IGtropin IGF-1 Long R3 Long R3 IGF-1 ACTIVE INGREDIENT Long R3 IGF-1 is an 83 amino acid analog of IGF-1 comprising the complete human IGF-1 sequence with the substation of an Arg(R) for the Glu(E) at position three, hence R3 ,and a 13 amino acid extension peptide at the N terminus. This analog of IGF-1 has been produced with the purpose of increasing the biological activity of the IGF peptide. Long R3 IGF-1 is significantly more potent than IGF-1.