GlaxoSmithKline invested milions of dollars into research of cardarine aka gw501516 and then abandoned it in phase 2 because it showed that the drug caused cancer to develop rapidly in several organs, at dosages of 3 mg/kg in mice and rats.
In 2013, WADA took the rare step of warning potential users of the compound of the possible health risks, stating that "clinical approval has not, and will not be given for this substance"; the New Scientist attributed the warning to the risks of the drug causing cancer. ( source: wiki ).
Now really comparing protein and drugs is like apple and oranges.
We dont know how dangerous it is, but if a company abandons the research after investing milions then u really dont need to know more.