The central male hormone
Testosterone is the most important male sex hormone. Produced in the testicles, it influences muscle growth, libido, fat distribution, mood, bone density, energy levels, and much more. It significantly contributes to physical performance and mental stability . With increasing age, testosterone levels decline by about 1% per year, often due to stress, an unhealthy lifestyle, and hormonal imbalances.
When testosterone levels are too low, it is called hypogonadism . This can have a primary cause (in the testicles themselves) or a secondary cause (due to problems in the hypothalamus or pituitary gland). Symptoms range from loss of libido, erectile dysfunction, fatigue, and muscle loss to mood swings. The diagnosis can be made when low testosterone levels (< 12.1 nmol/L) are found in at least two independent blood tests performed in the morning, in combination with corresponding symptoms.
Also important: SHBG (see SHBG article) determines how much testosterone is biologically available. A high total testosterone level alone does not provide certainty if the free fraction is too low. Typically, total testosterone and free testosterone are measured.
Testosterone enanthate: Common injection form in replacement therapy
In cases of confirmed testosterone deficiency, testosterone enanthate , a long-acting ester of testosterone, can be used. It is administered intramuscularly, typically every 1–2 weeks at a dose of 125–250 mg. The ester ensures a slow release into the bloodstream, allowing for stable levels to be achieved over a longer period.
Effects: Testosterone enanthate acts like the body's own testosterone, increasing muscle strength, libido, energy, and fat loss. Side effects such as increased estrogen and DHT levels, mood swings, and skin problems are also possible, which is why regular monitoring of PSA and hematocrit levels, as well as other lab values, is essential.
Testosterone replacement therapy (TRT): Think responsibly, start individually
Transient hormone replacement therapy (TRT) can be medically beneficial in cases of diagnosed hypogonadism. International guidelines recommend TRT when symptoms are present and laboratory tests show low hormone levels. An important prerequisite is the exclusion of contraindications, such as prostate cancer, breast cancer in men, untreated sleep apnea, or elevated hematocrit (polycythemia).
The goal is to restore testosterone levels to normal physiological ranges, alleviate symptoms, and improve quality of life. Effects often become apparent within weeks (e.g., libido) to months (muscle growth). However, testosterone replacement therapy (TRT) is not a lifestyle choice , but a medically supervised therapy with essential regular checkups.
Testosterone gel: A skin-effective alternative to injections
Gel-based testosterone preparations offer the possibility of transdermal application , usually daily. Advantage: more consistent levels without sharp spikes. Disadvantage: risk of transmission to close contacts such as partners or children through direct skin contact. Regular blood tests, such as PSA and hematocrit measurements, are also necessary with gel therapy.
Testosterone deficiency: Symptoms, causes & treatments
Testosterone deficiency can be caused by age-related decline, chronic stress, overtraining, and hormonal imbalances (e.g., SHBG, DHEA, estrogen). Symptoms include loss of libido, erectile dysfunction, fatigue, muscle loss, depressed mood, difficulty concentrating, and increased body fat.
Important: Men should seek medical evaluation with a comprehensive laboratory profile (testosterone, SHBG, estradiol, LH, FSH, prolactin) if they experience corresponding symptoms or suspect a problem.
Testosterone test: How the test works
The testosterone test is performed via blood draw, usually between 7 and 10 a.m. (peak time), ideally on an empty stomach. The test typically measures total testosterone and free testosterone (often calculated).
The result is interpreted in the context of the clinical presentation and other laboratory values, such as SHBG, LH, and FSH. In unclear cases, measurements on several days are recommended for a comprehensive assessment.
TSH: Thyroid function regulation and effect on testosterone
Thyroid-stimulating hormone (TSH) regulates the thyroid gland and thus indirectly influences metabolism, energy production, and testosterone availability. Untreated hypothyroidism (high TSH, low fT3/fT4) can contribute to testosterone deficiency because it affects LH and SHBG. Therefore, TSH and fT4 should be part of the standard diagnostic workup in every hormone panel .
Triglycerides: Fat metabolism & heart health
Blood triglycerides reflect fat metabolism. High levels are often associated with insulin resistance, increased abdominal fat, and lower SHBG. Optimal triglyceride levels (< 150 mg/dL) correlate with a healthy testosterone profile, better vascular function, and reduced inflammatory response. Men with elevated triglycerides are more likely to suffer from low testosterone and erectile dysfunction.
Tip: Test your testosterone with the TRT check from Adon Health
Anyone who suspects testosterone deficiency, for example due to loss of energy, libido problems, muscle atrophy or low mood, will find a sound and discreet solution with the TRT-Check from Adon Health :
- Convenient blood test from home : Determination of total and free testosterone, SHBG, PSA, LH.
- Medical interpretation of values via video call with cooperating physicians.
- From diagnosis to therapy : If necessary, medically supervised testosterone replacement therapy (TRT).
- Ideal for men who take symptoms seriously and want to take targeted action.
Podcast on the topic of testosterone & TRT
Episode #61 of the podcast “Men’s Health” :
“ Understanding Testosterone: Nutrition, Genes & Blood Values ”, here Dr. Jonathan Apasu & Andreas Scholz explain, among other things, the role of SHBG, free testosterone and when TRT can be useful → practical, scientifically sound, perfect for preparing for or following up on a hormone test.
Why this approach makes sense
Adon Health combines evidence-based diagnostics with telemedicine care and subsequent therapy, sparing many men the hassle of navigating doctor's offices and enabling clear, safe, and efficient care. The platform has received numerous awards for its quality and collaborates with ISO-certified laboratories and German physicians.
Conclusion
Testosterone is more than just a hormone; it's a key regulator of body composition, mood, energy, libido, and performance. Diagnosis requires more than just a single blood test: SHBG, free and bound hormones, as well as TSH and lipid levels (including triglycerides) provide a comprehensive picture. Only then can individual causes be identified and appropriate therapies initiated , ranging from lifestyle optimization and nutritional supplements to medically supervised testosterone replacement therapy.
