Low testosterone may be caused by a failure of the testicles (testes) to make enough testosterone. Low testosterone may be present at birth or it may develop later in life. However, there are other potential causes of low testosterone. Testosterone also has effects on sexual function. If your testosterone levels are less than 12 nmol/L and you have symptoms, you may benefit from testosterone replacement therapy (TRT). For starters, a healthy sex life is important in regulating your sex hormone and testosterone levels. Millions of American men use a prescription testosterone injection or gel as forms of testosterone replacement therapy (often referred to as TRT therapy) to restore normal levels of the manly hormone. Late-onset male hypogonadism happens when the decline in testosterone levels is linked to general aging and/or age-related conditions, particularly obesity and Type 2 diabetes. Lower-than-normal testosterone levels typically only cause symptoms in males. As testosterone in your blood increases, it suppresses the production of gonadotropin-releasing hormone, which helps maintain normal levels of testosterone. For women, testosterone therapy has a much narrower evidence-based use case, and treatment should remain within the female physiologic range rather than approach male-style replacement targets (Mulhall et al., Journal of Urology, 2018; Davis et al., Journal of Sexual Medicine, 2019). For men who’ve always prided themselves on physical strength or athletic performance, testosterone decline can be particularly devastating. This isolation can worsen depression and anxiety symptoms, creating a downward spiral. In the workplace, low testosterone can manifest as decreased motivation, reduced competitive drive, and difficulty making decisions. The brain has testosterone receptors throughout areas responsible for mood, cognition, and motivation. Men may experience decreased libido, difficulty achieving or maintaining erections, and reduced sexual satisfaction. But that is a diagnostic threshold, not a universal treatment target. This is why guidelines talk more about physiologic replacement and appropriate monitoring than about one universal "optimal" number. A man using injections measured at trough will not necessarily show the same lab value as a man using transdermal therapy measured under a different protocol. If you search for testosterone targets on TRT, you will usually find a chart, a clinic range, or a single number presented as the answer. "You shouldn't focus too narrowly on nonspecific symptoms or a test result. This is not about a temporary infection but low-grade inflammation that affects the body over time. Look for providers who specialize in men’s health and hormone therapy. Not all healthcare providers have extensive experience with testosterone treatment. At Performance Center for Men, our comprehensive evaluation process ensures we identify not just testosterone deficiency but any underlying factors contributing to your symptoms. A comprehensive testosterone evaluation should include detailed medical history, physical examination, and laboratory testing. Some people may experience a decline in sex drive as they get older, but those with low testosterone will likely experience a more drastic drop. Some doctors may prescribe testosterone off-label to females to improve libido, but this use has not been approved by the Food and Drug Administration (FDA). Symptoms can be subtle, but treatment may help if the symptoms affect your lifestyle. Males may experience low testosterone as they get older or due to some health conditions. The evidence also points to the importance of regular follow-up, frequently within the first year after the start of treatment and less stringent thereafter but uninterrupted for the duration of treatment.