the brain itself.  So, the best thing you can do is either stimulate the brain to produce more itself or limit its reuptake.