Somatropin is the man-made version of human growth hormone. Each manufacturer of somatropin assigns its own brand name, such as Genotonorm, Saizen, Genotropin, Humatrope, Nutropin and Norditropin. They are available only by prescription and administered by injection.
HGH is produced at a rate that peaks during adolescence, at time when normal growth is accelerated. The production of HGH decreases with age, 14% each year on average. Humans normally produce about 500 micrograms of HGH daily at age 20. By age 80, the daily production falls to 60 (or less) micrograms. Many doctors consider IGF-1 levels sub 350 to be HGH deficient.