Low Libido in Men: What to Test Before Testosterone, and the Fertility Question Nobody Mentions
Two complaints get treated as one and they are not. Low desire is not wanting to; erectile difficulty is wanting to and the body not cooperating. They have different causes, different tests and different treatments, and the commonest reason a man ends up on the wrong treatment is that the two were never separated.
This page is about the first one in men. It is also about a decision that gets made far too casually, because testosterone is easy to obtain and hard to come off.
🧪 The diagnosis, in numbers
Testosterone deficiency is one of the few things in sexual medicine with a hard laboratory threshold, and the way the sample is taken matters as much as the result.
- 🌅 Early morning, before about 10 or 11 am, and fasting. Levels follow a daily rhythm and fall through the day; an afternoon sample is close to meaningless
- 🔁 Two separate samples on different days. A single low reading is not a diagnosis, because levels vary considerably between days
- 📏 Total testosterone below roughly 300 ng/dL, which is about 10.4 nmol/L, together with symptoms, is the usual threshold. Between 300 and 400 is a grey zone where free testosterone and symptoms decide
- 🚫 Not during an acute illness, after a sleepless night or in the middle of a crisis. Any of those depress the result and produce a false diagnosis
And a low result is the beginning of the workup rather than the end of it. The follow-on tests say why, which changes what gets treated.
| Test | What it tells you |
|---|---|
| LH and FSH | High with low testosterone means the testes are the problem (primary). Low or normal with low testosterone means the pituitary or hypothalamus is — which needs explaining rather than simply replacing |
| Prolactin | Raised prolactin suppresses testosterone and causes low libido directly. See the warning below |
| SHBG and free or calculated free testosterone | Obesity, diabetes and liver disease alter the carrier protein, so total testosterone can mislead in both directions |
| Thyroid function, HbA1c, full blood count, ferritin | All produce fatigue and low desire on their own |
| Iron studies | Haemochromatosis is a treatable cause of pituitary failure and is missed routinely |
🚨 The one that must not be missed. Low libido with headaches, any change in peripheral vision, or milky nipple discharge — and low testosterone with a low LH rather than a high one — raises the question of a prolactin-secreting pituitary tumour.
It is uncommon, it is treatable with tablets rather than surgery in most cases, and the reason it matters here is specific: giving testosterone would improve the symptom and leave the tumour growing. A prolactin level costs almost nothing and belongs in the first round of tests.
🔍 The reversible causes, which come first
A large share of men found to have low testosterone have a reason for it that can be removed, and removing it raises the level without a prescription.
| Cause | Detail |
|---|---|
| Excess weight | The largest single factor. Fat tissue converts testosterone to oestrogen and suppresses the signal from the pituitary. Around 10 percent weight loss raises testosterone measurably, and more in those who start heavier. It is also the only intervention that improves the cause rather than the number |
| Opioid painkillers | Chronic use suppresses the whole axis strongly and this is enormously under-recognised. Anyone on long-term tramadol, codeine, morphine or similar with low testosterone and low libido has a likely explanation sitting in the medicine cupboard |
| Obstructive sleep apnea | Fragmented sleep lowers testosterone, and most of the daily production happens during sleep. Treating the apnea can raise it without hormones — see our guide to obstructive sleep apnea |
| Short sleep | A week of five hours a night lowers daytime testosterone in healthy young men by a substantial margin. Not subtle |
| Alcohol | Suppresses production directly and impairs liver handling of hormones |
| Previous anabolic steroid use | Can shut the axis down for a long period after stopping, sometimes permanently. Worth disclosing to a doctor however long ago it was, because it changes the diagnosis entirely |
| Steroid tablets | Long-term prednisolone suppresses the axis |
| Depression | Reduces libido independently of hormones, and the two are frequently diagnosed as each other — covered in our guide to major depressive disorder |
💊 Medicines that reduce desire
This list is worth going through before anything is added, and we include the ones we sell ourselves because leaving them out would be dishonest.
- 💊 Finasteride and dutasteride — the 5-alpha reductase inhibitors used for prostate enlargement and hair loss, including Proscar and Avodart. Reduced libido and erectile difficulty are recognised effects in a minority of users, and they can persist for a period after stopping. If symptoms began after starting one, say so rather than assuming coincidence
- 🧠 SSRI antidepressants — reduced desire and delayed orgasm are very common and dose-related. Switching within the class, or to bupropion or mirtazapine, usually resolves it
- 🩸 Beta blockers, and spironolactone, which has anti-androgen activity
- 💊 Opioids, as above
- 🧪 Antipsychotics, many of which raise prolactin
- 🚬 Cannabis with regular heavy use
👶 The fertility problem, which is the most important thing on this page
⚠️ Testosterone treatment suppresses sperm production and can cause infertility.
The mechanism is unavoidable rather than a side effect: external testosterone switches off the pituitary signals that drive the testes, and sperm production depends on those signals. Counts commonly fall to very low or zero levels within months. Testosterone is effective enough at this that it has been studied as a male contraceptive.
Recovery after stopping usually happens, and it can take six months to two years, and in some men it is incomplete. The risk is higher with longer use and with older age at starting.
Any man who may want children at any point should not start testosterone without this conversation. There are alternatives that raise testosterone while preserving fertility, described below. This gets omitted constantly, and it is not a reversible omission.
Also worth knowing: testosterone causes the testes to shrink to some degree during treatment, which is expected and usually reverses, and men on it who want a child later should consider sperm storage beforehand rather than afterwards.
🧬 Before the first dose
A deficiency confirmed on two morning samples, with symptoms, and the reversible causes addressed. Then screening, because testosterone is not a supplement.
- 🩸 Haematocrit and haemoglobin. Not started if haematocrit is already above about 50 percent
- 🔵 PSA and a prostate assessment in men over about 40, and certainly over 50. Known or suspected prostate cancer is an absolute contraindication
- 😴 Sleep apnea assessed, because testosterone makes it worse. Untreated severe apnea is a reason not to start
- ❤️ Cardiovascular review — blood pressure, lipids, and a frank look at heart failure, which is a contraindication when severe
- 👶 Fertility intentions discussed and documented
- 🧫 Liver function, and a baseline weight
📈 Cernos: the dosing, and the detail that decides whether it works
Cernos (Testosterone Undecanoate 40 mg soft gelatin capsules) is an oral form of testosterone replacement for confirmed male hypogonadism.
- 🔹 Typically 120 to 160 mg daily in divided doses for two to three weeks, then a maintenance dose of around 40 to 120 mg daily, adjusted on repeat blood levels and symptoms
- 🍔 Taken with a meal containing fat, and this is not optional. Oral testosterone undecanoate is absorbed through the lymphatic system and needs dietary fat to get there. Taken on an empty stomach or with a low-fat meal, absorption falls sharply and the treatment simply does not work. A great many reports of oral testosterone being ineffective come down to this
- 🕔 Divided doses, morning and evening, swallowed whole with the capsules not chewed
- 📊 Blood level timing matters. Oral dosing produces peaks and troughs, so the test has to be taken at a consistent interval after the dose for the number to mean anything — ask when to attend rather than going at a convenient time
- ⏳ Energy and mood often improve within three to six weeks; libido and sexual function take longer, sometimes three to six months. Judging it at four weeks is premature
The range sits in the mens health category, and the background on the hormone itself is in our guide to what testosterone is and why it falls.
🩸 Monitoring, and the number that matters most
Testosterone is a long-term treatment with a monitoring schedule attached. Skipping it is the difference between safe treatment and an avoidable complication.
| What | When | Why |
|---|---|---|
| Haematocrit | 3, 6 and 12 months, then yearly | The commonest significant adverse effect. Testosterone stimulates red cell production, thickening the blood and raising clot risk. Above 54 percent means stopping or reducing the dose and investigating |
| Testosterone level | 3 to 6 months, then yearly | Aiming for the middle of the normal range, not the top of it |
| PSA and prostate | 3 to 12 months, then per age guidance | Testosterone does not appear to cause prostate cancer, and it can accelerate an existing one. A rise needs assessing |
| Symptoms and mood | Each review | Including irritability, and worsening snoring or daytime sleepiness |
| Blood pressure and lipids | Yearly | Blood pressure can rise |
Also expect: acne and oilier skin, fluid retention, breast tenderness, and in some men increased irritability. And one point that catches people out — treatment is generally lifelong, because stopping returns you to the starting point or below, with the axis taking months to restart.
🔄 When testosterone is not the right answer
Three situations where something else is better, and all three are common.
- 👶 Fertility wanted, now or later. Clomid (Clomiphene Citrate) is used off-label in men to raise the pituitary signals and therefore the body own testosterone, which preserves sperm production rather than suppressing it. Typically 25 mg daily or on alternate days, with monitoring. It only works where the pituitary is capable of responding, meaning the secondary pattern of low testosterone with low or normal LH. This is the option that too few men are offered
- 🟡 Prolactin is raised. The treatment is a dopamine agonist such as cabergoline, which lowers prolactin and restores testosterone at the source, plus imaging of the pituitary. Testosterone on its own would mask the problem
- ⚖️ The cause is reversible. Weight, opioids, sleep apnea, alcohol, short sleep. Fixing these raises the level and improves everything else at the same time, which no hormone does
🏃 What raises it without a prescription
- ⚖️ Weight loss — the largest effect available, and dose-related
- 💤 Seven to eight hours of sleep, consistently. Most testosterone production happens during sleep, so this is not a general wellness point but a direct mechanism
- 🏋️ Resistance training and moderate aerobic exercise, with the caveat that extreme endurance volume in a calorie deficit lowers it
- 🍷 Less alcohol
- 💊 Reducing opioids where that is possible, with the prescriber
- 🚫 Not testosterone boosters. Over-the-counter products marketed for this do not raise testosterone in any meaningful way, several have been found to contain undeclared pharmaceutical ingredients, and some contain enough to cause harm. They are the worst value in this entire category
👫 Desire, and the part that is not hormonal
Hormones set the baseline and they are not the whole picture. Low desire that is clearly situational — present with one partner and not alone, or absent for months and then returning on holiday — is pointing somewhere other than the blood test. Relationship strain, resentment, performance anxiety after an episode of erectile difficulty, and simple exhaustion all reduce desire with entirely normal hormones, and testosterone will not touch any of them.
Where erectile difficulty came first and desire faded afterwards, the order matters: men stop initiating to avoid the failure, and the lost desire is protective rather than primary. That is treated by treating the erection. Similarly, where the problem is finishing too quickly rather than wanting to, our guide to premature ejaculation covers a different mechanism entirely.
One honest note on scope: this page is about men. Low desire in women has different causes — hormonal changes around the menopause, vaginal dryness and pain, thyroid disease, contraceptive and antidepressant effects, and relationship factors — and a different assessment. Testosterone thresholds and the advice above do not transfer.
📞 When to seek help
- Persistent loss of desire over weeks to months causing distress
- Low libido with headaches, visual changes or nipple discharge — ask for a prolactin level and do not accept testosterone without it
- Loss of morning erections, shrinking testes, reduced body hair, breast enlargement or hot flushes — these point to genuine deficiency rather than tiredness
- Erectile difficulty as well — worth assessing properly, since it can be an early sign of cardiovascular disease and diabetes
- Symptoms starting after a new medicine, particularly finasteride, dutasteride, an SSRI or an opioid
- Snoring, breathing pauses or daytime sleepiness — test for apnea before taking testosterone, not after
- Any wish to have children, before starting treatment rather than after
- On testosterone and never had a haematocrit check — arrange one
- Headache, chest pain, breathlessness, leg swelling or visual disturbance on treatment —> seek assessment, with clot risk in mind
- Worsening snoring, irritability or low mood on treatment
- Buying testosterone or boosters without testing and monitoring — the diagnosis and the supervision are the treatment, not the capsule
❓ Frequently asked questions
What testosterone level counts as low?
Total testosterone below roughly 300 ng/dL, about 10.4 nmol/L, on two separate early-morning fasting samples, together with symptoms. A single reading, an afternoon sample or a test taken during illness is not a diagnosis.
Does testosterone treatment affect fertility?
Yes. It suppresses the pituitary signals that drive sperm production, and counts commonly fall to very low or zero levels. Recovery after stopping can take six months to two years and is sometimes incomplete, so fertility plans must be discussed first.
Is there a treatment that raises testosterone without harming fertility?
Clomiphene is used off-label in men to raise the pituitary signals and therefore the body own testosterone, preserving sperm production. It works only where the pituitary can respond, meaning low testosterone with a low or normal LH.
Why must oral testosterone be taken with food?
Testosterone undecanoate is absorbed through the lymphatic system and needs dietary fat to get there. Taken on an empty stomach or with a low-fat meal, absorption falls sharply and the treatment does not work, which explains many reports of it being ineffective.
What has to be monitored on testosterone?
Haematocrit at 3, 6 and 12 months then yearly, since raised red cell concentration is the commonest significant effect and above 54 percent means stopping or reducing. Also testosterone level, PSA and prostate, blood pressure, lipids and symptoms.
Can I raise my testosterone without medication?
Yes, and weight loss has the largest effect, with around 10 percent producing a measurable rise. Seven to eight hours of sleep matters because most production happens during sleep, and reducing alcohol and opioids helps. Over-the-counter boosters do not.
Could my hair loss or prostate tablet be causing this?
Possibly. Finasteride and dutasteride cause reduced libido and erectile difficulty in a minority of users, and the effect can persist for a period after stopping. If symptoms began after starting one, raise it rather than assuming coincidence.
When should prolactin be checked?
In every workup for low libido, and urgently where there are headaches, changes in peripheral vision or nipple discharge, or where testosterone is low with a low rather than high LH. A prolactin-secreting pituitary tumour would be masked by testosterone.
Is low libido the same as erectile dysfunction?
No. Low desire is not wanting to; erectile difficulty is wanting to and the body not responding. They have different causes and treatments, and where erections failed first and desire faded afterwards, treating the erection is what helps.
Once I start testosterone, can I stop?
Treatment is generally long term, because stopping returns levels to the starting point or below while the suppressed axis takes months to restart. That makes the decision to begin worth taking slowly, after the reversible causes have been addressed.
📑 Sources and editorial
- Endocrine society and urological association guidance on the diagnosis and management of testosterone deficiency in men, including sampling conditions, diagnostic thresholds and monitoring schedules
- Guidance on the laboratory evaluation of hypogonadism, including LH, FSH, prolactin and sex hormone binding globulin, and the distinction between primary and secondary causes
- Studies of testosterone therapy and spermatogenesis suppression, time to recovery after discontinuation, and the use of testosterone in male contraceptive trials
- Prescribing information for oral testosterone undecanoate, including the requirement for administration with food and the pharmacokinetics of lymphatic absorption
- Reviews of erythrocytosis during testosterone therapy and of haematocrit thresholds for dose reduction or discontinuation
- Evidence on weight loss, sleep duration, obstructive sleep apnea and chronic opioid use as determinants of serum testosterone
- Reviews of off-label clomiphene citrate in men with secondary hypogonadism who wish to preserve fertility
- Reviews of hyperprolactinaemia and prolactinoma presenting with reduced libido, and of sexual adverse effects of 5-alpha reductase inhibitors and SSRIs
- Regulatory findings on undeclared pharmaceutical ingredients in over-the-counter testosterone-boosting products
- Related reading: what testosterone is and why it falls, premature ejaculation, benign prostatic hyperplasia, obstructive sleep apnea
- Related products: Cernos (Testosterone Undecanoate), Clomid (Clomiphene), 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.