IGF is naturally produced in the liver as a result of GH (growth hormone) metabolism in the presence of insulin. Muscle tissue can also produce IGF-1 by way of an intracellular response. In fact, one of the benefits of training sets that result in an intense burn , or stretch position training , is the production of natural IGF-1. It is also a side effect of oral 17-Alfa Alkylated steroids, which cause a higher release of IGF-1 from the liver. IGF-1 receptors exist throughout muscles and organs such as the heart, spleen, small intestines and kidneys with a higher concentration of receptors existing effects upon organs. IGF-1 is extremely anabolic, more so than GH or insulin.
Recombinant IGF-1 (genetically engineered) was reported effective when injected intramusculary because it causes localized growth. This was the most popular method, and agreed the wisest for the most part.The drug has a half life of about ten minutes, and if it has been bound to IGF-BP3 (binding protein) the half life is extended to 12 hours. Pros often stack Insulin and or GH with IGF-1 because IGF-1 shuts off natural GH production and GH causes insulin resistance and interracts with Insulin. But this would actually be an untrue term for IGF-1.
IGF-1 can have all the side effects of GH or insulin use with an added negative: Gastrointestinal growth. This is due to the high number of IGF-1 receptors in the GI tract as compared to skeletal muscle. The latter has more GH receptors. The explains much of the bloat of pro bodybuilders.
IGF-1 is not stable in synthetic forms. A loud noise, shaking a vial and sudden heat changes can render it nothing more than expensive Amino Acids.Picture a piece of string folded up in a specific shape and held in that shape by a few fibers. This is what an amino acid sequence for GH or IGF-1 looks like,but the IGF-1 sequence has only 2 fibers keeping the active shape. The strand or string is a specific amino acid sequence. The shaping fibers holding the active shape are called disulfide bridges. Changing the folding or break a bridge and the IGF-1 no longer fits into it's receptor site. Like a key to a lock a drug must have the right shape to actuate it's receptor. Again this explains the necessity of careful preparation and site specific injection (into the musle group trained that day) when IGF-1 was administered.
Common Stacks have been 0.25-0.50 of GH per KG of bodyweight stacked with 60-1000mcg of IGF-1 divided into 2-5 daily injections. Many have reported improved lean mass gains by combining both with insulin and high androgen AAS (d-bol, anadrol) for 4-8 weeks. Many simply injected 40-mcg of IGF-1 into the muscle group trained that day after training. It is important to note that IGF-1 can cause hypoglycemia and blood sugar monitoring is considered paramount.
The reader should note that IGF-1 has been used clinically on children at dosages of over 3000-7000 mcg a day! No negative sides were reported though none were expected. The point being is that 40-100mcg of IGF-1 used by athletes is most likely insufficient yet very expensive, However the results some individuals have realized through IGF-1 have been amazing.