Doctor-prescribed sermorelin HGH therapy sermorelin HGH therapy works best for those adults in the borderline area between normal HGH levels and growth hormone deficiency. An appropriate age range would be in one’s thirties and forties. This is when growth hormone levels are decreasing. HGH production peaks during puberty to stimulate growth. By the time a person reaches his or her mid-twenties, the amount of HGH secreted each day begins to decline. Although most people will not notice symptoms of HGH deficiency in their thirties, changes are taking place beneath the skin’s surface. That is why the thirties and forties are the best time to optimize HGH production – whether through natural lifestyle changes or sermorelin therapy.