Patients who have been injected or taken testosterone (androgen) to help enhance their libido are often among the people who visit the clinic. They treat testosterone as a man’s elixir of immortality, believing that as long as androgens are supplemented, men will not age, their virility will not diminish, and their fertility will not decline. But is this really the case? There are two sides to everything, there is a favorable side and a negative side. Testosterone is no exception, it is a double-edged sword, the right use can play an unexpected effect, the use of improper lead to irreparable end. Testosterone is produced by the testicles and is present in the body throughout the various stages of a man’s life. It maintains normal sexual differentiation during the embryonic period prior to male birth, stimulates the differentiation of Wolffian’s duct into the male reproductive duct, and is closely associated with prostate, penis and scrotal development. Disorders of testosterone synthesis or receptor dysfunction can cause abnormal fetal sexual differentiation, e.g., male pseudohermaphroditism, hypospadias, cryptorchidism, etc. Puberty promotes development. After puberty begins, testosterone promotes the development of male gonads and sexual characteristics and accelerates the growth of bones and muscles, forming the male physique and hair distribution; it makes the seminal vesicles and prostate gland develop. If androgen deficiency occurs in boys during development, they will develop anaplasia or eunuch-like physique. It promotes and maintains spermatogenesis and enhances libido as we age. Testosterone is essential for penile growth during fetal, childhood and pubertal development. Decreased androgens can lead to decreased libido and even impotence in men; there can also be a decrease in sperm count or absence of sperm, and can also lead to feminization of the man’s breasts. Decreased beard, etc. Middle-aged men with low testosterone not only have a decline in sexual performance, but also have an emotional and mental state, mainly manifested as inattentiveness, depression, agitation, poor communication, lack of interest in things that used to interest them, easy sweating, insomnia, etc., also known as “male menopause”. At this time, if testosterone is properly supplemented, many symptoms will be reduced or disappear, which will help middle-aged men to go through menopause smoothly. All of the above are the effects and advantages of endogenous testosterone (produced in the body), but does exogenous testosterone have the same effect? Many clinical studies and real-life medical records show that long-term supplementation with large amounts of testosterone does not achieve the results we want. Exogenous testosterone does not penetrate the blood-testis barrier and affect the function of the testes themselves. Long-term application of large amounts of testosterone causes testosterone to reach a certain level in various tissues in the body, which inhibits the secretion of luteinizing hormone, thus inhibiting the secretion of testosterone in the testes, affecting spermatogenesis and leading to oligospermia or azoospermia. In severe cases, testicular atrophy or even disappearance occurs. It is common to see patients with testicular atrophy due to long-term testosterone application in clinical practice. Long-term application of testosterone increases the incidence of prostate cancer and increases the symptoms of patients with prostate enlargement. It increases the risk of vascular embolism and increases the incidence of cardiovascular disease due to the effect on lipid metabolism and increased blood cell pressure, and can worsen the condition of patients with respiratory sleep apnea syndrome. How can testosterone be used well in the clinic? Then a professional physician is needed to guide the use of the medication. For patients with small congenital testicular and genital development, you can try to apply testosterone to promote the development of secondary sexual characteristics. For patients with low laboratory serum testosterone can be supplemented with testosterone for a short period of time, which has achieved the purpose of promoting libido, thus increasing the patient’s confidence and desire for sexual life, and to a certain extent may achieve to stimulate the production of their own testosterone. Patients with orchiectomy can be supplemented with testosterone for a long time to maintain secondary sexual characteristics and sexual function. Before applying testosterone the patient’s condition should be evaluated, whether the patient is at risk of developing cardiovascular disease, whether the patient has the presence of respiratory sleep apnea syndrome, men over 45 years of age must be tested for prostate-specific antigen (PSA) to discharge the possibility of prostate cancer, and for patients with prostate enlargement should weigh the pros and cons, and must grasp that the benefits outweigh the disadvantages before applying. Finally, a word of caution: never take androgens (testosterone) as a sex drug or as a man’s elixir of immortality. If you think you may need androgen supplementation, it is best to seek the advice of a doctor at a hospital.