Hypogonadism (reduced testicular function) has numerous negative health consequences for men. Left untreated, testosterone deficiency leads to infertility, impotence, weight gain, cardiovascular disease, osteoporosis and depression. Testosterone replacement therapy is indicated for men with proven low testosterone in order to maintain secondary sex characteristics and control symptoms of hypogonadism. There are several different ways of administering testosterone � intramuscular, transdermal, sublingual, buccal (in the mucous membrane of the cheeks). What all these options have in common is that they avoid the gastrointestinal tract. This is because taking it in tablet form causes it to be rapidly deactivated in the liver and renders it ineffective. In Bulgaria, the most available intramuscular testosterone is in the form of testosterone esters or testosterone undecanoate. In the first case, it is applied once every 14 to 21 days, and in the second – every 3 months. Contraindications for starting testosterone therapy are: Immediate reproductive desires � testosterone suppresses normal sperm production; High hematocrit levels; In men with breast or prostate cancer; Men with a palpable prostate nodule; Prostate-specific antigen (PSA) levels > 4 ng/ml or > 3 ng/ml and high risk for prostate cancer (eg, family history); Severe untreated sleep apnea; Severe heart failure; Experienced myocardial infarction or stroke in the previous 6 months; Thrombophilia; Before starting testosterone replacement therapy, especially in men over the age of 50, PSA should be tested and a urologist should be consulted to rule out a prostate mass. After initiation of therapy, PSA monitoring is required 3 to 12 months after treatment. Re-consultation with a urologist is necessary if within the first 12 months there is an increase in PSA by more than 1.4 ng/ml compared to the baseline or reaches levels above > 4 ng/ml. Symptoms of hypogonadism were assessed 3-12 months after initiation of therapy and annually thereafter. Treatment with testosterone esters has more labile symptom control because serum testosterone levels have wide variations, whereas testosterone undecanoate has a more stable action profile. Testosterone levels are monitored in the first 3-6 months, then once a year. They aim to be in the middle of the norm. The hematocrit is examined 3-6 months after the start of therapy and then once a year. If it rises >54%, therapy should be discontinued until it normalizes. It can then be resumed at a lower dose. In men with osteoporosis, follow-up of bone density of lumbar vertebrae and/or femoral neck is recommended 1-2 years after the start of therapy. Benefits of the therapy Secondary birthmarks. In young men who have not reached puberty, testosterone therapy leads to the development of secondary sexual characteristics – facial hair, voice loss,accumulation of bone and muscle mass, penis enlargement. In men with proven low testosterone levels, there is an improvement in libido and sexual function. Testosterone has no effect in men with normal testosterone. In these cases, 5-alpha reductase inhibitors (eg sildenafil) are recommended. Testosterone replacement therapy improves self-esteem and depressive symptoms. It also increases physical potential and the accumulation of muscle mass. It significantly improves the ratio of muscle to fat tissue and, accordingly, the metabolic profile. In men with hypogonadism and osteoporosis, there may be an improvement in bone density. When there is a high fracture risk, however, additional treatment specific to osteoporosis is warranted. Negative effects of testosterone administration: Acne and oily skin; Erythrocytosis; Detection of subclinical prostate carcinoma and growth of metastatic tumors; Decreased spermatogenesis and fertility; Gynecomastia or development of mammary gland carcinoma; Baldness; Provoking or worsening existing sleep apnea; References Shalender Bhasin, Juan P Brito, Glenn R Cunningham, Frances J Hayes, Howard N Hodis, Alvin M Matsumoto, Peter J Snyder, Ronald S Swerdloff, Frederick C Wu, Maria A Yialamas, Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline, The Journal of Clinical Endocrinology & Metabolism, Volume 103, Issue 5, May 2018, Pages 1715�1744, https://doi.org/10.1210/jc.2018-00229