What are they?

L-Phenylalanine is an essential amino acid that can inhibit appetite by causing a release of cholecystokinin (CCK), which has been associated with an increase in satiety resulting in lower calorie intake. L-Phenylalanine also increases production of the neurotransmitter norepinephrine (NE). Increased levels of NE can enhance fat loss by activating hormone-sensitive lipase, causing rapid breakdown of triglycerides and mobilizing. 

Unlike appetite suppressant drugs utilizing controlled stimulants to reduce appetites, L-Phenylalanine has no undesirable side effects.