Testosterone does a lot more than most people realise. While it is often spoken about in the context of sex drive or muscle mass, this hormone plays a central role in energy production, mood regulation, bone strength, cognitive function, and cardiovascular health. When levels fall below what the body needs, the effects ripple across nearly every system.
Low testosterone, sometimes called low T or hypogonadism, is more common than many expect. Research suggests that around 2 in 100 men have clinically low testosterone levels, though rates increase significantly with age. Some estimates suggest that up to 40% of men over 45 may experience symptoms consistent with testosterone deficiency.
If you have been feeling off in ways that are hard to explain, such as persistent fatigue, low mood, changes in body composition, or a reduced interest in sex, testosterone may be worth looking at. This guide walks through the full range of symptoms, what causes them, and what you can do about it.
This article is for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. If you are concerned about your hormone levels, please speak with a qualified healthcare provider.
What Is Testosterone and What Does It Do?
Testosterone is a steroid hormone produced primarily in the testes in men, with smaller amounts made in the adrenal glands. In women, the ovaries and adrenal glands produce testosterone in much smaller quantities, though it still plays an important role in health.
In men, testosterone is responsible for:
- Development of sexual characteristics during puberty
- Regulation of sex drive and reproductive function
- Maintenance of muscle mass and physical strength
- Bone density and skeletal health
- Red blood cell production
- Mood, cognitive function, and general sense of wellbeing
- Fat distribution and metabolic rate
Testosterone levels are at their peak during early adulthood and begin a gradual natural decline from around age 30 onward, typically dropping by about 1 to 2 percent per year. While this is a normal part of ageing, some men experience a more significant decline that leads to noticeable symptoms.
Common Symptoms of Low Testosterone
One of the reasons low testosterone often goes undiagnosed is that its symptoms are wide-ranging and can easily be attributed to stress, poor sleep, or just getting older. But when multiple symptoms appear together, they paint a clearer picture.
1. Fatigue and Low Energy
This is one of the most frequently reported symptoms. People with low testosterone often describe a bone-deep tiredness that rest does not fully relieve. It is not the same as feeling sleepy. It is a persistent flatness, a sense of running on empty even after a full night of sleep.
Testosterone supports mitochondrial function and red blood cell production, both of which are central to how efficiently your body produces and uses energy. When those processes are compromised, fatigue can become chronic.
2. Reduced Sex Drive (Low Libido)
Testosterone is the primary driver of sexual desire in men. A noticeable and sustained drop in interest in sex, particularly when it represents a clear change from your normal baseline, is one of the most telling signs of low T.
It is worth distinguishing this from the natural fluctuation in desire that happens with stress or relationship factors. Low testosterone tends to produce a more consistent, prolonged reduction that does not resolve when circumstances improve.
3. Erectile Dysfunction
While erectile dysfunction has multiple causes including cardiovascular disease, diabetes, and psychological factors, low testosterone can contribute. Testosterone helps trigger the release of nitric oxide in the body, which plays a role in the physical process that enables erections.
Low T is less commonly the sole cause of erectile dysfunction but often works alongside other contributing factors. If you are experiencing ED alongside other symptoms on this list, it is worth including hormone testing as part of any investigation.
4. Mood Changes and Depression
Testosterone has a direct influence on brain chemistry, including the regulation of serotonin and dopamine. Men with low testosterone frequently report symptoms of depression, irritability, difficulty concentrating, and a general loss of motivation or pleasure in activities they previously enjoyed.
Research has found a consistent association between low testosterone and depressive symptoms, though the relationship is bidirectional: depression can also suppress testosterone production. This can make it difficult to untangle, which is another reason testing is helpful.
5. Difficulty Concentrating and Brain Fog
Many men with low T describe a sense of mental cloudiness. They may find it harder to focus, to retain information, or to think clearly. Word retrieval can feel slower. Tasks that were once straightforward may require more effort.
Testosterone receptors are present throughout the brain, particularly in areas related to memory and cognition. When levels fall, these cognitive functions can be affected.
6. Loss of Muscle Mass
Testosterone is an anabolic hormone, meaning it supports the building and maintenance of muscle tissue. Low levels make it harder for the body to build muscle even with regular exercise, and easier to lose it. You may notice that your strength has declined or that workouts feel less productive than they used to.
7. Increased Body Fat
Testosterone influences how the body distributes and stores fat. Men with low testosterone often accumulate more visceral fat, the kind stored around the abdomen and internal organs. This is not just an aesthetic concern. Visceral fat is metabolically active and associated with increased risk of cardiovascular disease and insulin resistance.
There is also a feedback loop to be aware of: excess body fat can lower testosterone levels further, because fat tissue contains an enzyme called aromatase that converts testosterone into oestrogen.
8. Bone Density Loss
Testosterone plays an important role in maintaining bone mineral density. Men with chronically low testosterone are at higher risk of osteoporosis and bone fractures, particularly as they age. This symptom is often silent until a fracture occurs, which is why it is important not to wait for obvious signs before investigating hormone health.
9. Sleep Disturbances
Low testosterone is associated with disrupted sleep, including difficulty falling asleep, staying asleep, or feeling unrefreshed despite adequate hours in bed. There is also a relationship between low T and sleep apnoea, a condition that itself suppresses testosterone production, creating another potential feedback loop.
10. Reduced Body Hair and Changes in Skin
Testosterone supports the growth of body and facial hair. Noticeable thinning of body hair, including chest, underarm, and pubic hair, can be a sign of declining hormone levels. Some men also notice changes in skin texture or reduced skin thickness.
11. Smaller Testicle Size
In some cases, particularly with primary hypogonadism (where the testes themselves are producing less testosterone), men may notice a reduction in the size of the testicles. This is a less commonly discussed symptom but worth including for completeness.
12. Hot Flushes
Often thought of as a symptom exclusively associated with menopause, hot flushes can also occur in men with low testosterone. They may present as sudden feelings of warmth, sweating, or flushing, particularly in the upper body and face.
13. Anaemia
Testosterone stimulates the production of red blood cells. Low levels can lead to mild anaemia, which may contribute to feelings of fatigue, weakness, and dizziness.
What Causes Low Testosterone?
Low testosterone is not always the result of ageing alone. There are two main categories of causes:
Primary Hypogonadism
This occurs when the testes themselves are not producing enough testosterone. Causes include:
- Klinefelter syndrome (a chromosomal condition)
- Undescended testicles
- Injury or infection affecting the testes
- Cancer treatments including chemotherapy or radiation to the pelvic area
- Mumps orchitis (inflammation of the testicles following mumps infection)
Secondary Hypogonadism
This occurs when the problem originates in the brain, specifically in the hypothalamus or pituitary gland, which regulate testosterone production through hormonal signals. Causes include:
- Pituitary disorders or tumours
- Kallmann syndrome
- Obesity
- Type 2 diabetes
- Obstructive sleep apnoea
- Chronic stress
- Excessive alcohol consumption
- Opioid or corticosteroid medications
- Inflammatory conditions such as HIV, sarcoidosis, or tuberculosis
Lifestyle and Environmental Factors
Even in the absence of a diagnosable condition, certain lifestyle factors can suppress testosterone production:
- Chronic sleep deprivation
- Sedentary behaviour
- A highly processed, nutrient-poor diet
- High levels of chronic psychological stress
- Exposure to endocrine-disrupting chemicals (found in some plastics, pesticides, and personal care products)
- Very low body fat or extreme caloric restriction
How Is Low Testosterone Diagnosed?
Diagnosis begins with a blood test. Because testosterone levels fluctuate throughout the day, with levels typically highest in the morning, the standard recommendation is to have blood drawn between 7am and 10am.
A single low reading is usually not sufficient for diagnosis. Most guidelines recommend confirming low levels with at least one or two additional tests on separate days, combined with a clinical assessment of symptoms.
Normal testosterone levels in adult men are generally considered to fall between 300 and 1000 ng/dL (nanograms per decilitre), though reference ranges can vary slightly between laboratories and testing methods. A result below 300 ng/dL is typically considered low, though symptoms and clinical context matter as much as the number.
Your doctor may also test for:
- Luteinising hormone (LH) and follicle-stimulating hormone (FSH), which help identify whether the problem originates in the testes or the pituitary gland
- Sex hormone-binding globulin (SHBG), which affects how much testosterone is biologically available
- Prolactin levels
- Thyroid function
- Full blood count and metabolic panel
Treatment Options
Treatment depends on the cause, the severity of symptoms, and individual health factors. Always discuss options thoroughly with a qualified healthcare provider before beginning any treatment.
Testosterone Replacement Therapy (TRT)
TRT is the most commonly prescribed medical treatment for low testosterone. It is available in several forms:
- Topical gels or creams applied daily to the skin
- Injections, either self-administered or given in a clinic, typically every one to three weeks
- Transdermal patches worn on the skin
- Subcutaneous pellets implanted under the skin every three to six months
- Oral testosterone tablets or buccal systems (less commonly used)
TRT can be highly effective at relieving symptoms, but it is not without considerations. It can affect fertility by suppressing the body’s own sperm production, so men who wish to have children in the future need to discuss this carefully with their doctor. Regular monitoring of haematocrit (red blood cell volume), prostate health, and hormone levels is standard practice during treatment.
Lifestyle Interventions
For men with borderline or mildly low testosterone, and often alongside medical treatment, lifestyle changes can make a meaningful difference:
- Regular resistance exercise and high-intensity interval training have been shown to support testosterone levels
- Prioritising sleep quality and duration
- Achieving and maintaining a healthy body weight
- Reducing alcohol intake
- Managing chronic stress through evidence-based practices such as mindfulness, therapy, or structured relaxation
- Eating a nutrient-dense diet with adequate protein, healthy fats, and zinc and vitamin D-rich foods
Addressing Underlying Causes
If low testosterone is the result of another condition, such as a pituitary tumour, sleep apnoea, or type 2 diabetes, treating that underlying condition is a central part of management and can result in significant improvement in testosterone levels.
When to See a Doctor
It is worth making an appointment with your doctor if you are experiencing several of the symptoms described in this article, particularly if they have developed gradually over time and represent a change from your normal baseline.
There is no need to wait until symptoms are severe. Early investigation and, if needed, early intervention typically leads to better outcomes. Bring a list of your symptoms, including when they started and how they affect your daily life. This kind of detail makes it much easier for your doctor to assess what is happening.
If you are experiencing symptoms of depression or are struggling with your mental health, please reach out to a healthcare professional directly. Mental health symptoms associated with low testosterone should be assessed and supported regardless of whether hormone levels are the primary cause.
Frequently Asked Questions
Can women have low testosterone?
Yes. Women produce testosterone in smaller amounts, but it still plays a role in energy, libido, mood, and bone health. Low testosterone in women can present with similar symptoms to those described above. This is a less well-studied area, and diagnosis can be more complex given the natural variation across the menstrual cycle and through menopause.
Is low testosterone the same as andropause?
Andropause, sometimes called male menopause, is a colloquial term used to describe the constellation of symptoms some middle-aged and older men experience as testosterone declines with age. Unlike female menopause, which involves a relatively rapid hormonal shift, the testosterone decline in men is gradual. Not all men will experience significant symptoms, and not all men with symptoms will have levels that fall below clinical thresholds. The term andropause is not a formal medical diagnosis.
Can low testosterone be temporary?
Yes. In some cases, testosterone levels can be temporarily suppressed by acute illness, extreme physical stress, severe caloric restriction, or the use of certain medications. When the underlying cause resolves, testosterone may return to normal. This is one reason why doctors typically confirm low levels with more than one test before proceeding to treatment.
Does TRT increase the risk of prostate cancer?
This has been an area of active research and historical debate. Current evidence does not support the idea that TRT causes prostate cancer in men who do not already have it. However, because testosterone can stimulate the growth of existing prostate cancer, TRT is generally not recommended for men with active prostate cancer. Regular monitoring of prostate-specific antigen (PSA) levels is standard practice during treatment.
A Final Word
Living with unaddressed low testosterone can significantly affect quality of life. The good news is that it is an area where investigation and intervention can make a real, measurable difference.
If you recognise yourself in these symptoms, the most useful thing you can do is to take them seriously and bring them to a healthcare professional you trust. You do not have to accept feeling chronically tired, low in mood, or unlike yourself as an inevitable part of getting older. Some of it might be, but some of it might also be addressable.
Understanding your hormone health is part of understanding your overall health, and that is always worth pursuing.
Medical Disclaimer
This article is intended for general informational purposes only and does not constitute medical advice. The content is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of your physician or another qualified health professional with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read here.
Sources and Further Reading
American Urological Association: Evaluation and Management of Testosterone Deficiency
Endocrine Society Clinical Practice Guideline on Testosterone Therapy in Men with Hypogonadism
NHS: Male hypogonadism (nhs.uk)
Mayo Clinic: Male hypogonadism (mayoclinic.org)
