IGF-1 or Insulin-like Growth Factor is a peptide that is capable of managing and regulating levels of growth hormone (GH). IGF-1 LR3 is a lengthened version of IGF-1. IGF-1 LR3 is a chemically altered amino acid chain made of 83 amino acids. At position 3 on the chain Glu(E) was substituted with Arg(R), which gives the name LR3. By making this substitution at position three, IGF-1 is inhibited from binding to certain proteins in the body, thus increasing the half-life (https://www.prnewswire.com/news-releases/igf-1-and-long-igf-1-lr3-is-there-a-difference-us-peptides-discusses-190362251.html).
IGF-1 is a peptide that acts similarly to insulin, and its main function in the body is to stimulate growth by increasing GH secretion from the pituitary gland, as well as regulating cell growth and cell death. The functioning of the pituitary gland and the hormones it secretes decreases with aging, however, IGF-1 is capable of bypassing the pituitary gland and is able to elicit the same response as GH does.