That's what side effects are. Anytime you take psychoactive medications, they're going to mess with a thousand different brain systems that ALSO happen to use the neurotransmitter(s) affected by the drug, but were functioning normally. Thankfully, the brain is usually pretty good at compensating for stuff like that (which is why drug tolerance is a thing). Otherwise, side effects would probably be a LOT worse in general.

But when you say you're worried about schizophrenia, that's still thinking about it wrong. Schizophrenia is not caused by a simple overabundance of dopamine, it's caused by some kind of complex disturbance in the activity of one or more networks of brain circuits. The fact that some of those circuits have some dopaminergic components, and that some of the drugs that can partially alleviate symptoms affect dopamine among other neurotransmitters does not make dopamine central to schizophrenia.