There are a couple of concerns here, so let's look at them one at a time.
Yes, diagnosing someone with schizoaffective disorder, suspected or not, tends to be a difficult call, clinically speaking. The disorder itself is a mental illness characterized by recurring episodes of mood disorder and psychosis. Most doctors, if they suspect this disorder, prescribe a mood stabilizer and/or antipsychotic immediately. If the symptoms improve, the diagnosis is maintained and treatment continued. If not, the medications are either altered or removed.
Your main question, what would happen in the brain if the person did not have this issue is fairly easy to answer. The medications work by by blocking the receptors in the brain that certain neurotransmitters in the brain receive and process, such as dopamine. This action prevents excessive activity in the brain and helps to control symptoms. This drug regime is often prescribed to elderly patients as well, as those suffering with dementia related agitation are helped by this combination. In a younger adult without schizoaffective disorder, fatigue, tiredness, low motivation and a blunting of affect sometimes occur. (Blunting means that the normal range of mood expression is restricted.)
The most serious risk of this medication tends to be Neuroleptic Malignant Syndrome (NMS). This is a rare potential side effect of this drug and involves symptoms such as high fever; stiff muscles; shaking; confusion; sweating; heart rate or muscle pain and weakness. But this is very rare and generally does not occur.
Overall, the side effect that you will see in a person without schizoaffective disorder is sedation. They tend to sleep a lot more than usual. Permanent damage when taken short term is rare.
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