Erythropoietin (EPO): A 165 amino acid glycoprotein hormone (glycoproteins consist of several sugar molecules linked with a protein molecule). EPO stimulates erythrocyte (red blood cell) production in the bone marrow, boosting the blood's ability to carry oxygen. Studies have shown that significant amounts of EPO resist digestion and survive to reach receptors in the intestinal tract. One raw milk-drinking athlete was wrongly accused of blood-doping, so there's at least anecdotal evidence of EPO's activity in our systems!
Several studies have shown acute peripheral administration of PYY 3-36 inhibits feeding of rodents and primates. Other studies on Y2R- knockout mice have shown no anorectic effect on them. These findings indicate PYY 3-36 has an anorectic (losing appetite) effect, which is suggested to be mediated by Y2R. PYY-knockout female mice increase in body weight and fat mass. PYY-knockout mice, on the other hand, are resistant to obesity , but have higher fat mass and lower glucose tolerance when fed a high-fat diet, compared to control mice. Thus, PYY also plays a very important role in energy homeostasis by balancing food intake.  PYY oral spray was found to promote fullness.  Viral gene therapy of the salivary glands resulted in long-term intake reduction. 
The term peptide has been used to mean secretagogue peptides and peptide hormones in sports doping matters: secretagogue peptides are classified as Schedule 2 (S2) prohibited substances on the World Anti-Doping Agency (WADA) Prohibited List, and are therefore prohibited for use by professional athletes both in and out of competition. Such secretagogue peptides have been on the WADA prohibited substances list since at least 2008. The Australian Crime Commission cited the alleged misuse of secretagogue peptides in Australian sport including growth hormone releasing peptides CJC-1295 , GHRP-6 , and GHSR (gene) hexarelin. There is ongoing controversy on the legality of using secretagogue peptides in sports.