An alkaloid that works as a neurotransmitter in the brain, Phenylethylamine is claimed to help increase the levels of dopamine. The increase in dopamine is meant to make you “feel better.” Those suffering from depression, social anxiety, and the like often have low levels of dopamine in their system.
One study ((http://cat.inist.fr/?aModele=afficheN&cpsidt=2350263)) showed that when lab rats were directly injected with phenylethylamine their dopamine levels were, in fact, increased. The caveat, however, is that it was injected into them, not ingested. Most credible sources believe that phenylethylamine is metabolized so quickly that it is unlikely that it ever has a chance to reach the brain. So the research backing up phenylethylamine’s effectiveness when used in a diet pill is not only lacking, but is nonexistant.
The idea behind a diet pill including phenylethylamine is that it helps improve your mood and makes you feel better. I guess it’s possible for these positive feelings to help you want to eat correctly and exercise more, but I wouldn’t exactly call it causing you to lose weight. At best the link is very weak.
Phenylethylamine’s claims to aid in weight loss are to date still up in the air. For one, the act of it even getting to your brain has yet to be decided. And two, if it did, it’s doubtful that it would make a huge difference in your weight loss anyway. At this point, we’re looking for more research. But for now, don’t count on phenylethylamine doing too much for you.