HCG stimulates your natural production of testosterone. It mimics the LH (luteinizing hormone) signal from the pituitary gland.
Under normal conditions your body regulates your hormone levels via the HPTA - hypothalamic-pituitary-testicular axis. It’s basically your body’s feedback system that determines when your testosterone is low and increases production (increases LH) … then when the levels rise, decreases production (decreases LH). When you are young and in good health it is – perfection. It regulates everything perfectly and all is right with the world.
When you introduce testosterone into your body, you are messing with the HPTA. Your body sees the excess testosterone and shuts off natural production (LH ~ 0). If you keep introducing testosterone, your natural production is pretty much shut down during this period.
So … your testicles begin to shrink – they atrophy. Your testicles will reduce in size. In some cases the size reduction may be drastic (I guess it depends on how large your testicles were in the first place). Ejaculatory volume may also decrease.
If you would like your natural production to resume, leaving your testicles shut down indefinitely is probably not a good plan. Let’s say you were on TRT for 5 years and never used HCG. You would be shut down for 5 years. If you tried to re-start natural production … it could be tough. Basically, your ability to produce testosterone may be severely diminished.
When you are older (say in your 50s), you don’t produce much testosterone anyway. So whether or not your natural production comes back may not matter. In my case, the testicles are not doing much anyway.
When I take HCG, my testicles increase in diameter a little bit. Ejaculatory volume increases a just little bit. Basically, HCG can be like mashing the gas pedal to the floor on your natural production (especially if you take large enough doses of HCG). In my case, it’s like mashing the gas on a worn out 1972 Chevy Vega – not much happens.
For younger folks, being shut down can effect fertility. If you still want kids, you probably want to have access to some HCG. Like anything else, there are some down sides to HCG. For example, HCG can make it more difficult for you to control estrogen levels (it typically causes some additional aromatization). Some folks have enough trouble getting the estrogen levels in the right range – without HCG in the mix. Adding HCG can definitely complicate the protocol.
This should be enough information to get you started. I’m sure other folks can chime in with more prod and cons.