Chemistry and biology of the mind/brain?

Want to read popular science books (preferably by actual PhDs) on the chemistry and biology of the mind/brain.

I'm really interested in the brain as a physical object and the chemical/biological processes within it. Especially in relation to mental illness — for example, depression and schizophrenia.

I'm just really fascinated by the fact that taking, I don't know, say, lithium can alter one's behaviour and mental state! Like how does that happen? (I know the mechanism of lithium — and other meds — is not fully known, but would be interesting to read in depth the theories!)

(I'm not looking for books about "consciousness" and philosophy of consciousness – I've read those already. More interested in the chemistry/biology aspect.)

I'm an academic myself so prefer in-depth/dense ones (that are not boring!) than light, surface-level ones.

Thank you!