Is chemical imbalance real or a myth?

Thoughts on chemical imbalance?

I (31F) was diagnosed unspecified bipolar disorder with mixed features and ADHD. My last episode ended up with me hospitalizing myself.

Does anyone else ever doubt the chemical imbalance theory? Like, how is it that people with bipolar “have a chemical imbalance” and other humans don’t?

I have a friend who has a masters in neuroscience and keeps trying to convince me that we don’t really know what bipolar, ADHD and all other mental health issues are. We don’t know what defines it, but it’s moreso solely because of our thoughts and life scenario. That the idea of a chemical imbalance is made up.

She said she was diagnosed bipolar, her therapist told her she was not bipolar and she quit her meds cold turkey. Says my bipolar is fake and being medicated is not helping me, will never help me and I have to do deep work. Which I’ve been doing for years. I’ve heard this from a lot of people as well. And that my ADHD can be corrected with strict behavior on my end.

This actually infuriates me because since being diagnosed (which took a long time), I can look back and identify all my symptoms. And being put on actual bipolar meds has worked wonders. No wonder why SSRIs and SNRIs never worked for me.

What are your thoughts?