I would like to share some scientific info on the common and differences on the Somedin IGF1-lr3 which is widely marketed for athletes, and Increlex which is a IGF1 product prescribed to children who suffer from a condition called severe primary IGF-1 deficiency.
Increlex contains IGF1 that is identical to the human endogenous IGF1 , while the IGF1-lr3 is a configuration of the IGF1 molecule. The LR3 stands for an addition of a "tail" added in a certain formation to the IGF1 molecule, this makes the IGF1-lr3 much more potent.
For a brief explanation (refer to https://www.ncbi.nlm.nih.gov/pubmed/18567600) - The actions of IGF-1 in vivo are modulated by IGF-1 binding proteins (IGFBPs), which generally act to inhibit IGF-I signalling. the analogue of IGF-I (LR IGF-I) has a significantly reduced binding affinity for IGFBPs. In simple words most of the IGF1 in the body is bounded to binding proteins (same as u probably know is testosterone and other hormones) which makes it non active, The new configuration in the Somedin helps it travel in its active form in the serum and activates its receptors much much more effectively. As you may check in a simple google search on the Incralex it requires much higher dosages - a kid may require 12000mcg a day (like 150 times higher dosage then a 240lbs athlete may need)
Now anyone may ask himself - why then the prescribed IGF1 is not IGF1-lr3 then ? - I'm not an expert for this subject but I may speculate, a very based speculation, that making a drug to a prescribed drug simply requires the investment of great deal of resources and tedious 3 phases of clinical trials, while there are very few kids who are prescribed with IGF1 (the only ones to get this med are the ones who has a mutation in their GH receptor (rare) so GH conventional treatment doesn't work on them)