If a person's brain has a low level of neurotransmitters how would this affect the person

This depends on the neurotransmitter deficiency. neurotransmitters are often decreased or imbalanced in the setting of mental health or psychiatric disorders as well as various neurologic disorders. for instance, the deficiency of the neurotransmitter dopamine is one of the main etiologic causes of parkinson's disease; the deficiency of the most abundant neurotransmitter acetylcholine will lead to body weakness similar to myasthenia gravis or lambert-eaton syndrome. in conclusion, the affectation of low levels of neurotransmitters depends on the neurotransmitter involved.