George · The Biohack Diaries
Testosterone Therapy
Testosterone replacement therapy (TRT) is an important treatment for men with clinically low testosterone. It helps restore energy, libido, muscle mass, mood and cognitive function. Research shows that TRT not only improves physical strength and mental clarity but may also reduce visceral fat, improve sleep quality and even lower the risk of heart disease.
At the clinic, testosterone therapy is given as a long-acting testosterone injection (Nebido), supervised by your doctor from the first blood test onward. For men who truly need it, TRT isn't just about feeling younger. It's about reclaiming overall health, confidence and quality of life.
What it is and how it works
Nebido is testosterone undecanoate, a slow-release testosterone injection given deep into a muscle (usually the buttock) by a healthcare professional. After the injection, the testosterone is absorbed slowly over many weeks. This keeps hormone levels steady and long-lasting without the need for any daily treatment.
After an initial loading phase, Nebido is injected every 10–14 weeks, which means about four injections a year once your levels are stable.
Benefits of Nebido
Very convenient: no daily routine or messy application
No risk of skin-to-skin transfer to other people
Stable levels after the first few doses, with fewer fluctuations in testosterone
Only about four injections per year after stabilization, so fewer clinic visits
Things to consider
Each injection is given at the clinic
It may cause mild discomfort at the injection site
It cannot easily be stopped or adjusted once it has been injected
It takes a few weeks to reach full effect after the first dose
What it is for
Testosterone therapy is for men with low testosterone. It supports:
Energy
Libido
Mood
Muscle
Who it is for
TRT is recommended when a man has both low testosterone on blood tests and symptoms of low testosterone.
1. Low testosterone levels
Total testosterone below 300 ng/dL on two separate morning blood tests, or
Low free testosterone, especially if SHBG is abnormal or symptoms are strong
2. Clinical symptoms
At least one of the following:
Low sex drive or erectile dysfunction
Fatigue or low energy
Loss of muscle mass or strength
Depressed mood or irritability
Poor concentration or memory (brain fog)
Loss of body hair or increased body fat
Decreased bone density (osteoporosis or fractures)
Low testosterone self-check questionnaire
Doctors use clinical screening tools such as the ADAM questionnaire (Androgen Deficiency in Aging Males). Answer YES or NO to each question:
Do you have a decrease in sex drive (libido)?
Do you have a lack of energy or persistent fatigue?
Have you noticed a decrease in strength or endurance?
Do you feel a decrease in enjoyment of life?
Are you sad or grumpy more often than before?
Have you noticed a recent decline in your ability to concentrate, or in your memory?
Have you noticed a decrease in muscle mass or increased body fat?
Do you have fewer or weaker erections, including morning erections?
Do you fall asleep easily after dinner or feel excessively sleepy in the evening?
Have you noticed a decrease in work performance or motivation?
Have you experienced infertility or difficulty having children?
Do you have osteoporosis or a history of low-trauma fractures?
Scoring: if you answered YES to question 1 or 7, or to three or more questions in total, you may have symptoms of low testosterone. A blood test is the next step.
Who should not have it
Testosterone replacement can offer powerful benefits, but it is not safe or suitable for everyone. In certain medical conditions TRT should be avoided because it may cause harm.
Absolute contraindications (TRT must not be used)
Prostate cancer (active or suspected): TRT can potentially stimulate the growth of prostate tissue, including cancer cells.
Male breast cancer: although rare, it can be worsened by testosterone.
Very high red blood cell count (hematocrit above 54%): TRT can increase the risk of blood clots, stroke or heart attack.
Severe untreated sleep apnea: TRT may worsen breathing problems during sleep if the condition is not managed.
Severe heart failure: TRT may cause fluid retention and worsen the condition.
Allergy to testosterone or its components: for example, the castor oil in Nebido.
Relative contraindications (use with caution or under specialist supervision)
Elevated PSA or an enlarged prostate (needs evaluation first)
Fertility concerns: TRT can suppress sperm production
History of heart attack or stroke: requires close monitoring
Blood clotting disorders or a history of DVT/PE
Uncontrolled diabetes or obesity: the underlying risk factors need to be addressed
The treatment
Each testosterone injection appointment takes about 30 minutes, including observation after the injection. Treatment is doctor-supervised from start to finish.
Step 1: Starting lab set
Before treatment starts, your doctor orders a starting set of blood tests:
CBC (complete blood count, including hematocrit and hemoglobin)
PSA (prostate-specific antigen)
Total testosterone
Free testosterone
Step 2: Understanding your results
Not all testosterone in the body works the same way, so your doctor looks at several numbers to get the full picture.
Total testosterone is the main number and is tested first. It measures all the testosterone in your blood, both the active and inactive forms. The normal range is 300–1000 ng/dL. If your level is below 300 ng/dL on two separate mornings (7–10 am) and you have symptoms, treatment may be recommended.
Free testosterone is the active form that your body can actually use. Sometimes total testosterone looks fine but free testosterone is still too low, especially if your body makes too much of a protein called SHBG. The normal range is around 5–15 ng/dL (it varies slightly between labs). If your free testosterone is low, treatment may still be appropriate even with a normal total testosterone.
SHBG (sex hormone-binding globulin) is a protein in the blood that binds testosterone and makes it inactive. If SHBG is too high, it "locks up" too much testosterone and leaves you with less free testosterone. SHBG is tested when total testosterone is borderline or does not match your symptoms.
A simple analogy: think of total testosterone as all the money in your bank account, and free testosterone as the cash in your wallet. SHBG is the bank's security lock. It keeps the money safe, but you can't spend it. If the lock is too tight (high SHBG), you may have plenty in the bank but not enough to use.
When total testosterone is normal but symptoms exist
Check free testosterone. In many men, especially older men or those with high SHBG, total testosterone looks normal but free testosterone is low. Your doctor can order free testosterone and SHBG tests to assess how much hormone is actually available.
Check SHBG. High SHBG is common with aging, thyroid disease, liver disease and certain medications, and it lowers free testosterone.
Evaluate other causes. Fatigue, low libido and mood changes can also come from depression or anxiety, thyroid dysfunction, chronic illness, sleep disorders, or nutritional deficiencies such as low vitamin D or B12.
Step 3: The injection
Nebido is injected deep into a muscle, usually the buttock, by a healthcare professional. You then stay for a short period of observation before you go home.
Dosing schedule
Initial phase: two injections, 6 weeks apart
Maintenance phase: one injection every 10–14 weeks, depending on your response and lab results
How often: every 10, 12 or 14 weeks?
The ideal interval differs from person to person and depends on both your symptoms and your blood test results.
Standard maintenance: one injection every 10 to 14 weeks.
If symptoms return early (for example low energy, poor sleep, low libido or irritability), the injection may be needed sooner, such as every 10–12 weeks.
If you feel stable and symptom-free for the full period, the interval may be extended to 14 weeks.
Lab tests help decide:
Testosterone level (measured before your next injection): if it is still within the target range, the current schedule is fine. If it is too low, the interval is shortened.
Hematocrit: if it is higher than 54%, injections may need to be spaced further apart or the dose adjusted.
The goals of treatment are to maintain stable testosterone levels, keep symptoms under control and prevent side effects such as high hematocrit or hormone crashes. Your doctor sets and adjusts your schedule after an in-person assessment, and testosterone therapy can be combined with other treatments on the same day if your doctor advises it.
Before and aftercare
Common side effects and what to do
Injection site discomfort or swelling: mild soreness for 1–3 days is normal. Apply a warm compress or massage the area gently. Tell us if there is redness, severe pain or swelling.
Mood changes (irritability or emotional shifts): some men feel emotionally sensitive during hormonal peaks. Keep track of this and share it with your doctor, as the interval between injections may need adjusting.
Increased red blood cell count (high hematocrit): this may cause headaches, flushing or fatigue. It is checked regularly in your blood tests, and if levels are too high your dose or injection frequency may be adjusted.
Mild fluid retention or weight gain: watch your salt intake and blood pressure, and report any swelling in your legs or feet to your doctor.
Delayed effect with the first dose: because Nebido is slow-acting, it may take a few weeks to feel the full results after the first injection. Your doctor may schedule the second injection earlier (at 6 weeks).
Other possible side effects your doctor watches for include acne and hair loss.
When to contact us
A painful or inflamed injection site
Trouble urinating or other prostate symptoms
Mood swings or unusual emotional changes
No improvement in symptoms after 3 months
Quality and safety
Regular monitoring is essential to make sure testosterone therapy is working well without causing side effects. Your doctor tracks your hormone levels, blood health and prostate safety throughout treatment.
Testosterone levels: to keep levels in the healthy, therapeutic range, not too low and not too high. Checked before starting treatment, 6–8 weeks after starting or changing the dose, then every 3–6 months once stable.
Hematocrit and hemoglobin: TRT can increase the red blood cell count, which may raise the risk of blood clots. Checked before starting, 3 months after starting, then every 6–12 months. If hematocrit is above 54%, therapy may need to be paused or adjusted.
PSA (prostate-specific antigen): to monitor for prostate growth or signs of prostate cancer. Checked before starting (baseline), 3–6 months after starting, then once a year.
Symptoms and side effects: to track improvements in energy, libido and mood, and to watch for side effects such as acne, hair loss or mood swings. Reviewed at every visit.
The science
Does testosterone therapy cause cancer?
The short answer, based on current scientific evidence, is that there is no strong evidence that TRT causes prostate cancer or increases overall cancer risk in men.
Prostate cancer
In the past, it was believed that testosterone "feeds" prostate cancer. This idea came from early studies in the 1940s showing that prostate cancer slowed down when testosterone was removed. Modern research paints a more nuanced picture:
A large review published in European Urology (2016) found no increased risk of prostate cancer in men undergoing TRT.
The Testosterone Trials (TTrials) and studies published in JAMA (2017) also found no rise in aggressive prostate cancer in men treated with testosterone.
Interestingly, most prostate cancers occur in older men with low testosterone, not high testosterone.
Other cancers
There is no clear evidence linking TRT to cancers such as colon, lung or breast cancer in men. As a precaution, however, TRT is absolutely contraindicated in men with active prostate or breast cancer.
Why the concern?
Testosterone can make prostate tissue grow, so it can enlarge the prostate (benign prostatic hyperplasia, BPH). This causes urinary symptoms, but it is not cancer. That is why PSA is monitored regularly during therapy.
The bottom line: TRT does not cause prostate cancer, but we screen and monitor carefully to keep you safe. Many men with low testosterone feel better, become stronger and enjoy a better quality of life with proper, monitored treatment.
Frequently asked questions
How long does each appointment take?
About 30 minutes, including a period of observation after the injection.
Which blood tests do I need before starting?
The starting lab set is a CBC, PSA, total testosterone and free testosterone. Your doctor may also check SHBG if your total testosterone is borderline or does not match your symptoms.
How often will I need an injection?
Two injections 6 weeks apart to start, then one injection every 10–14 weeks, which is about four times a year. Your doctor adjusts the interval based on your symptoms and blood tests.
When will I feel the effect?
Nebido is slow-acting, so it may take a few weeks after the first injection to feel the full results.
Will testosterone therapy affect my fertility?
It can. TRT can suppress sperm production, so fertility concerns should be discussed with your doctor before you start.
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