The effect excess testosterone has on the body depends on both age and sex. It is unlikely that adult men will develop a disorder in which they produce too much testosterone and it is often difficult to spot that an adult male has too much testosterone. More obviously, young children with too much testosterone may enter a false growth spurt and show signs of early puberty and young girls may experience abnormal changes to their genitalia. In both males and females, too much testosterone can lead to precocious puberty and result in infertility. 
Testosterone [Figure 1] is the main male sex hormone. It is responsible for male sexuality and is the main hormone-producing the features associated with masculinity such as substantial muscle mass, facial hair, libido, and sperm production.[1] Besides, the hormone has other vital functions as the basic chemical composition of testosterone is steroidal; and steroids are known to have significant physiological, as well as psychological, effects in male individuals, especially adults.[1] Testosterone production is reduced gradually in men starting from the age of 30.[2] Hence, testosterone blood concentrations slowly diminish as age progresses. As a result, men may experience a number of physiological and psychological events, such as a lack of sex-drive, erectile dysfunction, acute depression, fatigue, low energy levels, and insomnia.[3]

Like other supplements and medication, testosterone therapy comes with risks and possible side effects. This is particularly true if you try to take it for normal aging rather than for treatment of a condition. Also, the Cleveland Clinic points out that the effects that these supplements may have on your heart and prostate can lead to a number of potential issues. Complications include:
This summary is intended for general informational purposes only, and should not be interpreted as specific medical advice. The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of purity, strength, or safety of the products. As a result, effects may vary. You should read product labels. In addition, if you are taking medications, herbs, or other supplements you should consult with a qualified healthcare provider before taking a supplement as supplements may interact with other medications, herbs, and nutritional products. If you have a medical condition, including if you are pregnant or nursing, you should speak to your physician before taking a supplement. Consult a healthcare provider if you experience side effects.
Cross-sectional studies conducted at the time of diagnosis of BPH have failed to show consistent differences in testosterone levels between patients and controls. A prospective study also failed to demonstrate a correlation between testosterone and the development of BPH (Gann et al 1995). Clinical trials have shown that testosterone treatment of hypogonadal men does cause growth of the prostate, but only to the size seen in normal men, and also causes a small increase in prostate specific antigen (PSA) within the normal range (Rhoden and Morgentaler 2005). Despite growth of the prostate a number of studies have failed to detect any adverse effects on symptoms of urinary obstruction or physiological measurements such as flow rates and residual volumes (Snyder et al 1999; Kenny et al 2000, 2001). Despite the lack of evidence linking symptoms of BPH to testosterone treatment, it remains important to monitor for any new or deteriorating problems when commencing patients on testosterone treatment, as the small growth of prostate tissue may adversely affect a certain subset of individuals.
Epidemiological evidence supports a link between testosterone and glucose metabolism. Studies in non-diabetic men have found an inverse correlation of total or free testosterone with glucose and insulin levels (Simon et al 1992; Haffner et al 1994) and studies show lower testosterone levels in patients with the metabolic syndrome (Laaksonen et al 2003; Muller et al 2005; Kupelian et al 2006) or diabetes (Barrett-Connor 1992; Andersson et al 1994; Rhoden et al 2005). A study of patients with type 2 diabetes using measurement of serum free testosterone by the gold standard method of equilibrium dialysis, found a 33% prevalence of biochemical hypogonadism (Dhindsa et al 2004). The Barnsley study demonstrated a high prevalence of clinical and biochemical hypogonadism with 19% having total testosterone levels below 8 nmol/l and a further 25% between 8–12 nmol/l (Kapoor, Aldred et al 2007). There are also a number longitudinal studies linking low serum testosterone levels to the future development of the metabolic syndrome (Laaksonen et al 2004) or type 2 diabetes (Haffner et al 1996; Tibblin et al 1996; Stellato et al 2000; Oh et al 2002; Laaksonen et al 2004), indicating a possible role of hypogonadism in the pathogenesis of type 2 diabetes in men. Alternatively, it has been postulated that obesity may be the common link between low testosterone levels and insulin resistance, diabetes and cardiovascular disease (Phillips et al 2003; Kapoor et al 2005). With regard to this hypothesis, study findings vary as to whether the association of testosterone with diabetes occurs independently of obesity (Haffner et al 1996; Laaksonen et al 2003; Rhoden et al 2005).
Testosterone functions within the brain. There are several lines of evidence for this: there are androgen receptors within the brain; testosterone is converted to both dihydrotestosterone (DHT) and estradiol by the actions of 5-α-reductase and aromatase respectively in the brain; steroid hormones promote neuronal cell growth and survival (Azad et al 2003). Testosterone enhances cerebral perfusion in hypogonadal men and that perfusion takes place specifically in Brodman areas 8 and 24, regions of the brain that are concerned with: strategic planning, higher motor action, cognitive behaviors, emotional behavior, generalized emotional reaction, wakefulness and memory (Greenlee 2000; Azad et al 2003). Studies of cognition demonstrate that older men with higher levels of free testosterone index (a surrogate measure of bioavailable testosterone) have better scores in tests of: visual memory, verbal memory, visuospatial functions and visuomotor scanning. Hypogonadal men have lower scores in tests of memory, visuospatial function, with a faster decline in visual memory (Moffat et al 2002). In a very small, short term placebo-controlled study hypogonadal men with Alzheimer’s Disease (AD) treated with testosterone demonstrated a modest improvement in a cognition assessment score in AD (Tan and Pu 2003).
Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.[77] The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.[77] Thus it is the challenge of competition among males of the species that facilitates aggression and violence.[77] Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.[77] The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males.[77]

Bhatia et al (2006) studied 70 male patients with type2 diabetes mellitus (age range 24–78 years). Thirty-seven subjects were found to have hypogonadism based on a calculated free testosterone level of less than 6.5 μg/dl. The hypogonadal group had a statistically significant lower hematocrit. Anemia was observed in 23% of the patients (16 out of 70). In 14 of 15 anemic patients calculated free testosterone was low.
There are three categories of healthy fat. Number one is healthy saturated fat. The truth about saturated fat is it’s actually good for you if it’s the proper kind. Healthy saturated fat is found in coconut oil and raw, fermented dairy products like goat milk kefir, yogurt, or raw goat or sheep milk cheese. However, avoid conventional dairy because it will actually damper your testosterone.
It is hard to know how many men among us have TD, although data suggest that overall about 2.1% (about 2 men in every 100) may have TD. As few as 1% of younger men may have TD, while as many as 50% of men over 80 years old may have TD. People who study the condition often use different cut-off points for the numbers, so you may hear different numbers being stated.
TT may help you but it may have adverse (harmful) results. (See discussion of these side effects below.) The Federal Drug Administration (FDA) has said that testosterone drug labels should state that there is a risk for heart disease and stroke for some men using testosterone products. All men should be checked for heart disease and stroke before, and periodically while on, TT. The AUA however, on careful review of evidence-based peer review literature, has stated that there is no strong evidence that TT either increases or decreases the risk of cardiovascular events.

The largest amounts of testosterone (>95%) are produced by the testes in men,[2] while the adrenal glands account for most of the remainder. Testosterone is also synthesized in far smaller total quantities in women by the adrenal glands, thecal cells of the ovaries, and, during pregnancy, by the placenta.[126] In the testes, testosterone is produced by the Leydig cells.[127] The male generative glands also contain Sertoli cells, which require testosterone for spermatogenesis. Like most hormones, testosterone is supplied to target tissues in the blood where much of it is transported bound to a specific plasma protein, sex hormone-binding globulin (SHBG).
If a young man's low testosterone is a problem for a couple trying to get pregnant, gonadotropin injections may be an option in some cases. These are hormones that signal the body to produce more testosterone. This may increase the sperm count. Hedges also describes implantable testosterone pellets, a relatively new form of treatment in which several pellets are placed under the skin of the buttocks, where they release testosterone over the course of about three to four months. Injections and nasal gels may be other options for some men.