I've been asked many times by customers how really GH effects the body ? Many also are interested to know for how long it's effective to use GH ? if one has a limited budget is good to use for several weeks ?
The GH-IGF1 is possible the most complex hormonal axis in the human body. I'll try to offer some science based yet simple answers in a nutshell.
GH has a direct and immediate metabolic effects - it releases glucose and fatty acids to the circulation, meaning it takes stored energy and make it available for the different organs and tissues, this is how it increases metabolism and burns fat both directly (taking fat stored fat and turning it to free fatty acids) and indirectly by expending calories and energy consumption. Note that releasing glucose to the circulation requires the body to secrete insulin immediately in order to balance the glucose levels and lower them back to normal, this mechanism leads with time to decreased insulin sensitivity, as when taking superpharmacological levels of GH the body needs to secrete constantly relatively high amounts of insulin. So GH increases insulin levels and decreases insulin sensitivity (which may bring to insulin resistance in extreme cases - diabetes)
GH has a direct and immediate anabolic effect in the body - it causes different tissues (above all muscle) to retain nitrogen which leads to a positive nitrogen balance = anabolism. It also causes the body to retain minerals (sodium, potassium, calcium, phosphorus) as part of its anabolic effect as well, which explains the quite noticeable and fast water retention many users experience with GH.
Having said and explained that many of the muscle building properties of GH are mediates by IGF1 which is considered the most anabolic hormone in the body. Even if we block somehow the IGF1 secretion which is induced by GH it'll still retain some of its anabolic and metabolic effects directly through GH receptors in different tissues, but big portion of the effect will be abolished, this is why in rare condition when short statue children don't respond well to GH treatment they're given with IGF1. The GH causes IGF1 secretion from target organs such as the liver and kidneys, and the IGF1 travels in the serum to different tissues (endoctine effect). The GH also causes a local section of IGF1 (and other growth factors) on different tissues, mainly on muscle tissue, it's called autocrine effect, and it's responsible on the stimulation of cell division, and this explains some of the unique so desired effect of GH (and IGF1).
While the direct anabolic effects of GH are quite immediate (though not as prominent as the effects of anabolic steroids), the autocrine effects takes time and requires constant exposure to effective dosages.
GH has another important effect - it directly triggers fibroblast activity, which means recuperation and creation of connective tissue, this of course enables optimal recuperation from injury, but of course enables better strength=muscle gains with time. This phenomena takes also much time to be pronounced as connective tissue is the slowest to be build and/or recuprate.
The GH is used in the medical field as a short term anabolic aid for post trauma/surgery/severe-burns so yes short term of a couple of month certainly has its benefits, and will create some new muscle fibers to some extent, but as athletes knows GH really shines in long term usage