I watched the chemical imbalance theory absolutely gut the person who used to be my mother. Over a period of maybe 10 years and multiple medications I watched her gain weight, get grey hair far too early for her age, she had periods where she either couldn't stay awake past 9:00pm, or couldn't sleep at all, periods of near catatonia, periods where rest was impossible.
She was a guinea pig for decades and it became abundantly clear toward the end that none of these doctors had a god damn idea what they were doing.
Even given my experience, I wouldn't rush to vilify them as criminals. I take an SSRI daily myself and it _helps_, and I owe gratitude to the science that has been done to get this far.
The problem is that all of these doctors are operating _without data_. They'll tell you that your seratonin levels are too low, or this or that, but if you ask them how low... they can't answer. If you ask them why they're low, they can give you common answers, but none that are unique to your physiology.
So you have schizophrenia? Let's try bloodletting, leaches, and an assortment of drugs that will affect the balance of chemicals in your brain in unknown ways. Don't worry about the side effects, here's a cookie to help with the blood loss.
She was a guinea pig for decades and it became abundantly clear toward the end that none of these doctors had a god damn idea what they were doing.