Long arginine 3-IGF-1 , abbreviated as IGF-1 LR3 or LR3-IGF-1 , is a synthetic protein and lengthened analogue of human insulin-like growth factor 1 (IGF-1). [1] [2] It differs from native IGF-1 in that it possesses an arginine instead of a glutamic acid at the third position in its amino acid sequence ("arginine 3"), and also has an additional 13 amino acids at its N-terminus (MFPAMPLLSLFVN) ("long"), for a total of 83 amino acids (relative to the 70 of IGF-1). [2] The consequences of these modifications are that IGF-1 LR3 retains the pharmacological activity of IGF-1 as an agonist of the IGF-1 receptor , has very low affinity for the insulin-like growth factor-binding proteins (IGFBPs), and has improved metabolic stability . [1] [2] As a result, it is approximately three times more potent than IGF-1, [3] and possesses a significantly longer half-life of about 20–30 hours (relative to IGF-1's half-life of about 12–15