EPO

A glycoprotein hormone acting at the EPO receptor on red-cell precursors in bone marrow, raising red cell production and therefore oxygen-carrying capacity. The effect builds over weeks, because red cells take weeks to make.

An approved medicine with strong evidence in its actual indication — anaemia from kidney disease and chemotherapy — where it is dosed against blood counts by someone monitoring them. We publish no performance ladder for it, and this is the only compound on the site where we make that call. The reason is specific rather than squeamish: the effect people want is a raised red cell count, and a raised red cell count thickens blood. Without haematocrit monitoring the margin between the effect and a clot is invisible from the inside, and the endurance-sport record of the 1990s is what that looks like at scale. If you are considering it, the thing that makes it survivable is bloodwork, not a number from a website.

Approved, effective, and one of the very few things here with a documented record of killing healthy young people when used without monitoring. Both facts belong in the same sentence.

EPO is discussed very differently from everything else in this catalogue, and the difference is instructive. There is no casual community around it. The endurance world's own account of the 1990s - riders dying in their sleep, a haematocrit ceiling introduced as a safety limit rather than a fairness one - is retold as a cautionary story, not as a protocol. The people who do discuss using it are overwhelmingly focused on monitoring: haematocrit, haemoglobin, iron status, blood pressure, and the fact that iron has to be adequate or nothing happens at all. That focus on measurement rather than on effect is the clearest signal the community sends about it.