The chemical imbalance idea is an oversimplification of what is going on. There is evidence that giving a serotonin agonist helps symptoms of depression, giving a dopamine agonist helps ADHD symptoms, a dopamine antagonist helps with some symptoms of schizophrenia, etc. Therefore, you want to conclude that if blocking (or increasing) a neurotransmitter relieves symptoms, that the person did not have the right levels of the neurotransmitter in the first place, thus, a chemical imbalance. The problem with this idea is that simply changing the levels of a neurotransmitter does not necessarily cause a clinical effect. Take depression, once you start taking an SSRI, your serotonin levels start to increase right away, but you will not see the mood enhancing effects for a couple of weeks. This is likely because there are issues with serotonin receptors, and the flood of extra serotonin helps to reset them. For schizophrenia, if too much dopamine was the answer, we would expect to see increases in its metabolites, but we do not. More likely, there is a problem in the pathway that projects dopamine from the midbrain to the forebrain, which causes it to not function properly as negative feedback, therefore allowing over-activity of dopamine pathways from the midbrain to the limbic areas.

I personally believe this is why many invidivuals report post-trip lessening of depression or anxiety, cessation of smoking or other addictive behaviors such as gambling, and even improvement of cluster personality disorders symptoms in some cases. It's not an inherent neurological trait, but a complex interaction in the way that you view the self and society. Psychedelics allow people to view situations and experiences in a way they've never viewed them before, and in a way this is giving a key to a perspective that they've never heard before but resonates deeply with them, helping to initiate serious change.

Like you wake up feeling great and ready for the day, prepare your breakfast while thinking about all the cool things you want to do during the day, then you sit down and start crying for no reasons, and you’re now in the worst mood ever with very little control over how you feel. The whole thing is really violent.

> If left untreated, depending on severity, this can lead to suicide, delusional thinking, schizoid breaks, homelessness and very often self treatment with illicit drug use.

I am current in most of these states; homeless, suicidal, and just suffered psychosis during a covid infection and dealing with an odd perception of reality. Talking to people about their sadness I know, luckily, most people do not know what depression is. There is such large gap between mental health and mental illness.

That isn’t necessarily a bad thing, but it’s probably not worth criticizing a study that is looking in a different subset domain of interest.