Intramuscular testosterone injections were first used around fifty years ago. Commercially available preparations contain testosterone esters in an oily vehicle. Esterification is designed to retard the release of testosterone from the depot site into the blood because the half life of unmodified testosterone would be very short. For many years intramuscular preparations were the most commonly used testosterone therapy and this is still the case in some centers. Pain can occur at injection sites, but the injections are generally well tolerated and free of major side effects. Until recently, the available intramuscular injections were designed for use at a frequency of between weekly and once every four weeks. These preparations are the cheapest mode of testosterone treatment available, but often cause supraphysiological testosterone levels in the days immediately following injection and/or low trough levels prior to the next injection during which time the symptoms of hypogonadism may return (Nieschlag et al 1976). More recently, a commercial preparation of testosterone undecanoate for intramuscular injection has become available. This has a much longer half life and produces testosterone levels in the physiological range throughout each treatment cycle (Schubert et al 2004). The usual dose frequency is once every three months. This is much more convenient for patients but does not allow prompt cessation of treatment if a contraindication to testosterone develops. The most common example of this would be prostate cancer and it has therefore been suggested that shorter acting testosterone preparations should preferably used for treating older patients (Nieschlag et al 2005). Similar considerations apply to the use of subcutaneous implants which take the form of cylindrical pellets injected under the skin of the abdominal wall and steadily release testosterone to provide physiological testosterone levels for up to six months. Problems also include pellet extrusion and infection (Handelsman et al 1997).
The testicles produce an enzyme called 11ßHSD-1 which protects your testosterone molecules from the effects cortisol.  During times of prolonged stress and chronically elevated cortisol, there simply is too much cortisol for 11ßHSD-1 to handle.  This results in testosterone molecules being destroyed inside the gonads before they even enter the bloodstream (8, 9).

So, how does one ensure that testosterone levels remain in balance? Some doctors suggest that monitoring testosterone levels every five years, starting at age 35, is a reasonable strategy to follow. If the testosterone level falls too low or if the individual has the signs and symptoms of low testosterone levels described above, testosterone therapy can be considered. However, once testosterone therapy is initiated, testosterone levels should be closely monitored to make sure that the testosterone level does not become too high, as this may cause stress on the individual, and high testosterone levels may result in some of the negative problems (described previously) seen.
The partial synthesis in the 1930s of abundant, potent testosterone esters permitted the characterization of the hormone's effects, so that Kochakian and Murlin (1936) were able to show that testosterone raised nitrogen retention (a mechanism central to anabolism) in the dog, after which Allan Kenyon's group[186] was able to demonstrate both anabolic and androgenic effects of testosterone propionate in eunuchoidal men, boys, and women. The period of the early 1930s to the 1950s has been called "The Golden Age of Steroid Chemistry",[187] and work during this period progressed quickly. Research in this golden age proved that this newly synthesized compound—testosterone—or rather family of compounds (for many derivatives were developed from 1940 to 1960), was a potent multiplier of muscle, strength, and well-being.[188]
Other side effects include increased risk of heart problems in older men with poor mobility, according to a 2009 study at Boston Medical Center. A 2017 study published in JAMA found that treatments increase coronary artery plaque volume. Additionally, the Food and Drug Administration (FDA) requires manufactures to include a notice on the labeling that states taking testosterone treatments can lead to possible increased risk of heart attacks and strokes. The FDA recommends that patients using testosterone should seek medical attention right away if they have these symptoms:
Does the diminution that age brings with it in both total and bioavailable T have any clinical significance? This question leads us to the theme of this paper, “The Many Faces of Testosterone”. If testosterone were simply a “sex hormone” involved only with sexual desire and arousal we might tend to dismiss testosterone treatment in the aging man as merely a “life-style” therapy without any substantive basis for broad physiological necessity. The fact is, however, that the sexual attributes of testosterone are the least of its physiological necessities and that testosterone has a broad spectrum of demonstrated physiological functions as well as a wide variety of physiological and pathophysiological associations about which we are just learning.
Mood disturbance and dysthymia are part of the clinical syndrome of hypogonadism. Epidemiological studies have found a positive association between testosterone levels and mood, and depressed aging males have lower testosterone levels than controls (Barrett-Connor, Von Muhlen et al 1999). Furthermore, induction of a hypogonadal state during treatment of men for prostate cancer leads to an increase in depression scores (Almeida et al 2004). Trials of testosterone treatment effects on mood have varied in outcome. Data on the effects on men with depression are conflicting (Seidman et al 2001; Pope et al 2003) but there is evidence that testosterone treatment of older hypogonadal men does result in improvements in mood (Wang et al 1996) and that this may occur through changes in regional brain perfusion (Azad et al 2003).
Epidemiological studies have also assessed links between serum testosterone and non-coronary atherosclerosis. A study of over 1000 people aged 55 years and over found an inverse correlation between serum total and bioavailable testosterone and the amount of aortic atherosclerosis in men, as assessed by radiological methods (Hak et al 2002). Increased intima-media thickness (IMT) is an early sign of atherosclerosis and has also been shown to predict cardiovascular mortality (Murakami et al 2005). Cross-sectional studies have found that testosterone levels are negatively correlated with carotid IMT in independently living men aged 74–93 years (van den Beld et al 2003), diabetic men (Fukui et al 2003) and young obese men (De Pergola et al 2003). A 4-year follow up study of the latter population showed that free testosterone was also inversely correlated with the rate of increase of IMT (Muller et al 2004).

In order to discuss the biochemical diagnosis of hypogonadism it is necessary to outline the usual carriage of testosterone in the blood. Total serum testosterone consists of free testosterone (2%–3%), testosterone bound to sex hormone binding globulin (SHBG) (45%) and testosterone bound to other proteins (mainly albumin −50%) (Dunn et al 1981). Testosterone binds only loosely to albumin and so this testosterone as well as free testosterone is available to tissues and is termed bioavailable testosterone. Testosterone bound to SHBG is tightly bound and is biologically inactive. Bioavailable and free testosterone are known to correlate better than total testosterone with clinical sequelae of androgenization such as bone mineral density and muscle strength (Khosla et al 1998; Roy et al 2002). There is diurnal variation in serum testosterone levels with peak levels seen in the morning following sleep, which can be maintained into the seventh decade (Diver et al 2003). Samples should always be taken in the morning before 11 am to allow for standardization.

One study looking at alcohol consumption found that increasing alcohol consumption led to a higher level of free & total testosterone compared to a non-drinking control group (20). Drinking did however lower SHBG testosterone levels, though this type of testosterone is bound to a protein meaning our bodies cannot use it to build muscle or increase our mood.

Now that we know chronic insulin spikes lead to lower Testosterone production, I hope I haven’t sent you running into the low carb camp! There are a few studies out there showing that long term low carb or ketogenic dieting leads to higher cortisol levels (especially with subjects who are training), and decreased testosterone levels (28 & 29). I have used low carb diets in the past with successful results (winning a national bodybuilding title), however the key is to use cyclical carb re-feeds. If you’re going to go on a low carb diet for whatever reason, be sure to work in a large carb reefed once a week.
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