There is no established “normal” level of any given neurotransmitter.
Different people will have different innate tendencies towards euphoria, melancholy, mania, depression, psychosis, dissociation, etc., and this varies throughout an individual’s lifetime as well. This variability does not necessarily correlate to comparatively lower levels of neurotransmitters like serotonin, norepinephrine, GABA, and dopamine.
Our brain biochemistry is responsive to socioecological stimuli and shifts in our habitat/environment, e.g., depressing conditions increase rates of depression among vulnerable individuals, and can even induce depression in people who might otherwise not be prone to it. This is true for other states of so-called mental disorder as well.
Given all of the above, to say mental illness is caused by a chemical imbalance is incorrect, and in fact harmful.
Why is it harmful?
The medical model is a tool of individualism and neoliberal capitalism. By compartmentalizing mental disorder into individual differences and vulnerabilities, we:
– elide the systems and structures that create the conditions which allow mental suffering to persist,
– enable preferential treatment of pharmaceutical interventions that can cause serious and permanent physical harm, and
– provide justification for the forced treatment, incarceration, and torture of psychiatric inpatients, as well as coercive mental health conservatorships.
Your mental distress not being caused by a chemical imbalance does not make your suffering less real or less worthy of treatment to alleviate it. It does not mean that you are responsible for your condition or that you are not disabled by your condition.
To explode the binary of sane/insane we must recognize mental health as a spectrum, like the spectrum of bodies, of neurotypes, of health in general. We are not imbalanced. We are beautifully diverse humans navigating an unbalancing time.