Low Testosterone: Which Symptoms Actually Count, How the Test Must Be Done and Why Fertility Comes First
Tired, heavier round the middle, less interested in sex, not sleeping properly, nothing much to say for yourself. That list describes genuine testosterone deficiency. It also describes a stressful job, poor sleep, too much alcohol, undiagnosed sleep apnoea, depression, an underactive thyroid and ordinary middle age.
An entire industry lives in that overlap, and it sells testosterone to men who do not need it while the men who do need it go years without a diagnosis.
So this page is about separating the two: which symptoms actually point at testosterone, how the test has to be done to mean anything, and what has to be settled before anyone starts treatment.
⚠️ The question that must be answered before the first capsule, because it is the one that cannot be undone.
Testosterone replacement suppresses sperm production. It switches off the signal from the brain that tells the testicles to work, and sperm counts fall — sometimes to zero. In most men this recovers after stopping, and in some it takes many months, and in a minority it does not fully return.
So: if you want children now or at any point in the future, do not start testosterone without discussing it. There are treatments that raise your own production instead of replacing it, and that conversation has to happen first rather than afterwards.
🚩 Which symptoms actually mean something
The list usually given is long and almost useless because most of it is non-specific. Split properly, it becomes informative.
| More specific to low testosterone | Present in low testosterone and in everything else |
|---|---|
| Loss of morning erections | Fatigue and low energy |
| Reduced sexual desire — not performance, desire | Low mood, irritability |
| Fewer spontaneous erections | Poor concentration |
| Testicles smaller or softer than before | Loss of muscle, more body fat |
| Loss of body or facial hair, shaving less often | Reduced strength and stamina |
| Breast tenderness or enlargement | Poor sleep |
| Hot flushes, in more severe deficiency | Reduced motivation |
| Infertility | Aches and reduced recovery |
The practical rule: the three sexual items clustering together — low desire, loss of morning erections, fewer spontaneous erections — is the strongest pointer there is. The right-hand column on its own points at almost nothing, which is why fatigue alone is a poor reason to measure a hormone and a good reason to check thyroid, iron, sleep and mood.
Worth separating out, because it causes a lot of wasted treatment: low desire and erectile difficulty are different problems. Testosterone drives desire. Erections depend mostly on blood vessels and nerves, which is why tablets for erectile dysfunction work regardless of testosterone level, and why normal desire with poor erections points elsewhere — see our guide to erectile dysfunction as a vascular signal.
🧪 How the test has to be done
More men are misdiagnosed by a badly taken test than by anything else in this subject, and the rules are simple.
- 🌅 Morning, between about 7 and 11 am. Testosterone peaks on waking and falls through the day, so an afternoon sample is uninterpretable. A low result from a 4 pm blood draw means nothing at all
- 🍽️ Fasting, because eating lowers it temporarily
- 🔄 Two separate samples on different days. Levels vary day to day, and a single low reading is not a diagnosis. Around a third of men with one low result have a normal second one
- 🤒 Not during an acute illness or shortly after one, which suppresses it temporarily
- 📊 Along with LH and FSH, which separate a testicular problem from a pituitary one — and that distinction changes the whole plan
| Total testosterone | Interpretation |
|---|---|
| Below 300 ng/dL (about 10.4 nmol/L) | Deficiency, if symptoms are present and the result is confirmed |
| 300 to 350 (10.4 to 12) | Grey zone. Free testosterone or SHBG helps here — obesity, diabetes and age all lower SHBG and distort the total |
| Above 350 (12) | Deficiency unlikely. Look at the other causes below |
Two more results worth having. LH and FSH high with low testosterone means the testicles themselves are failing — primary hypogonadism. LH and FSH low or normal means the signal from the pituitary is the problem, and that warrants a prolactin level and sometimes pituitary imaging, because a pituitary tumour can present exactly this way and is treatable.
🔎 What lowers testosterone and can be reversed
This is the most valuable section on the page, because fixing any of these avoids a lifelong prescription.
| Cause | What to do |
|---|---|
| Excess weight — the single largest reversible cause. Fat tissue converts testosterone into estrogen, and central obesity suppresses the pituitary signal | Weight loss raises testosterone measurably. Around 10 percent of body weight produces a meaningful rise, and it is the only intervention here that fixes the cause rather than replacing the hormone |
| Obstructive sleep apnoea | Must be found before starting treatment, because testosterone makes apnoea worse. Snoring, breathing pauses, unrefreshing sleep — see our guide to sleep apnoea |
| Opioid painkillers | Strongly suppress production with long-term use. Frequently the whole explanation |
| Anabolic steroid use, current or past | Shuts down natural production, sometimes for a year or more after stopping. Has to be asked about honestly, because it changes the diagnosis entirely |
| Alcohol, in quantity | Direct suppression |
| Glucocorticoids | Dose and duration related |
| Type 2 diabetes and metabolic syndrome | Strongly associated — see our guide to type 2 diabetes |
| Chronic poor sleep | Most testosterone is produced during sleep. A few weeks of short sleep lowers it measurably |
| Serious chronic illness, kidney or liver disease | Treat the underlying condition |
And the honest consequence of that table: a heavy, poorly sleeping man with untreated apnoea who is told he has low testosterone and started on replacement has had the wrong problem treated. His level is low because of the other three things, and replacing the hormone leaves all of them running.
👶 Fertility, in detail
Returning to the point at the top, because it is the one most often skipped in a hurry.
Replacement testosterone tells the brain that there is plenty of testosterone, so the brain stops sending LH and FSH —> and those are the signals that drive sperm production. The result is a falling sperm count, often to zero, within months.
- 🔄 Usually reversible after stopping, over six to twelve months or longer
- ⚠️ Not always fully reversible, particularly after prolonged use
- ✅ Alternatives exist for men with secondary hypogonadism who want fertility — clomiphene and hCG raise your own production rather than replacing it, and preserve sperm counts. These are specialist decisions
- 🧪 Sperm banking before starting is worth discussing if there is any doubt
- 🚫 Testosterone is not a contraceptive. Suppression is incomplete and unpredictable, and pregnancy on it does happen
💊 Cernos: the one practical point that decides whether it works
Cernos (Testosterone Undecanoate) is oral testosterone in 40 mg soft capsules, used for confirmed male hypogonadism. Its advantage over injections and gels is obvious: no needles, and no risk of transferring hormone to a partner or child by skin contact, which is a real problem with gels.
📌 It must be taken with a meal containing fat.
Oral testosterone undecanoate is absorbed through the lymphatic system rather than directly into the bloodstream, and that absorption depends on dietary fat being present. Taken on an empty stomach, or with a low-fat meal, very little of it gets in.
This is the commonest reason the capsules appear not to work, and it is entirely avoidable. Take each dose with a proper meal, not with coffee on the way out of the door.
Dosing is typically 120 to 160 mg daily in two divided doses for the first two to three weeks, then adjusted down to a maintenance dose, commonly 40 to 120 mg daily, guided by blood levels and symptoms. Divided dosing matters because the effect is short-lived — this is not a once-weekly depot.
The trade-off compared with injections is that levels fluctuate more through the day, which some men notice and some do not. Timing the blood test consistently relative to a dose is therefore important when checking the level.
🩸 Monitoring, which is not optional
This is the part that separates proper treatment from a supplement habit, and skipping it is where the real risks sit.
| What is checked | Why |
|---|---|
| Full blood count, specifically haematocrit | The most important one. Testosterone increases red cell production, and a haematocrit climbing above the mid-fifties thickens the blood and raises clot risk. It is managed by lowering the dose or stopping, and it is found only by looking |
| Testosterone level | To confirm it is in range rather than guessing from how you feel |
| PSA and prostate assessment | Before starting and during, in men over 40. Testosterone does not appear to cause prostate cancer, and it can accelerate one that is already present and undetected |
| Blood pressure | Can rise |
| Lipids and liver function | Routine surveillance |
The usual schedule is at three months, six months, twelve months, then annually. Alongside that, report worsening snoring or daytime sleepiness, leg swelling, acne or oily skin, breast tenderness, and mood changes or irritability, all of which are dose-related and all of which respond to adjustment rather than needing the treatment abandoned.
🚫 Who should not take it
- 🚫 Anyone wanting children now or in the foreseeable future, without first discussing alternatives
- 🚫 Prostate cancer or breast cancer
- 🚫 Untreated severe sleep apnoea — treat that first
- 🚫 Haematocrit already raised
- 🚫 Severe heart failure, or a recent heart attack or stroke
- 🚫 A partner who is pregnant or trying to conceive, where a gel is being considered — not an issue with capsules, which is one of their advantages
- ⚠️ Caution with significant urinary symptoms from an enlarged prostate, and with a personal or family clotting history
📈 What to expect, and by when
Knowing the sequence prevents both impatience and false hope.
- 🔹 Three to six weeks — sexual desire and mood usually respond first
- 🔹 Three months — energy, and the level should be confirmed in range by now
- 🔹 Three to six months — body composition begins to shift, muscle up and fat down, and only if training and eating support it
- 🔹 Up to six months — erections, where they were going to improve at all
- 🔹 Six months to years — bone density
And the honest checkpoint: if there has been no meaningful benefit by six months with levels confirmed in the normal range, the diagnosis was probably wrong. At that point the useful move is to go back to the other causes rather than to raise the dose.
❌ The industry around this, and what to ignore
Worth saying plainly, because the search results for this topic are dominated by it.
- 🏥 Clinics that diagnose deficiency from a single afternoon blood test and a symptom questionnaire are diagnosing almost everyone. The questionnaire items are the non-specific column above
- 💊 Testosterone boosters and herbal supplements do not raise testosterone to any clinically useful degree. Where a product does work, it usually turns out to contain an actual hormone
- 🧪 Saliva hormone testing is not validated for this
- 📈 Treating a normal level produces no benefit and retains all the risk — the suppressed fertility, the raised haematocrit, the dependence on a prescription for life. That is the whole argument for doing the test properly
And one thing that genuinely does work and gets dismissed: resistance training and weight loss. In an overweight man with a borderline level, those two raise testosterone and improve every symptom in the right-hand column at the same time.
🔗 What else to check at the same time
Because the symptom list overlaps so heavily, the productive appointment covers more than one hormone.
- 🩸 Thyroid function, full blood count and ferritin, vitamin D, HbA1c — every one of these produces the same fatigue
- 😴 Sleep apnoea screening, which is both a cause and a contraindication
- 🧠 Mood, since low testosterone and depression share most of their symptoms and either can be the primary problem — see our guide to low drive and apathy
- 💛 Desire specifically, which is covered in our guide to reduced libido
- 🩺 Blood pressure, lipids and waist measurement, because low testosterone travels with cardiovascular and metabolic risk
And if erections rather than desire are the problem, a PDE5 inhibitor such as tadalafil works regardless of testosterone level — the two are separate treatments for separate problems, and taking testosterone for an erection problem with a normal level does not help.
📞 When to seek help
🚨 Urgently: pain, swelling or warmth in one calf, or sudden breathlessness or chest pain, while on testosterone — the raised red cell count increases clot risk. Also: severe headache with visual change, which in the context of a pituitary cause needs assessing.
Before starting:
- If you want children now or later — this is the conversation to have first
- If you snore or stop breathing at night — get that assessed first
- If you have ever used anabolic steroids — say so, because it changes the diagnosis
- If you are over 40 — ask for PSA and prostate assessment first
- If your only test was taken in the afternoon, or there was only one — ask for a proper repeat
Worth an appointment:
- Low desire with loss of morning erections and fewer spontaneous erections — the cluster that actually points here
- Testicles becoming smaller or softer, or breast tenderness
- Low testosterone with low or normal LH and FSH — ask for prolactin, and whether pituitary imaging is indicated
- On treatment with no blood count checked — chase it rather than assume
- Worsening snoring, ankle swelling, acne or irritability on treatment — all dose-related and all fixable
- No benefit after six months with confirmed normal levels — time to revisit the diagnosis, not the dose
- Taking long-term opioids with these symptoms
- Fatigue as the only symptom — ask for thyroid, iron, vitamin D and HbA1c before a hormone panel
❓ Frequently asked questions
Which symptoms actually suggest low testosterone?
Reduced sexual desire, loss of morning erections and fewer spontaneous erections clustering together is the strongest pointer, along with smaller testicles, loss of body hair and breast tenderness. Fatigue alone points at almost nothing.
When should a testosterone test be taken?
Fasting, in the morning between about 7 and 11, and repeated on a second day because levels vary. An afternoon sample is uninterpretable, and a single low reading is not a diagnosis.
Does testosterone replacement cause infertility?
Yes. It suppresses the brain signals that drive sperm production, often to zero. Usually reversible after stopping over six to twelve months, not always fully. Anyone wanting children should discuss alternatives first.
What level counts as low?
Below about 300 ng/dL or 10.4 nmol/L on two confirmed morning samples, with symptoms. Between 300 and 350 is a grey zone where free testosterone or SHBG helps. Above 350 makes deficiency unlikely.
Why must Cernos be taken with food?
Oral testosterone undecanoate is absorbed through the lymphatic system and that depends on dietary fat. Taken on an empty stomach very little gets in, which is the commonest reason the capsules seem not to work.
Can losing weight raise testosterone?
Yes, and it is the largest reversible cause. Fat tissue converts testosterone into estrogen and central obesity suppresses the pituitary signal. Around 10 percent of body weight produces a meaningful rise.
Why does sleep apnoea matter here?
Because it lowers testosterone and testosterone makes it worse, so it must be found and treated before replacement starts. Snoring, witnessed breathing pauses and unrefreshing sleep are the clues.
What blood tests are needed during treatment?
Haematocrit above all, because testosterone raises red cell production and thickens the blood, plus testosterone level, PSA over 40, blood pressure, lipids and liver function. At three, six and twelve months then annually.
Will testosterone fix my erection problem?
Only if the problem is desire rather than the erection itself. Erections depend on blood vessels and nerves, which is why tablets for erectile dysfunction work regardless of testosterone level.
Do testosterone boosters work?
Not to any clinically useful degree, and where a product does appear to work it usually contains an actual hormone. Resistance training and weight loss do raise it, particularly in overweight men.
📑 Sources and editorial
- Endocrine and urology society guidelines on the diagnosis and management of testosterone deficiency in men, including diagnostic thresholds, the requirement for fasting morning sampling and repeat confirmation
- Guidance on measurement of luteinising hormone and follicle stimulating hormone to distinguish primary from secondary hypogonadism, and on prolactin measurement and pituitary imaging in secondary cases
- Literature on the limitations of total testosterone where sex hormone binding globulin is altered by obesity, diabetes and age, and on the role of free testosterone
- Studies of diurnal variation in serum testosterone and of day-to-day variability, including the proportion of men with a single low result whose repeat is normal
- Evidence on reversible causes of low testosterone, including obesity, obstructive sleep apnoea, opioid therapy, glucocorticoids, alcohol, prior anabolic steroid use and sleep restriction
- Trials of weight reduction and of resistance exercise on serum testosterone in overweight men
- Literature on suppression of spermatogenesis by exogenous testosterone, time to recovery after discontinuation, and the use of clomiphene and human chorionic gonadotropin where fertility is to be preserved
- Prescribing information for oral testosterone undecanoate, including the requirement for administration with food containing fat, divided dosing, titration and monitoring
- Guidance on haematocrit monitoring during testosterone therapy and management of erythrocytosis, and on prostate surveillance including PSA before and during treatment
- Evidence on testosterone therapy and obstructive sleep apnoea, and on cardiovascular and thrombotic considerations
- Expected time course of response to testosterone replacement across sexual, mood, body composition and bone outcomes
- Reviews of over-the-counter testosterone booster supplements and of salivary hormone testing
- Related reading: reduced libido, erectile dysfunction as a vascular signal, erectile dysfunction treatment, obstructive sleep apnoea, low drive and apathy
- Related products: Cernos (Testosterone Undecanoate), Cialis (Tadalafil), Tadacip (Tadalafil), mens health category
- RXshop Editorial Team — reviewed by Michael Reeves, MD, FACS — Urologist & Men’s Health Specialist
Medical Disclaimer: The information in this article is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek guidance from a qualified healthcare provider with any questions you may have regarding a medical condition, and before starting, stopping or changing any medication.