In chemistry, neurochemistry is the study of the chemical function and operation of the nervous system. [1] In detail, this includes the study of cellular neurochemistry and neural membranes; intercellular signaling; intracellular signaling; growth, development, and differentiations; metabolism; inherited and neurodegenerative diseases; sensory transduction; and neural processing and behavior. [2]

Human chemistry
In human chemistry, research efforts over the last few decades has focused on how various neurochemicals, in particular oxytocin, vasopressin, endorphin, dopamine, serotonin, norepinephrine, testosterone, estrogen, epinephrine, phenylethylamine (PEA), dehydroepiandrosterone (DHEA), brain-derived neurotropic factor (BDNF), monoamine oxidase (MAO), gamma-aminobutyric acid (GABA), prolactin, cortisol, progesterone, estradiol, nerve growth factor (NGF), gonadotropin-releasing hormone (GNRH), among others, related to various moods, e.g. happiness, and states of human existence, e.g. being in love, in relation to changes in human bonding. [3]

References
1. Neurochemistry (definition) – Dictionary.com.
2. Siegel, George J.; Albers, R.W., Brady, S.T., Price, D.L. (2006). Basic Neurochemistry, 7th Ed.. Academic Press.
3. Thims, Libb. (2007). Human Chemistry (Volume Two), (ch. 12: “Bond History and Neurochemistry”, section: Neurochemistry, pgs. 503-13), (preview), (Google books). Morrisville, NC: LuLu.