Some of the approved drugs are synthetic versions of the natural hormones, such as trenbolone acetate and zeranol. Just like the natural hormone implants, before FDA approved these drugs, FDA required information and/or toxicological testing in laboratory animals to determine safe levels in the animal products that we eat (edible tissues). Furthermore, FDA required that the manufacturers demonstrate that the amount of hormone left in each edible tissue after treatment is below the appropriate safe level. As described above, a safe level is a level which would be expected to have no harmful effect in humans.
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!