However, the digestive system brakes down phenylethylamine. Studies in people found that eating up to two pounds of chocolate a day causes no increase of PEA in urine or the blood stream. People in the initial stages of attraction have increases in both. The fanciful effect noted by chocolate-lovers is a simple result of extremely large amounts of caffeine and sugar. Recent studies on monogamy in mammals have focussed on the endorphins, vasopressin and oxytocin.
Endorphins are neuromodulators in that they can effect the rate at which nerves fire.
Oxytocin serves several functions in the body including control over uterine contractions, cervical softening, and penile erection in the male. Other oxytocin-receptive nerves act in the modulation of pain as well. Vasopressin typically is known for action in the cerebral cortex aiding in memory. These endorphin studies have centered on the vole, a tiny mouse-like rodent that lives in the Midwest United States. Two species of voles, although similar in most respects, differ greatly in terms of mating habits.