I honestly think a good amount of people are reacting to very shitty surroundings and patterns of living. People are essentially just animals, and despite common opinion, we are still highly instinctual beings that have next to no ability to see the base cause--effect of things in our day to day lives.
If you have never noticed the pill pushers, you have never been that involved with the system, or are unwilling to see it.
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And yes, the term chemical imbalance is a crock of psuedo-science bullshit that invalidates and sweeps under the rug any real attempt at understanding what is happening.
"Durr hurrr it's just an imbalance"
I tend to see the people who use the phrase as no different from ancients sacrificing members of the tribe to their gods to keep them happy.
It's the thinking of people that surrender any and all control over themselves they might have because of what other people say or do.
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And no drugs "treat" mental illness---psychiatrists know this. These drugs essentially alter the brains functioning until the people observing the patient no longer see them as being problematic or at risk of injury to self or others.
It's basically sedating and numbing away a part of the brain to lower the volume of dysfunction, rather than healing the dysfunction. This has both short and long term health implications by itself.
With depression sometimes this is more like being pushed out of a rut, which is fine when the meds can be stopped, but the problem is the low success rate of meds, not knowing how they work, knowing little how they effect kids despite kids getting prescribed them, and the sheer volume of this crud being consumed.
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And in response to Cancerblack, a GP made me horribly sick giving me an antipsychotic without telling me what it was, then months later lawsuit commercials for said medication were blasting every 10 minutes.