I mean, if you think about what a brain is, you could consider basically any any mental disorder is just a "chemical imbalance". Saying that depression is one i

I mean, if you think about what a brain is, you could consider basically any any mental disorder is just a "chemical imbalance". Saying that depression is one isn't false, but, to your point, I think pharmaceutical companies harp on this point in order to sell antidepressants. What GP gets right, though, is that depression != sadness. It is normal (and often healthy) to feel sadness after experiencing loss or other hardships. It is not healthy to feel hopeless and devoid of energy for months on end... that's what depression is.