Testosterone is the main male hormone. After the teenage years, more than 95% of the testosterone in your blood is made in your testicles. A small extra amount comes from “building blocks” made by your adrenal glands, such as DHEA, but these are very weak.¹

Testosterone works by attaching to a receptor inside your cells. The receptor then moves to your genes and switches them on.¹ This is why testosterone affects much more than your sex drive. It also acts on your muscles, bones, blood, mood and metabolism.

Can DHEA replace testosterone? No. DHEA supplements do not raise testosterone enough in men, but they do raise estrogen.¹ A man who truly lacks testosterone needs testosterone itself.

• Your brain is in charge. A part of the brain called the hypothalamus signals the pituitary gland, which releases a hormone called LH. LH tells your testicles to make testosterone. A second hormone, FSH, controls sperm production.¹
• A built-in thermostat. When testosterone is high enough, it tells the brain to slow these signals down.¹
• Treatment uses the same thermostat. Testosterone given as treatment also tells the brain to slow down. While you are on treatment, your testicles make much less testosterone and much less sperm of their own.²
• This is why treatment must be steady. Once your own production is turned down, almost all of your testosterone comes from your treatment. If you miss doses, or come late for an injection, your body does not make up the difference, so your symptoms can come back. The product information for the injection says it clearly: if you miss your injection appointments, your optimal testosterone level will not be maintained.³
• Talk to us before you stop. After stopping, your body needs time to start making its own testosterone again. Sperm production, for example, takes months to come back.² Treatment is an ongoing plan, so please keep your appointments, check your level with your doctor, and do not stop or delay on your own.

• Highest in the morning. Testosterone is highest in the morning and lowest in the afternoon.¹ In men aged 30 to 40, a test at 4 p.m. read 20–25% lower than a test at 8 a.m.²
• Food lowers it. Sugar lowers testosterone within 30 minutes, and a test after a meal can read more than 30% too low.⁴
• Not when you are ill. Testosterone falls for a while during an illness and while you recover, so we wait until you are well.⁵

In your blood, most testosterone is attached to carrier proteins. One of them, SHBG (sex hormone-binding globulin), holds it tightly. Only about 2% floats freely.⁶ This free part is the part that can enter your cells and do its work.

Why your total can look fine while your free testosterone is low. Your total testosterone is everything added together: the part held by SHBG, the part held loosely by another protein called albumin, and the free part. When SHBG is high, more testosterone is locked up. Your total then looks normal or even high, but the free part that actually works is low.⁵ SHBG rises with age, so in older men free testosterone falls more than total testosterone.⁷ The opposite also happens: being overweight or having diabetes lowers SHBG, so the total can look low while the free part is enough.^5,7

This is why we use your free testosterone, together with your symptoms, to decide on treatment. Guidelines recommend that free testosterone is measured with a reference method or calculated from total testosterone, SHBG and albumin.⁵ Our laboratory calculates it from these three results.

• A slow fall, not a sudden drop. From middle age, testosterone can fall by up to about 1% a year, and faster in men with long-term illness.¹ A large European study of ageing men (EMAS) found that total testosterone fell by 0.4% a year and free testosterone by 1.3% a year.⁴
• How common is a low level? About 30% of men over 60 and about 50% of men over 70 have a total testosterone level below the lower limit for young men.⁷
• Weight and health matter more than age. Being overweight and having long-term illnesses are linked with low testosterone more strongly than age itself.⁷ These include type 2 diabetes, metabolic syndrome, heart disease, long-term lung disease, kidney disease and cancer.⁴

How total and free testosterone change with age. Age 40 is set at 100%. The lines are calculated from the average yearly fall in the EMAS study; they show the average for a population, not any one man.⁴

We ask you to have your blood tests at our partner laboratory, even if you already have results from somewhere else. This is not for our benefit. Hormone results are not as simple as one number.

• Units differ. Laboratories report testosterone in different units, so the same level can look completely different on two reports.
• Normal ranges differ. The normal range for testosterone depends on the test kit, the reference standard and the group of people used to set the range.⁵
• Free testosterone has no shared range. Laboratories measure or calculate it in different ways, and there is still no single agreed normal range.⁵

Our treatment rules are built on the units and methods of our own laboratory, so numbers from another laboratory could lead to the wrong decision. If you bring results from elsewhere, we are happy to look at them as part of your history, and we recheck at our laboratory before starting or changing anything.

• Getting older, as described above.
• Being overweight, especially around the waist. A guideline advises checking testosterone in men with a body mass index (BMI) of 30 or more, or a waist over 40 inches.²
• Type 2 diabetes or metabolic syndrome.⁴
• Strong painkillers (opioids) or steroid tablets.⁴
• Using, or having recently stopped, anabolic steroids (muscle-building steroids). These switch off your own production. We do not treat this situation ourselves; we refer you to a hormone specialist (endocrinologist) at a hospital.⁴
• Alcohol, smoking, cannabis, beta-blockers (a medicine for blood pressure or the heart), tight underwear, swollen veins in the scrotum (varicocele), severe stress, very hard training or long-distance running. Physicians who focus on optimal hormone levels see lower testosterone in these situations.
• Anaemia without a known cause, thin bones, difficulty fathering a child, or a pituitary gland problem.^2,5

We sometimes see young men who train a lot and have a low testosterone result but no symptoms.

• Hard training can lower testosterone. European guidelines list endurance exercise as one cause of low testosterone that starts in the brain’s signals.⁴
• The test itself may be the reason. Hard exercise in the 1 to 2 days before the test, a late or non-fasting test, an illness or biotin supplements can all give a falsely low result.
• We will ask you directly about anabolic steroids. A large analysis found that 18.4% of people who did sport for fun and 13.4% of athletes had used anabolic steroids, compared with 1.0% of people who did no sport.¹ Stopping them is a known cause of low testosterone.⁵
• No symptoms means no treatment. Guidelines do not recommend testing or treating men who have no symptoms, no signs and no related illness, because we do not know that treatment helps them.^5,2 Instead, we repeat your test under the right conditions and check your brain’s signals. If it is still low, we look for the cause.

Medical guidelines describe signs that are more typical of low testosterone:⁴

• Sex life: lower sex drive, weaker erections, and fewer morning or spontaneous erections
• Body: finding hard activity, walking more than a kilometre or bending down more difficult; less energy; hot flushes
• Mood and mind: feeling low, less motivation, tiredness, poorer concentration and memory, poor sleep

The sexual signs are the most specific. In a large European study, they were the only ones that clustered with a low level.⁵

Physicians who focus on optimal hormone levels describe a wider range of milder signs. They are often present all day and worse with effort, because muscle is one of the main targets of testosterone:

• Body: looking older, belly fat, smaller and weaker muscles, aching muscles and joints, constant tiredness, poor sleep, sweating on the head and upper chest
• Sex and urine: lower sex drive, erections that are less frequent, less firm or shorter, less semen, getting up at night to pass urine
• Mind: irritability, anxiety, low self-confidence, difficulty making decisions, low mood, poorer concentration and memory

None of these signs is specific to low testosterone; all of them can have other causes.⁴ Only a blood test, read together with your symptoms, tells you whether testosterone is part of the picture.

Why we ask about symptoms at every visit. You fill in a short symptom checklist before you start and at every follow-up. A blood test alone cannot tell us whether you feel better, and how you feel alone cannot tell us whether your level is safe. We need both. Your answers show whether treatment is really helping you, and your blood tests keep the dose safe.²

We don’t ask you to take our word for it. This is what research has found in men with low testosterone:

• Sex life. In a clinical trial of men aged 65 and over with low testosterone (the TTrials), one year of treatment moderately improved sexual activity, sex drive and erections.⁵ The effect was clearest in men whose erection problems were mild. If erections are still not good enough, testosterone together with an erection medicine worked better than the erection medicine alone.⁴
• Bones. After 24 months, bone density in the spine and hip was about 3–4% higher than with a dummy treatment (placebo).²
• Blood. In men who had anaemia (too few red blood cells) at the start, 58% were no longer anaemic at the end of the study, compared with 22% on placebo.²
• Muscle and fat. Muscle increased by an average of 1.9 kg, and body fat fell by 1.6–1.8 kg.²
• Mood. In men with long-lasting mild depression (dysthymia), 53% recovered, compared with 19% on placebo.² Testosterone can support, but does not replace, treatment for more serious depression.⁴
• Blood sugar. In a two-year trial of 1,007 men whose blood sugar was starting to rise or who had newly diagnosed diabetes, fewer men went on to develop diabetes.⁴
• Urinary symptoms (early research). In a study that followed men for 8 years, scores for urinary symptoms improved on treatment.⁴
• Quality of life. Analyses that pooled many trials found a small improvement.⁴
• Heart safety. In the TRAVERSE trial of 5,198 men aged 45 to 80 with low testosterone who had heart disease or a high risk of it, serious heart and blood vessel events (heart attack, stroke or death from heart disease) happened in 7.0% of men using testosterone gel and 7.3% of men on placebo, so treatment did not increase them. The same trial found slightly more irregular heartbeat (atrial fibrillation: 3.5% vs 2.4%), sudden kidney injury (2.3% vs 1.5%) and blood clots in the lungs (0.9% vs 0.5%) in men using testosterone, which is one reason we check your health carefully before and during treatment.⁶

Physicians who focus on optimal hormone levels find that many men feel better within 1 to 3 months, while sexual function often takes 3 to 6 months to improve.

Where research has not shown a benefit Clinical trials so far have not shown that testosterone helps with:

• preventing broken bones. Bone density goes up, but there is not yet enough data on fractures, and one large trial saw slightly more fractures in men using testosterone (3.5% vs 2.5%);^4,6
• walking distance in older men;⁴
• controlling blood sugar in men who already have diabetes;⁴
• thinking and memory.⁴

We aim for the level of a healthy young man. Not lower, and not higher.

• Why not lower. Waiting with a low level and ongoing symptoms is not what we want for you. If you have symptoms and your level is below our optimal range, your doctor talks with you about treatment.
• Why not higher. More is not better. Too much testosterone can cause thick blood, acne and oily skin, breast swelling and hair loss,⁵ as well as irritability or restlessness.⁸ So we also set an upper safety limit, and your doctor lowers your treatment if your blood tests show signs of too much.

From Dr. Chontirot: natural levels, for natural results Testosterone has been used for a long time to go beyond what the body makes on its own. We are not here to judge that choice. Our approach is different: we aim for natural levels, for natural results. In clinical trials, treated men gained on average 1.9 kg of muscle and lost 1.6–1.8 kg of fat.² These are real changes, but they are not the fast, oversized muscle growth some people are looking for. If you want results beyond what is natural, you would need levels beyond what is natural, and you would also accept the side effects that come with them. Balance is the key.

Your first test is part of your Annual Panel. For testosterone we look at:

• Free Testosterone. One test that gives us four results together: total testosterone, SHBG, albumin and free testosterone, calculated from the other three.
• LH and FSH, the brain’s signals to the testicles. They show whether a low level starts in the testicles or in the brain.⁵
• Prolactin, to check the pituitary gland.⁵
• Estradiol, a form of estrogen. Your body makes it from testosterone, so we keep a starting value to compare with later.¹
• A full blood count, because testosterone makes more red blood cells and can thicken the blood.⁴
• PSA, a prostate blood test.⁵
• Blood fats and HbA1c (a measure of blood sugar), as a starting point for your metabolism.⁴

On test day:

• Come between 7 and 10 a.m., before breakfast. Testosterone is highest in the morning and food lowers it.⁴
• Stop biotin for at least 3 days before every blood test. Biotin, found in hair, skin and nail supplements, interferes with the LH and FSH tests.⁵
• Avoid hard exercise for 2 days before the test. Hard activity in the 1 to 2 days before a blood test can lower your result.
• Drink plenty of water the day before and on the morning of the test. Coming in dehydrated can change your blood results.

Testosterone at the right level is safe for most men, but it is not one size fits all. When a doctor looks after you, most risks can be prevented by checking before you start and following up on time. Buying it yourself skips these steps.

• Some men need special consideration first. For example, men with a high blood count, a high prostate test (PSA), or a pituitary gland problem. These are found through your history and your blood tests, not from the outside. Not everyone can use the same product or the same dose, so our doctor checks your history first. If you need closer care than we can give, we work with the doctor who already looks after you.
• The dose must match your blood tests. Too little does not help; too much can thicken the blood or swell the breasts. Very high doses have more serious side effects,² and the product information warns that misusing testosterone or anabolic steroids can harm the heart, liver and mind, and can lead to dependence.⁹
• It lowers sperm production. If you would like children, you need to know this before you start.²
• The gel can pass to people at home. You need to learn how to protect your partner and children.⁶
• Stopping on your own brings symptoms back, because your own production is turned down during treatment.

Products bought elsewhere vary in quality and strength, so neither you nor a doctor can tell what level they give you. With us, every dose is matched to your blood tests.

• Symptoms and a low result, together. We start treatment when you have symptoms of low testosterone and your morning blood test is low. A low result alone, without symptoms, is not a reason to start.⁵ The exception is anaemia without a known cause or thin bones, which count as signs of low testosterone.^5,2
• Fixing the causes alongside treatment. If being overweight, a medicine or another illness is lowering your testosterone, we work on it at the same time. Losing weight and exercising raise testosterone only a little,⁴ so we do not make you wait until these are fixed.
• Two forms; you choose. We use body-identical testosterone (the same hormone your body makes) as a daily gel or a long-acting injection. Both are approved for low testosterone in men.^8,10 The gel is the choice for you if your blood count is on the high side, or if you take an anticoagulant blood thinner such as warfarin, apixaban, dabigatran, edoxaban or rivaroxaban. Aspirin or clopidogrel alone does not rule out the injection.

Testosterone gel

• How it is used: You rub it on your skin once a day, in the morning.
• May suit you if: you are happy to use it every day and would like a treatment that can be stopped quickly.
• Things to know: It can pass to other people through skin contact. About 1 in 10 men get red, irritated or dry skin or spots where they apply it.⁸

Long-acting testosterone injection

• How it is used: Your doctor injects it deep into the buttock muscle at our clinic, every few months.
• May suit you if: you prefer not to use something every day and can come for your injection appointments.
• Things to know: It raises the blood count more than the gel. It can cause soreness where it is injected, and rarely a brief cough or breathlessness.^2,10

• Gel: your doctor sets your dose and adjusts it by your blood tests and how you feel.
• Injection: your doctor sets the time between injections and adjusts it by your blood tests and by whether your symptoms come back before your next injection is due.
• If it is not helping. Some benefits take months to appear. If, after a fair trial with your level where it should be, your symptoms have not truly improved, your doctor will talk with you about stopping.² This does not apply if you are treated for thin bones or anaemia.

• Gel: a blood test and consultation at 3, 6 and 12 months after you start, then once a year. Your level is steady from the second day of daily use,⁸ and many men feel better within the first few months, so a visit at 3 months lets your doctor look at your blood test and your symptoms together.
• Injection: we take your blood on the morning of your injection, before you are injected, at about 3, 6 and 12 months, then once a year. You do not need extra visits.
• Why the blood count and PSA. The blood count usually rises in the first 3 to 12 months, and European guidelines advise checking testosterone and the blood count at 3, 6 and 12 months, then yearly.⁴ We check PSA at the same visits so you only come once.
• Every blood test comes with a consultation. Your doctor goes through your result, your symptoms and your checklist with you each time.

1. Handelsman DJ. Androgen Physiology, Pharmacology, Use and Misuse. In: Feingold KR, et al., editors. Endotext. South Dartmouth (MA): MDText.com; updated 2020.

2. Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. American Urological Association; 2018.

3. Package leaflet: testosterone undecanoate 1000 mg/4 mL solution for injection (United Kingdom). Revised December 2025.

4. Salonia A, Boeri L, Capogrosso P, et al. EAU Guidelines on Sexual and Reproductive Health. European Association of Urology; 2026.

5. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744. doi:10.1210/jc.2018-00229

6. Prescribing information: testosterone gel 1% for topical use (United States). Revised 10/2025.

7. Bhasin S, Valderrábano RJ, Gagliano-Jucá T. Age-Related Changes in the Male Reproductive System. In: Feingold KR, et al., editors. Endotext. South Dartmouth (MA): MDText.com; updated 2022.

8. Package insert (Thailand): testosterone gel 50 mg in 5 g sachet, summary of product characteristics.

9. Summary of product characteristics: testosterone undecanoate 1000 mg/4 mL solution for injection (United Kingdom). Revised 15 December 2025.

10. Package insert (Thailand): testosterone undecanoate 1000 mg/4 mL solution for injection. CCDS version 10, 27 September 2021.