Effects - Peptide Hormones carry messages around the body to stimulate specific functions - eg to increase growth or to control pain. Athletes may use these substances to increase muscle size and strength or to improve the body´s ability to carry oxygen to the muscles. They could do this by taking erythropoietin (EPO). Dangers - prolonged use could cause muscle wasting; enlarged internal organs; increases risk of blood clotting. Analogues are synthetic drugs which have similar effects to peptide hormones. Both are banned in sport.