HCG is another hormonal substance that is often used along with TRT. TRT helps to raise testosterone levels in men. However, HCG helps boost testosterone production and keep it at an optimal level. HCG also helps to reduce the side effects caused by TRT. Hence, you may only need HCG if you want to have children in the future; this is because TRT reduces Luteinizing Hormone production (which aids the production of sperm and testosterone). But if you use HCG while on testosterone, it would aid sperm production, reduce side effects of TRT, and help reduce testicular shrinkage.