LOW TESTOSTERONE

Testosterone is a sex hormone. Everyone produces it, though men produce far more.

In men it's made mainly in the testes, controlled by the brain and the pituitary gland. The pituitary signals the testes to produce testosterone, and a feedback loop dials production back down when levels rise. The adrenal glands add a smaller amount in the form of DHEA and DHEA-S, which the body converts into stronger androgens.¹ Some testosterone is converted again into dihydrotestosterone (DHT), a more potent version, by an enzyme called 5-alpha-reductase.²

Production climbs until roughly age 30, then starts to fall. For some men that decline is where symptoms begin.

Testosterone drives male sexual development, both before birth and through puberty.³ It's needed for the testes to descend, for sperm production, and for the penis and testes to grow.

After puberty it maintains muscle mass, bone strength, body hair, and a deeper voice. It also stimulates red blood cell production, which is why men typically have higher counts than women.

As levels fall with age, some of that reverses: smaller testes, lower libido, thinner bones, less muscle, more fat, and sometimes anaemia.

Testosterone does more than drive libido. It affects bone, muscle, mood, and cognition.

For bone, testosterone converts into estradiol, which activates oestrogen receptors in bone and helps maintain density.⁴ There's also a well-established link between vitamin D levels and free testosterone, independent of age and body weight.⁵

For muscle, testosterone on its own does little. Combined with strength training, it produces measurable gains in older men.⁶

For the brain, testosterone has been linked to short-term improvements in memory.⁷ Its relationship with mood is less tidy. Low levels are associated with depression in some groups, and high levels have been linked to low mood and hypomania, which is one reason treatment is kept within clinical limits.⁸

Testosterone falls by roughly 1% a year from around age 30 to 40.⁹

Defining normal is harder than it sounds. Levels shift with thyroid function and protein status, and the same number can mean different things at different ages. Historically the diagnostic threshold didn't vary by age at all. That's now being questioned, with calls for age-specific reference ranges when assessing younger men.¹⁰

Which is why a number on its own doesn't give you an answer.

The British Society for Sexual Medicine treats total testosterone of 12 nmol/L or above as within the normal range for men.¹¹

That threshold isn't a hard line. Some men sitting above it, at 14 nmol/L say, still have symptoms, usually because their own baseline used to be higher and has since dropped. The number is technically normal. The change isn't.

So assessment always combines a blood test with a clinical consultation covering symptoms, history, and lifestyle.

Healthy testosterone supports red blood cell production, muscle mass, bone density, sexual function, and mood.¹²

Low levels are associated with higher cardiovascular risk, including coronary artery disease, metabolic syndrome, and type 2 diabetes.¹³ Treatment has improved some cardiac measures in men with existing disease, and insulin resistance in men with diabetes and prediabetes.¹⁴ The wider relationship between testosterone and heart health is still being worked out.

For body composition, treatment reduces fat mass and increases lean mass, most clearly alongside resistance training.¹⁵ It also increases bone density at the spine and hip.¹⁶

Untreated low testosterone affects more than libido. Recognised consequences include reduced sex drive, erectile dysfunction, low mood, fatigue, loss of muscle mass and strength, and osteoporosis with a raised fracture risk.¹⁷

Longer term, untreated hypogonadism has been linked to coronary artery disease, stroke, and higher all-cause mortality, particularly in older men.¹⁸,¹⁹ Low testosterone can also reduce red blood cell production, causing anaemia, and impair sperm production.

How much any of this affects you varies. Diagnosis and treatment early makes a difference.

Low testosterone doesn't automatically cause infertility. Sperm production depends mainly on other hormones. But testosterone inside the testicles sits at far higher concentrations than in the blood, so it does play a supporting role.

The indirect effects matter too. Lower libido and erectile difficulties can make conception harder simply through frequency.

Testosterone taken as treatment is a different matter. It suppresses the hormones that drive sperm production, and has been studied as a male contraceptive for exactly that reason.²⁰^,²¹ Most men recover normal sperm production after stopping, though it can take up to two years.

Low testosterone comes in two forms, depending on where the problem sits.²²

Primary hypogonadism starts in the testicles. Causes include genetic conditions such as Klinefelter syndrome, undescended testicles, injury, cancer treatment, and ageing. The testicles themselves can't produce enough.

Secondary hypogonadism starts in the brain. The hypothalamus and pituitary send the signals that tell the testes to produce testosterone. If that chain breaks, through Kallmann syndrome, inflammatory disease, HIV, some medications, or obesity, the testes are healthy but under-instructed.

Either can be present from birth or acquired later. The distinction matters because it changes what treatment makes sense.

The BSSM now separates testosterone deficiency, the syndrome, from hypogonadism, the specific disorder causing it.²³

Several conditions lower testosterone, and often the relationship runs both ways.

Type 2 diabetes is the most common. A large proportion of men with type 2 diabetes also have low testosterone, probably through insulin resistance.²⁴

Obesity raises the activity of aromatase, the enzyme that converts testosterone into oestrogen.²⁵ Non-alcoholic fatty liver disease works through a similar route.²⁶

Sleep apnoea cuts deep and REM sleep, which is when testosterone production peaks.²⁷ Kidney failure reduces luteinising hormone production.²⁸ Head injuries affecting the pituitary or hypothalamus can disrupt the signal entirely.²⁹

Testicular injury, HIV, iron overload, and genetic conditions including Kallmann and Klinefelter syndromes can all reduce production directly.

Estimates put it at 10% to 40% of men globally, though the range is that wide because countries use different diagnostic thresholds.³⁰ In the UK, around 9% of men are thought to be affected, roughly 1 in 11.

Some symptoms point fairly directly at low testosterone: reduced sex drive, weaker or fewer erections, loss of body hair, less beard growth, loss of muscle, persistent fatigue, weight gain, and low mood.³¹

Others are less specific: low energy, poor stamina, weaker memory, trouble finding words, difficulty concentrating, and underperforming at work.³² Any one of these on its own means little.

It's the combination that matters. Persistent tiredness alongside reduced desire and low mood is worth investigating.

Sometimes, though rarely on its own.

Erectile dysfunction (ED) means being unable to get or keep an erection.³³ It's common: around 4.3 million men in the UK are affected each year.³⁴,³⁵

Between 20% and 40% of men with ED have low free testosterone.³⁶ Both conditions become more common with age, so the two often appear together without one causing the other.

Where testosterone does contribute, it works on two levels: in the brain, releasing the neurotransmitters that initiate an erection, and at the spinal level, influencing the nerves controlling blood flow.³⁷

ED has many other causes, including medication, so it's worth getting properly assessed rather than assuming hormones.

Reduced libido is one of the more specific signs of low testosterone.

Desire is governed by neural circuits where testosterone and its derivatives bind to androgen receptors. As levels fall, those receptors are activated less, and libido tends to follow.³⁸

Hormones aren't the whole story. Depression, stress, anxiety, and relationship difficulties all affect desire independently.³⁹ Researchers still can't say precisely how low testosterone reduces sex drive, only that the association is consistent.

Yes. Testosterone binds to androgen receptors in muscle cells and helps maintain muscle fibre integrity. When levels drop, those receptors are activated less and fibres weaken over time.⁴⁰

Some loss is simply age. Muscle mass peaks in the late twenties and then falls by roughly 1% to 2% a year, with strength falling 2% to 3%.⁴¹

The TEAAM trial, one of the largest non-injectable testosterone studies, found long-term treatment produced modest gains in upper body strength, muscle power, and lean mass, with inconsistent results for lower body strength.⁴²

The two feed each other, which is what makes it stubborn.

Fat cells produce aromatase, the enzyme that converts testosterone into oestrogen. More fat means more conversion, which means less available testosterone.⁴³ Lower testosterone then reduces muscle mass, which slows metabolism, which makes further weight gain easier.

Abdominal fat is most closely linked, and it carries its own cardiovascular risk. The European Male Aging Study found obesity was associated with a significantly higher risk of secondary hypogonadism, and even men who were only overweight showed reduced levels.⁴⁴

Often, though fatigue has plenty of other causes.

As testosterone falls, body composition shifts towards more fat and less muscle, which makes exercise feel harder and motivation lower. Low testosterone also disrupts sleep, so mornings start rough. Each part makes the next worse.

Ageing, depression, and poor sleep all cause fatigue on their own, so tiredness alone isn't enough to point at hormones.

The symptoms overlap enough that one gets mistaken for the other. Irritability, anxiety, low mood, reduced libido, memory problems, poor concentration, and disturbed sleep appear in both.

The physical signs differ. Breast swelling and loss of muscle mass point to low testosterone. Headaches and back pain are more typical of depression.

Research hasn't found a consistent relationship between testosterone levels and depression, but lower levels are frequently associated with depressive symptoms.⁴⁵ Some men respond particularly well to treatment, including those with milder depression, severe testosterone deficiency, or using gels rather than injections.⁴⁶

If you're taking an antidepressant, keep taking it. Any change should be a decision you make with your prescriber.

Testosterone crosses the blood-brain barrier, so it acts on the brain directly. It's been shown to slow nerve cell death and support regrowth after damage.

Cognitive decline with age affects verbal and visual memory, executive function, and spatial ability, and it tracks alongside falling testosterone. Supplementation has improved learning and memory in clinical studies, with even six weeks of treatment improving spatial and verbal memory in older men.⁴⁷

The likely mechanism is better blood flow to the brain. PET imaging has shown improved visuospatial performance after treatment, probably through androgen receptors in the brain.⁴⁸,⁴⁹

See Q55 for what happens to memory on treatment, where the evidence is more mixed.

Testosterone rises during sleep and peaks during the first REM episode.⁵⁰ Sleep deprivation cuts production, and lower testosterone worsens sleep quality, so the problem compounds.

It gets harder from middle age, when deep sleep naturally shortens and awakenings become more frequent. Men in this group who sleep badly tend to see a steeper drop in testosterone.⁵¹

As testosterone falls, cortisol rises, which raises alertness at exactly the wrong time and shortens sleep further.⁵²

Get a blood test. A venous test, taken from the vein, is the most reliable way to measure testosterone.

It's worth choosing a test that also looks at the cause. Luteinising hormone and follicle-stimulating hormone indicate whether the problem sits in the testes or the brain. High levels suggest primary testicular failure. Low levels point to the pituitary or hypothalamus.

Sleep is worth attending to in the meantime. Aim for 7 to 9 hours.⁵³ Both too little and too much can reduce testosterone.⁵⁴

Don't sit on symptoms. They rarely resolve on their own.

It depends what's causing it.

Where low testosterone is driven by something reversible, obesity being the clearest example, treating that can restore levels on its own. Losing weight and improving fitness sometimes brings testosterone back into range.⁵⁵

Where the cause is hypogonadism itself, treatment is usually long term. Testosterone replacement therapy (TRT) improves body weight, metabolic markers, and quality of life, but stopping generally reverses those gains and symptoms return. Restarting usually brings them back.⁵⁶

Yes. It's called hypogonadism, and it's a recognised condition caused by reduced function of the testes or of the glands that signal them.⁵⁷

It's more common with age, obesity, and type 2 diabetes.⁵⁸,⁵⁹

Sometimes low testosterone is part of another condition, such as Kallmann or Klinefelter syndrome.⁶⁰,⁶¹ And sometimes the symptoms come from something else entirely, such as obesity or depression, rather than the hormone.⁶²

Whatever the cause, it presents similarly: reduced libido, erectile dysfunction, fatigue, less strength and endurance, and mood changes.⁶³ Erectile dysfunction is usually what prompts men to get checked.

Diagnosis needs symptoms and blood results together. Neither is enough alone.

It starts with symptoms that haven't resolved: reduced libido, erectile dysfunction, fatigue, less strength, mood changes. Obesity, type 2 diabetes, and cardiovascular disease all make low testosterone more likely.²³

Blood tests then confirm it and look for the cause: total testosterone, free testosterone, prolactin, luteinising hormone, follicle-stimulating hormone, and a full blood count.

Timing matters. Testosterone is highest in the morning and is affected by blood glucose, so the sample should be taken fasted, within a few hours of waking.⁶⁴ Non-fasted results can read up to 30% lower.⁶⁵

Two readings below 12 nmol/L on separate occasions support a diagnosis. A drop well below your own baseline, alongside symptoms, can also support one even if the number stays in range.

An endocrinologist, a urologist, or a doctor with a specialist interest in testosterone deficiency.⁶⁶,⁶⁷

Endocrinologists specialise in hormones. Urologists specialise in the male reproductive and urinary systems. Either can order the right tests, examine you, and work out the underlying cause.

A GP can order a testosterone test, but interpreting borderline results and managing treatment is specialist work. If your GP can't identify the cause or the treatment isn't working, ask for a referral.

Because a single reading can mislead.

Testosterone fluctuates through the day and responds to things like blood glucose, so one low result might be a bad morning rather than a pattern.⁶⁸

The first test sets your baseline. The second, ideally about two weeks later, confirms the level is consistently low rather than a one-off. Both should be taken in the morning, on an empty stomach.

A full assessment measures more than testosterone itself.⁶⁹

Total testosterone is everything in the blood, bound and unbound.⁷⁰ Free testosterone is the small unbound fraction that can actually act on tissue.

SHBG and albumin are the proteins testosterone binds to. SHBG binds tightly and controls how much is available, so high SHBG can leave you symptomatic with a normal total.⁷¹ Albumin binds more weakly.⁷²

Luteinising hormone and follicle-stimulating hormone show where the problem sits. Raised levels suggest the testes aren't responding. Low levels suggest the pituitary isn't signalling.⁷³

Prolactin, if high, suppresses testosterone and can cause erectile dysfunction and low libido even with normal levels.⁷⁴ ALT and AST check liver function, since the liver metabolises testosterone.⁷⁵

Total testosterone is everything in your bloodstream. Free testosterone is the small unbound fraction, around 2% to 5%, that can actually enter cells and do something.⁷³,⁷⁶

That's why you can have a normal total and still have symptoms. If most of it is bound to SHBG, very little is available.

Men produce small amounts of oestrogen, and it matters. It helps regulate libido, erectile function, and sperm production.⁷⁷

With age, testosterone falls while oestrogen stays roughly level.⁷⁸,⁷⁹ That shifting ratio can cause gynaecomastia, breast tissue enlargement, and contribute to erectile dysfunction.

Body fat drives this. Fat tissue raises aromatase activity, which converts testosterone into oestrogen, pushing the ratio further in the wrong direction.⁸⁰

Accuracy. A venous sample gives a larger volume and a cleaner result.

Finger-prick samples can read falsely high or low. Blood cells rupture during collection, interstitial fluid dilutes the sample when the finger is squeezed, and proteins can interfere.⁸¹

Finger-prick tests are more convenient and fine for plenty of purposes. For testosterone, where the result determines whether you're offered a prescription medicine, the venous test is the standard.⁸²

The Aging Males' Symptoms scale is a short questionnaire that scores 17 symptoms across psychological, physical, and sexual health, each rated 1 to 5.⁸³

It takes a few minutes and produces a composite score. Clinicians use it alongside blood results to judge symptom severity, and it can help separate hormonal from vascular causes of erectile dysfunction.

Come prepared with three things.

Your symptoms, and how long they've been going on. Be specific about what's changed and how it's affecting work and home life.

Your medical history and medications, current and past, plus any family history of low testosterone.⁶⁵

Your lifestyle. Diet, exercise, stress, and sleep quality all affect testosterone.⁸⁴

A physical examination may follow, checking for signs such as gynaecomastia or reduced testicular size, along with blood tests and occasionally imaging.

This happens, and there are several explanations worth ruling out.

Your free testosterone may be low even with a normal total, if most of it is bound to SHBG.

Androgen insensitivity means tissues respond poorly to testosterone despite adequate levels.

Other hormones can produce identical symptoms, including prolactin, thyroid hormones, and growth hormone.

Other conditions do too. Obesity, diabetes, sleep apnoea, chronic stress, and depression all cause low libido, fatigue, and erectile difficulties.

So can medication. Opioid painkillers, oral glucocorticoids, and some antipsychotics interfere with testosterone production or function.⁶⁵

Persistent symptoms with normal results deserve a proper evaluation rather than reassurance.

Most men stay on TRT for at least 12 months, but it depends on the cause.⁸⁵

If low testosterone is due to testicular failure or another irreversible cause, levels won't hold without continued treatment, so TRT is intended to be lifelong.

If the cause is potentially reversible, obesity or type 2 diabetes for example, you may be able to maintain normal levels without TRT once that's been treated.

Treatment is sometimes stopped early because of side effects.

Yes, when prescribed by a licensed clinician for a medical reason.

TRT is the same substance as an anabolic steroid at a much lower dose, so anabolic steroids are Class C drugs and it's illegal to supply, sell, import, or export testosterone outside medical approval.

It's also banned in most professional sport, because testosterone is performance enhancing.⁸⁶ Detectable levels can mean a multi-year ban. A Therapeutic Use Exemption is granted only rarely, for a genuine diagnosed condition such as hypogonadism.⁸⁷

TRT is for men with diagnosed hypogonadism, to restore testosterone to normal levels. Only around 20% of men with hypogonadism are actively treated.⁸⁸

Use among men without hypogonadism has also risen.⁸⁹ An estimated 25% to 50% of new users have never had a pre-treatment blood test.⁹⁰ That's worth knowing if you're comparing providers.

The aim of treatment is to correct the symptoms of deficiency and maintain normal sexual characteristics. For many men the practical goal is simpler: feeling like themselves again.⁹¹

Four main ways: injections, oral tablets, topical gels, and skin patches. Implantable pellets exist but are rarely used.⁹²

Injections are given weekly at most, producing a peak after the injection then a gradual decline. Tablets, gels, and patches are taken daily and give steadier levels without the spikes.

No method is better. They have near-equal effectiveness at restoring normal levels.⁹³ The choice comes down to preference, convenience, cost, and how likely you are to stick with it.

Blood levels normalise fast. Symptoms take longer, and it varies by symptom.

In most studies at least half of participants reached normal testosterone somewhere between 10 days and 6 months. One study measuring after a single day found 53% already in range.

Sexual function responds first. Studies of 8 weeks or less report significant improvements in erectile function and libido. Mood and quality of life tend to follow in a similar window.

Physical changes are slower. Small improvements in body composition appear within 6 months, but the noticeable gains in muscle mass and bone density come after a year or more.

Response is largest in men who started lowest, particularly below 8 nmol/L. Men without low testosterone to begin with see no meaningful improvement in sexual function. Around two-thirds of men with hypogonadism who start TRT get symptomatic benefit and complete at least 12 months.

Like any medicine, TRT has side effects worth knowing before you start:

Reduced sperm production. Raised haematocrit, meaning thicker blood. Breast tissue enlargement. Mood changes. Worsening sleep apnoea. Reduced HDL cholesterol. Fluid retention. Prostate symptoms. Acne. Male pattern hair loss. Skin reactions, with gels and patches.

Your clinician should assess your risk before starting and monitor you during treatment.⁹⁴ If side effects appear, the response is usually to adjust the dose, change the formulation, add a supporting treatment, or stop.

Seek urgent care for chest pain, breathlessness, or swelling and pain in one leg. Those can indicate a clot.

On the benefit side: better bone density, more muscle mass and physical function, and maintained sexual function. Together those tend to mean a better quality of life as you age.

On the risk side: prostate growth, which can worsen benign prostatic hyperplasia, and suppressed sperm production. Cardiovascular risk was a longstanding concern, though the TRAVERSE trial has since addressed much of it. See Q61.

Both sides argue for the same thing: regular monitoring with a clinician rather than treatment you set and forget.

TRT carries a labelled warning for venous thromboembolism, clots in the veins.⁹⁵

Guidelines advise against TRT if your haematocrit is 48% to 50% or above, if you have a family history of venous thromboembolism, or if you've been diagnosed with thrombophilia.⁹⁶,⁹⁷

Those thresholds come largely from clinical observation rather than trial data.⁹⁸ The reasoning is that TRT raises haemoglobin, and in animal studies raised haemoglobin thickens blood.⁹⁹ Whether that translates to humans is less certain.

In practice, haematocrit is monitored. Above 54% means stopping TRT or changing the dose or formulation.

Get urgent medical help for swelling, pain, or redness in one leg, chest pain, or sudden breathlessness.

There's no strong evidence that it does. More prostate cancer is detected in men on TRT, but that may be because they're screened more often. Subclinical prostate cancer is common in older men, so more biopsies find more of it.⁹⁶

Observational studies have found no significant association between testosterone levels and prostate cancer risk.¹⁰⁰,¹⁰¹ Reviews of TRT in men with previous or active localised prostate cancer haven't produced clear evidence either way.¹⁰²

Given that uncertainty, the standard advice stands: TRT isn't prescribed to men with prostate cancer. If you have a history of prostate problems, discuss it before starting.

Yes. TRT suppresses sperm production. Around 40% of men on TRT have no sperm in their ejaculate.¹⁰³

Fertility usually returns after stopping, but the recovery period varies and there's no guarantee. For that reason TRT isn't prescribed to men who are actively trying to conceive.

There are options if you want both. Selective oestrogen receptor modulators such as clomiphene, or low-dose hCG, can be prescribed alongside treatment, and both have been shown to increase sperm concentration and total count.¹⁰⁴,¹⁰⁵,¹⁰⁶

Sperm banking before starting is the other route, freezing sperm for later use in IVF or IUI.

Not for everyone.

TRT shouldn't be prescribed if you have prostate or breast cancer, are actively trying to conceive, have a haematocrit above 54%, or have severe chronic heart failure. Clinicians may also judge the risks to outweigh the benefits based on your history and other treatments.

For everyone else, age isn't the barrier. TRT is MHRA-approved for men with hypogonadism at all stages of life, including from birth for congenital conditions. Regular monitoring is strongly recommended, particularly with cardiovascular risk factors or prostate problems.

Mostly through body composition.

TRT increases muscle protein synthesis and produces small to moderate increases in fat-free mass, even without exercise. Men with low testosterone see higher than average muscle growth, with the biggest effects when treatment is combined with consistent resistance training over a year or more.¹⁰⁷ Injections tend to produce more muscle gain than gels, because the temporary spike in testosterone is more anabolic than a steady release.¹⁰⁸

Body fat and waist circumference tend to fall, though total weight only drops slightly once muscle gain is accounted for, roughly 3 kg over two years.¹⁰⁹ Some of that fat loss may simply follow from having more muscle and more energy.¹¹⁰

Claims about a wider jaw or broader shoulders come from self-reports, not studies. Where genuine, they'd apply to adolescents treated for delayed puberty, not fully developed adults.

That depends on where you're starting from.

Most men report better mood, and sometimes fewer symptoms of low mood or anxiety. More energy, better body composition, and improved sexual function all contribute indirectly.

Responses vary a lot and are hard to predict before treatment starts. Men who begin with the lowest levels and the most symptoms generally notice the biggest change.

Around two-thirds of men with low testosterone who start TRT get symptomatic benefit and complete at least 12 months of treatment.⁸⁵

The reported benefits are better libido and sexual function, better mood, better body composition, better physical function, and better quality of life overall.

How much you notice depends on your starting point. If your libido and mood were already good, there's less to improve. The strongest responses are consistently in men with the lowest baseline levels and the largest increases on treatment.¹¹¹,¹¹²

Sexual symptoms are the most specific signs of low testosterone: reduced libido, erectile dysfunction, and delayed sexual development. Multiple high-quality trials have shown significantly greater improvements in libido, erectile function, and sexual activity with TRT than placebo in men with low testosterone.¹¹¹,¹¹³,¹¹⁴

The Sexual Function Trial within the TTrials, one of the largest, found consistent improvement in 10 of 12 measures of sexual activity in men aged 65 and over, particularly frequency of intercourse and nocturnal erections.¹¹⁵,¹¹²

For erectile dysfunction specifically, TRT significantly improves erectile function, most clearly in mild cases.¹¹⁶,¹¹⁷ Combining testosterone with a PDE5 inhibitor such as sildenafil works better than the PDE5 inhibitor alone.¹¹⁸

The information for this is conflicting. Low energy is one of the most common symptoms of low testosterone. One study found lack of energy was the strongest predictor of low testosterone in men under 40.¹¹⁹

But the Testosterone Trial, the largest controlled study of TRT, produced mixed results: a statistical benefit on a vitality measure, no meaningful difference on a fatigue measure.¹²⁰,¹¹⁵ Some reviews conclude TRT doesn't affect vitality.¹²¹ Reviews of quality of life, which include energy questions, tend to find a benefit.¹²²

If TRT helps your energy, it's most likely if you started with low levels and genuine fatigue. It isn't something to count on.

Testosterone is typically reduced in major depressive disorder and bipolar disorder, and men on androgen-deprivation therapy for prostate cancer show anxiety, fatigue, and low vitality.¹²³,¹²⁴ Which direction that runs isn't clear.

On current evidence, TRT has a small positive effect on mood and quality of life in older men with hypogonadism.¹²⁵,¹²⁶ It appears to help men with late-onset, low-grade, persistent low mood, but not men with clinical depression.¹²⁷,¹²⁸ The largest analysis, covering 1,890 men across 27 trials, found the effect clearest in those with milder symptoms.¹²⁹

TRT is not a treatment for depression. If you're being treated for depression, keep taking what you've been prescribed.

Poor sleep is associated with low testosterone, and 24 to 48 hours of sleep deprivation measurably reduces levels.¹³⁰ Testosterone in turn affects circadian rhythm and sleep timing.¹³¹ Some studies suggest the link is largely explained by body fat, since low testosterone and obesity travel together.¹³²

Studies of TRT and sleep quality report a slight benefit, based on a subset of questionnaire items.¹³³

One caution: TRT may induce or worsen obstructive sleep apnoea.¹³⁴ If you have severe sleep apnoea, tell your clinician before starting.

The evidence conflicts, and it's worth knowing that before you start.

Testosterone has been linked to better memory, possibly by improving energy production in nerve cells and reducing beta-amyloid plaques.¹³⁵ Impaired memory is one of the non-specific signs of low testosterone, though whether that's the hormone or the associated chronic illness isn't clear.

One review of high-quality trials concluded TRT does not significantly improve cognition in memory-impaired older men with low testosterone.¹³⁶ Another found it may improve short-term verbal memory over 3 months, measured by story recall, but not other types.¹³⁷

Too few studies exist to be confident either way. Treat memory improvement as a possible bonus, not a reason to start.

Sometimes, and it depends heavily on why yours is low.

Weight is the clearest lever. In men with obesity-related low testosterone, a low-calorie diet significantly raised levels, and the amount of weight lost predicted how much testosterone rose.¹³⁸

Correcting a deficiency in zinc, magnesium, or vitamin D may produce small increases, though this rests on a few small studies.¹³⁹ Worth avoiding: very low-fat diets, heavy alcohol intake, and very low-calorie diets if you're already a healthy weight.¹⁴⁰,¹⁴¹,¹⁴²

One important caveat. Lifestyle change isn't a substitute for TRT if you have hypogonadism. Correcting the biochemistry doesn't always resolve the symptoms.¹⁴³ In men with obesity and hypogonadism given major weight reduction plus either TRT or placebo for 12 months, only the TRT group felt better.¹⁴⁴ Guidelines therefore recommend lifestyle change alongside TRT, not instead of it.¹⁴⁵

A few matter: insulin, oral anticoagulants, and corticosteroids.

You usually won't need to stop them. Your clinician may monitor you more closely or adjust doses.

Tell whoever prescribes your TRT about everything you take, including supplements and herbal products. There's no strong evidence those interact, but it's the kind of thing that's better on record.

Three things get checked: whether it's working, whether it's causing problems, and whether you're taking it as prescribed.⁹⁶,¹⁴⁶

Blood testosterone and haematocrit are measured at 3 to 6 months, then again at 12 months. Symptoms and side effects are reviewed at every appointment.

If you're at higher risk of prostate cancer and agree to prostate monitoring, that means PSA and a digital rectal examination 3 to 12 months after starting. A PSA rise of more than 1.4 ng/mL, or a level above 4.0 ng/mL in the first year, usually prompts a urology referral.

Monitoring is more frequent if your levels were very low, you have several symptoms, or you take medicines that interact with TRT.

It depends on your formulation.

On daily tablets, gels, or patches, a missed dose means testosterone dips for no more than about 24 hours. Take the next dose as normal.

On injections given weekly or monthly, a missed dose can mean symptoms returning for longer, closer to how you felt before treatment.

Don't double up to compensate. If you're missing doses regularly, tell your clinical team. Sometimes a different formulation fits your routine better, and that's a fixable problem rather than a failure.

Two measures: your blood levels, and how you feel.

Blood testosterone within the normal range confirms the dose is right. Improvement in the symptoms you started with confirms the treatment is doing its job. Changes in muscle mass or fasting blood sugar may also show up, though those are rarely the point.

Levels normalise quickly. Symptoms take longer, and if nothing has shifted, the dose or the formulation may need adjusting. That's a conversation worth having rather than waiting out.

On the best available evidence, no.

This was debated for years. Some studies found no effect or improvement, others found arterial plaque progression and cardiovascular events serious enough to stop trials early.¹⁴⁷,¹⁴⁸

Then in 2023 the TRAVERSE trial reported. It's the largest TRT trial assessing cardiovascular risk: over 5,000 men with hypogonadism who either had cardiovascular disease or were at high risk, randomised to TRT or placebo, treated for nearly 2 years with 3 years of follow-up. There were no significant differences in any primary cardiovascular outcome, and the TRT group had a non-significant 16% lower rate of cardiovascular death.¹⁴⁹

Two findings from TRAVERSE still warrant caution: a 46% increased risk of venous thromboembolic events, and a statistical increase in non-fatal arrhythmias and atrial fibrillation.

So cardiovascular assessment before starting matters, particularly if you already have risk factors.

There's nothing specific to TRT. Where diet does matter is cause. Guidelines stress lifestyle change alongside TRT as first-line treatment, particularly if your low testosterone is driven by obesity or type 2 diabetes, because reversing that may eventually remove the need for treatment.¹⁴⁵

If you're aiming for muscle, bone, or performance gains, protein intake is worth attention. Current recommenda

Contact your clinical team, and be specific. Tell them what you're experiencing, how long it's been going on, whether you've been following the treatment plan, and whether anything else has changed.

Depending on their assessment, you may need a review. The usual response is lowering the dose, trying a different formulation, or addressing something else contributing to the symptoms.

For anything urgent, chest pain, breathlessness, severe bleeding, or swelling and pain in one leg, go to A&E or an urgent care centre straight away. Don't wait for a callback.