According to Harvard Medical School, males use hormone replacement therapy in order to treat very low levels of testosterone, which has been linked to low mood, fatigue and diminished muscle mass. Harvard notes that some men find this more effective than synthetic testosterone.
According to Harvard Medical School, male testosterone level typically peaks at the age of seventeen. Testosterone levels decline naturally post-adolescence, but some men experience hypogonadism due to problems in their testes or pituitary glands that makes hormone levels unnaturally low. Testosterone is typically replaced via a gel that is rubbed into the skin on the abdomen, upper arms and shoulders. There is also a gel designed to be spread on the gums. Testosterone cannot be safely replaced via a pill because it can be toxic to the liver. Patches applied to the skin serve as an alternative delivery method.
Harvard notes that male hormone replacement may have negative side effects. Hormone injections make blood thicker and more likely to clot. Hormone replacement therapy does not directly spread cancer, but men who already have prostate cancer and receive hormone replacement therapy may be at risk of waking up dormant cancer cells with the injections of testosterone. Harvard notes that positive side effects include making men leaner and more interested in sex, though hormone replacement therapy cannot directly treat erectile dysfunction.