Meditation can cause a lot of rest and peace. But can it also change the levels of hormone and neurotransmitters? Do they increase or decrease? I tend to think that fe your adrenaline is getting down and perhaps your testosteron. So can you become less 'male' or 'female' of it?
So far I have only one first-hand report of a practitioner diagnosed with ADD due to dopamine re-uptake problems, who says meditation helps him regulate the levels of dopamine.
From buddhist theory we know that the Four Jhanas meditation is intended to produce joy, which should correlate with the functioning of the reward mechanism of the brain, which is primarily dopamine-based. So another way to see the Jhanas, esp. the first and second one, is as mastery over one's dopamine levels by taking control of the reward mechanism.
As far the levels of other hormones and neurotransmitters, I can only assume they get "better", but there is nothing I know first-hand. A nice book on the topic seems to be Zen and the Brain: Toward an Understanding of Meditation and Consciousness but I have not read it.
from my personal experience, joy from meditation has exact feeling as when I take opiate but without crash landing or feeling down after. And given history of stokes in my family, I try to get brain MRI regularly every 5 years. I have a friend who is a neuro-radiologist to help me read my film. (I did my best to meditate while i was in that loud banging tunnel of MRI scanner). I think it had effect on my brain that control breathing....i forgot the name of it. it showed slightly brighter than normal.. not much but just a notch. he said typically that part of the brain would show brighter when activity is slow such as someone who is rescued from drowning or someone is taken very small amount of cyanide or when brain activities are slowing down (no need for large amount of O2 in that moment). I do not know if it has anything to do with my meditation but there it was. But, the over all finding was "normal".