Phenylethylamine is found in animals in the same capacity as it occurs in humans: as a neurotransmitter, responsible for feelings of contentment and bliss (as I discuss here).

Phenylethylamine hallucinogens also occur in the natural world, although only in a very small population. It occurs in approximately twenty species of cactus, and has not been found anywhere else capable of inducing hallucinations.

Within the human body, phenylethylamine is fairly common, found throughout the body in various tissues, the bloodstream, and the brain. Some of its derivatives include (R)-1-(4-Methylphenyl)ethylamine, (S)-1-(4-Methylphenyl)ethylamine, (R)-1-(4-Bromophenyl)ethylamine, and (S)-1-(4-Bromophehnyl)ethylamine. Although I probably don't understand those names any more than anyone else, they are more neurotransmitters. The immediate precursor of phenylethylamine is L-phenylalanine, and the synthesis also requires decarboxylase.u