IGF-1 DES is a naturally occurring variant of insulin-like growth factor 1 missing the first three amino acids, a change that sharply reduces its binding to carrier proteins and makes it more potent but short-acting. The theory behind its use is that this brevity confines its effect to nearby tissue rather than the whole body. Whether that holds in practice has never been tested in a human trial. Like its relative LR3, it was developed as a research reagent rather than a medicine, it is not the approved recombinant IGF-1 used for a rare growth disorder, and it carries the same theoretical concerns that attach to raising growth factor signalling. It is prohibited in tested sport.