The amount of testosterone synthesized is regulated by the hypothalamic–pituitary–testicular axis (see figure to the right). When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the hypothalamus, which in turn stimulates the pituitary gland to release FSH and LH. These latter two hormones stimulate the testis to synthesize testosterone. Finally, increasing levels of testosterone through a negative feedback loop act on the hypothalamus and pituitary to inhibit the release of GnRH and FSH/LH, respectively.
There have been a number of smaller studies on men receiving testosterone-replacement therapy, and if you look at the results cumulatively, the rate of prostate cancer in these men was about 1% per year. If you look at men who show up for prostate cancer screening, same sort of age population, the rate tends to be about the same. You have to be cautious in comparing studies and combining the results, but there’s no signal in these results that testosterone-replacement therapy creates an unexpectedly high rate of prostate cancer.
Testosterone may decrease your chances of Alzheimer’s Disease. Several studies have linked low testosterone levels to an increased risk of Alzheimer’s disease. In a 2010 study by the University of Hong Kong, researchers studied 153 Chinese men who were recruited from social centers. They were at least 55 years and older, lived in the community, and didn’t have dementia. Of those men, 47 had mild cognitive impairment — or problems with clear thinking and memory loss.
In the last few years, a lot of men and women have switched over to a pellet that goes under your skin. This is probably the best way to take testosterone now. The pellet is life-changing for both men and women (the dose for women is much lower than it is for men). Women, you won’t get bulky and grow a beard when you take testosterone to achieve normal levels, but you will probably lean out a little without losing your curves, and your energy and sex drive will be amazing. Female bodybuilders who experience weird scary side effects are taking anabolic steroids.