Psychobiology has studied social bonding and attachment from a CNS perspective. However, what is going on in the brains of human beings when they feel the subjective feeling of "love" or "being in love"? Zeki, 2007 (the year of many reviews on this topic) wrote a most wonderful paper "the neurobiology of love" in which he points out that it's all about positive and negative emotions and that we are addicted towards positive emotions. Interestingly, love and hate appear to share at least some major brain areas (Zeki and Romaya, 2008), maybe not unexpectadly, as most reasons of hate are somehow related to non-responded love. One molecule that seems to be involved in "romantic love" is the neurotransmitter oxytocin, a peptide hormone (see structure below), which apparently is indirectly involved in love perception.
This molecule increases trust and reduces fear. In a risky investment game, experimental subjects given nasally administered oxytocin displayed "the highest level of trust" twice as often as the control group. It also works by affecting generosity by increasing empathy during perspective taking. In an experiment, intranasal oxytocin increased generosity in the Ultimatum Game by 80% but has no effect in the Dictator Game that measures altruism. Perspective-taking is not required in the Dictator Game, but the researchers in this experiment explicitly induced perspective-taking in the Ultimatum Game by not identifying to participants which role they would be in. As Starka, 2007, pointed out: "Throughout literature--fiction and poetry, fine arts and music--falling in love and enjoying romantic love plays a central role. While several psychosocial conceptions of pair attachment consider the participation of hormones, human endocrinology has dealt with this theme only marginally. According to some authors in addictology, falling in love shows some signs of hormonal response to stressors with changes in dopamine and serotonin signalling and neurotrophin (transforming growth factor b) concentration. Endorphins, oxytocin and vasopressin may play a role during the later phases of love. However, proof of hormonal events associated with love in humans has, until recently, been lacking." I believe that in order to achieve this, we should have a more complete analytics, which considers all peptides and secondary metabolites, including lipids. If we could do biochemistry of thr brains of people in love vs. normal vs. people who hate then we should be able to detect molecular patterns of substances produced differentially. But this is a long way to go. In the meantime, sellers of modern "love potions" like marketed oxytocin (e.g. as Pitocin) or people who put GHB, a GABA B ligand (see structure below)
into the drinks of others (without them knowing), to increase their oxytocin levels and make them feel open and good (and induce sleep, see Rifat on GHB) will at least subjectively increase love, if at all, - but maybe the answer is not in the chemistry but in the philosophy.