Bio 101: What does testosterone therapy do to your body?

steroid biosynthesis

From high school biology you probably know testosterone (as opposed to estrogen) is the male hormone. It’s what separates (quite literally) the men from the boys. Women have around 7 times less serum (blood) testosterone flowing inside of their veins. And of course, cheaters overzealous body builders use it to quickly gain muscle mass.

Testosterone is a catabolic steroid hormone responsible for most male characteristics. The androgen is thought to be crucial to development for male reproductive tissues (e.g. testes and prostate) and post-pubescent sexual characteristics (increase in bone density, more body hair, and muscle growth).


As men age, testosterone levels decrease; but if older men are injected with testosterone to boost their serum concentrations to levels comparable to younger men, research by Urban et al. from the Department of Internal Medicine of University of Texas Medical Branch in Galvesto indicates that the older men experience significantly increased strength and muscle growth.

Katznelson et al. from the Neuroendocrine Unit of Massachusetts General Hospital in Boston also found that men who had acquired hypogonadism responded to testosterone treatment. Hormone therapy significantly reduced bone modeling but increased trabecular (the spongy internal structure) bone density. Testosterone treatment also decreased body fat while increasing lean muscle mass. The numbers are a bit astounding; on average men loss 14% body fat (plus/minus 4%, P < 0.001) and gained 7% muscle mass (plus/minus 2%, P = 0.01).

vial testosterone

tl;dr–There’s good reason testosterone is (illegally) supplemented in athletic events. Without additional training, it significantly boosts lean muscle growth at the expense of fat. Unbelievable. With a few injections, you drop 14% body fat and gain 7% lean muscle mass. Caveat: its forbidden in athletic competition and looked down on.

Coming soon: How do I boost testosterone without hormone therapy?

Source 1, 2, 3, 4, 5



Pastry Chef (, software engineer (, and fitness enthusiast.

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1 Response

  1. Paulette Karpf says:

    This medical bone density is not the true physical “density” of the bone, which would be computed as mass per volume. It is measured by a procedure called densitometry, often performed in the radiology or nuclear medicine departments of hospitals or clinics. The measurement is painless and non-invasive and involves low radiation exposure. ”..”

    Most interesting brief article on our online site

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