Starting testosterone replacement therapy is a decision that should come with clear-eyed understanding of both the benefits and the risks. If you have been diagnosed with low testosterone and are considering TRT, or if you have recently started treatment, you deserve honest information about what side effects are possible, how likely they are, and — critically — how proper monitoring can catch problems early and keep you safe.
The reality is that TRT is a well-established medical treatment with a generally good safety profile when properly prescribed and monitored. Most side effects are manageable and dose-dependent, meaning they can be addressed by adjusting your treatment rather than stopping it entirely. But “generally safe” is not the same as “risk-free,” and the quality of your monitoring matters enormously.
This guide covers the side effects you may experience, the blood tests and clinical checks that should be part of your ongoing care, and the red flags that require prompt medical attention. It is written for men in the UK navigating TRT — whether through the NHS or private clinics — who want to approach their treatment responsibly.
Common Side Effects of Testosterone Replacement Therapy
These are side effects that a significant proportion of men on TRT experience at some point, particularly in the early months of treatment. They are generally mild, manageable, and often resolve or stabilise as the body adjusts to new hormone levels.
Acne and Oily Skin
Testosterone stimulates the sebaceous (oil-producing) glands in the skin, which can lead to increased oiliness and acne breakouts. This is one of the most common early side effects, particularly in the first three to six months of treatment. The severity varies widely — some men notice only slightly oilier skin, while others develop significant acne on the face, back, shoulders, or chest.
What helps: In most cases, acne improves over time as hormone levels stabilise. Regular cleansing with a gentle, non-comedogenic cleanser helps. For persistent or severe acne, topical treatments (benzoyl peroxide, salicylic acid, or prescription retinoids) are effective. If acne is severe and does not respond to topical treatment, your clinician may review your testosterone dose or injection frequency, as large peaks in testosterone levels can exacerbate acne. Spreading injections into more frequent, smaller doses (such as twice-weekly instead of fortnightly) can help by reducing these peaks.
Fluid Retention
Testosterone promotes sodium and water retention, which can cause mild puffiness or bloating, particularly in the face, hands, and ankles. Weight may increase by one to three kilograms due to water retention alone, which can be discouraging if you are monitoring your weight closely.
What helps: Mild fluid retention usually stabilises within the first few months. Reducing dietary sodium intake can help. Staying well hydrated (counterintuitively) supports the body’s fluid balance. If fluid retention is persistent or significant, it should be discussed with your clinician, as it can occasionally indicate a need for dose adjustment or further investigation.
Mood Changes
The relationship between testosterone and mood is complex. Most men with low testosterone experience mood improvements on TRT — reduced irritability, improved motivation, better resilience to stress, and a general sense of wellbeing. However, some men notice increased emotional reactivity, irritability, or short-temperedness, particularly if testosterone levels are pushed too high or if there are significant peaks and troughs between doses.
What helps: Mood effects are often dose-related. If you notice increased irritability or aggression, this may indicate that your levels are too high at peak, and your clinician should review your dosing. More frequent, smaller injections tend to produce fewer mood fluctuations than larger, less frequent doses. It is also important to note that mood changes on TRT should be proportionate — if you experience significant depression, anxiety, or emotional instability, this warrants clinical review.
Changes in Libido
While improved libido is one of the most commonly reported benefits of TRT, some men experience fluctuations in sexual desire, particularly during dose adjustments. Some men notice an initial surge in libido that settles to a more moderate level over time. Others find that their libido is highest mid-cycle and dips toward the end of an injection cycle.
What helps: Stable testosterone levels (achieved through frequent dosing or daily gel application) tend to produce more consistent libido. If libido is lower than expected despite adequate testosterone levels, oestradiol levels should be checked, as both very low and very high oestrogen can impair sexual function in men.
Testicular Atrophy
When exogenous testosterone suppresses the HPG axis, the testes receive less stimulation from LH and FSH. Without this stimulation, the testes can decrease in size — typically by 10 to 25 percent. This is a cosmetic issue for most men rather than a medical one, but it can be psychologically bothersome.
What helps: HCG (human chorionic gonadotropin) administered alongside TRT can maintain testicular size by mimicking LH and keeping the testes stimulated. Many private TRT clinics in the UK offer HCG as a standard adjunct for men who are concerned about testicular atrophy or who want to maintain some degree of fertility potential.
Injection Site Reactions
For men using injectable testosterone, mild pain, redness, swelling, or a small lump at the injection site is common. Oil-based testosterone preparations (which includes all injectable formulations available in the UK) can sometimes cause a localised inflammatory reaction. Post-injection soreness typically lasts one to three days.
What helps: Rotating injection sites reduces cumulative irritation. Warming the testosterone vial or ampoule to body temperature before injecting (by holding it in your hands for a few minutes) can make injection more comfortable. Injecting slowly reduces tissue trauma. If redness, pain, or swelling is increasing or accompanied by warmth and discharge, this may indicate an infection and requires medical attention.
Clinically Significant Side Effects That Require Monitoring
These side effects are less common but carry greater clinical significance. They are the primary reason why regular blood monitoring is not optional on TRT — it is essential.
Polycythaemia (Raised Red Blood Cell Count)
This is arguably the most important side effect to understand and monitor on TRT. Testosterone stimulates erythropoiesis — the production of red blood cells in the bone marrow. While a modest increase in red blood cell count is a normal physiological response to testosterone, excessive increases can raise haematocrit (the percentage of blood volume occupied by red blood cells) to levels that increase blood viscosity. Thicker blood flows less easily, raising the risk of blood clots, stroke, and cardiovascular events.
Who is at higher risk: Men who smoke, those with pre-existing cardiovascular disease, men living at high altitude, men with sleep apnoea, older men, and those on higher testosterone doses are at greater risk of developing polycythaemia on TRT.
Monitoring: Haematocrit should be checked before starting TRT (baseline), at three months, six months, twelve months, and then at least annually. Many clinicians recommend more frequent monitoring (every three to six months) for the first year. A haematocrit above 0.54 (54%) is generally considered the threshold at which intervention is needed, though some clinicians use a lower threshold of 0.50 to 0.52.
Management if haematocrit is elevated:
- Reduce testosterone dose
- Increase injection frequency (smaller, more frequent doses can produce less erythropoietic stimulation than larger, less frequent doses)
- Switch formulations (from intramuscular to subcutaneous injection, for example)
- Therapeutic phlebotomy (blood donation or venesection to reduce red blood cell volume)
- Ensure adequate hydration (dehydration artificially raises haematocrit readings)
- Address modifiable risk factors (smoking cessation, sleep apnoea treatment)
The NHS notes that polycythaemia can increase the risk of blood clots, and regular monitoring is a cornerstone of safe TRT management.
Prostate Health and PSA
The relationship between testosterone and prostate health has been a subject of significant debate and evolving understanding. Historically, there were concerns that testosterone therapy could increase the risk of prostate cancer. Current evidence does not support the view that TRT causes prostate cancer, but it is accepted that testosterone can stimulate the growth of existing prostate cancer that may be undetected.
PSA (prostate-specific antigen) is a protein produced by the prostate gland, and elevated levels can indicate prostate enlargement, inflammation, or cancer. TRT typically causes a modest increase in PSA levels as the prostate responds to improved testosterone levels.
Monitoring: PSA should be measured at baseline before starting TRT, at three to six months, and then annually. A rapid rise in PSA (increase of more than 1.4 ng/mL within any 12-month period), or an absolute PSA level above the age-appropriate reference range, should prompt further investigation, including referral to a urologist.
Important context: Men over 40 should ideally have a baseline PSA and digital rectal examination (DRE) before starting TRT. NICE guidelines on prostate cancer provide detailed recommendations on when to investigate elevated PSA levels. Your TRT clinician should be familiar with these pathways.
Cardiovascular Risk
The relationship between TRT and cardiovascular risk has been one of the most debated topics in men’s health medicine. Early observational studies raised concerns about increased cardiovascular events in men on TRT. However, more recent and better-designed studies, including the landmark TRAVERSE trial (published in the New England Journal of Medicine in 2023), have provided reassurance that TRT at physiological doses does not significantly increase the risk of major adverse cardiovascular events in men with hypogonadism and pre-existing or high risk of cardiovascular disease.
That said, cardiovascular risk assessment remains an important part of TRT management. Men with existing cardiovascular disease, those with multiple risk factors (hypertension, diabetes, dyslipidaemia, smoking, family history), and older men require particularly careful monitoring.
Monitoring: Lipid profiles (total cholesterol, LDL, HDL, triglycerides), blood pressure, and cardiovascular risk assessment should be part of baseline and ongoing TRT monitoring. Any cardiovascular symptoms (chest pain, shortness of breath, palpitations, leg swelling) should be investigated promptly.
Liver Function
Injectable and topical testosterone preparations used in modern TRT have minimal direct impact on liver function, unlike the 17-alpha-alkylated oral steroids that were associated with liver toxicity. However, liver function tests (LFTs) are included in standard TRT monitoring panels as a general health screening measure and because some medications used alongside TRT (such as oral AI or other adjuncts) can affect liver enzymes.
Monitoring: Liver function tests should be checked at baseline and periodically during treatment (typically annually or as clinically indicated).
Sleep Apnoea
Testosterone can worsen obstructive sleep apnoea (OSA) or, in some cases, may contribute to its development. The mechanism is not fully understood but may involve effects on upper airway muscle tone and central respiratory drive. Men who already have sleep apnoea or who are at high risk (obesity, large neck circumference, heavy snoring) should be monitored for worsening symptoms.
What to watch for: Increased snoring, witnessed breathing pauses during sleep (reported by a partner), excessive daytime sleepiness, and morning headaches. If these symptoms develop or worsen on TRT, a formal sleep study may be recommended. Sleep apnoea is treatable with CPAP (continuous positive airway pressure) therapy, and its presence does not necessarily mean TRT must be stopped, but it does need to be managed.
Oestrogen Management on TRT
Testosterone is partially converted to oestradiol (a form of oestrogen) by an enzyme called aromatase, which is found primarily in fat tissue. When testosterone levels increase on TRT, oestradiol levels often increase as well. A moderate increase in oestradiol is normal and actually beneficial — oestrogen plays important roles in bone health, cardiovascular function, sexual function, and mood in men.
However, excessively high oestradiol levels can cause symptoms including:
- Water retention and bloating
- Gynecomastia (breast tissue development) or nipple sensitivity
- Emotional lability or mood changes
- Reduced libido (paradoxically, both very high and very low oestrogen can impair sexual function)
- Erectile difficulties
Monitoring: Oestradiol (E2) should be included in your blood panel, particularly if you are experiencing symptoms suggestive of high oestrogen. There is no universally agreed “ideal” oestradiol level for men on TRT, but most clinicians aim to keep it within the male reference range (typically 40 to 160 pmol/L or 11 to 44 pg/mL, depending on the assay used).
Management of elevated oestradiol:
- Dose adjustment: Reducing the testosterone dose is the first-line approach, as less substrate means less conversion to oestrogen.
- Increased injection frequency: More frequent, smaller doses can produce less aromatisation than larger, less frequent doses.
- Body composition: Reducing body fat (which contains aromatase enzyme) can lower oestrogen conversion. This is a longer-term strategy but addresses the root cause.
- Aromatase inhibitors (AIs): Medications such as anastrozole can be used to reduce oestrogen levels. However, their use in TRT is increasingly debated. AIs carry their own side effects (joint pain, bone density loss, adverse lipid changes) and there is growing consensus that they should be used cautiously and at the lowest effective dose, not as a routine prophylactic measure.
The goal of oestrogen management is balance. Excessively suppressing oestrogen with aggressive AI use can be as problematic as allowing it to run too high. A good TRT clinician will monitor your levels and symptoms together, adjusting only when there is a clear clinical indication.
The TRT Monitoring Schedule: What Blood Tests and When
Regular monitoring is not an optional add-on to TRT — it is an integral part of safe treatment. Any provider who prescribes testosterone without a structured monitoring plan is not providing adequate care. Here is what a comprehensive monitoring schedule should look like:
Baseline (Before Starting TRT)
Before your first dose, the following should be established:
- Total testosterone (two separate morning samples confirming deficiency)
- Free testosterone or SHBG (sex hormone-binding globulin) to calculate free testosterone
- LH and FSH (to differentiate between primary and secondary hypogonadism)
- Full blood count (including haematocrit and haemoglobin)
- PSA (prostate-specific antigen)
- Lipid profile (total cholesterol, LDL, HDL, triglycerides)
- Liver function tests
- Kidney function (U&Es)
- HbA1c or fasting glucose (metabolic health screen)
- Oestradiol
- Prolactin (to exclude pituitary pathology in secondary hypogonadism)
- Thyroid function (TSH, free T4 — to exclude thyroid disorders that can mimic low testosterone symptoms)
- Blood pressure
- Body weight and BMI
- DRE (digital rectal examination) for men over 40 or with prostate symptoms
3 Months After Starting TRT
- Total testosterone (trough level — taken just before next injection, or in the morning for gel users)
- Free testosterone or SHBG
- Full blood count (haematocrit is the key parameter)
- PSA
- Oestradiol
- Liver function tests
- Symptom review and clinical assessment
6 Months After Starting TRT
- Repeat the 3-month panel
- Lipid profile
- HbA1c or fasting glucose
- Blood pressure
- Body weight
- Detailed symptom review
12 Months and Annually Thereafter
- Comprehensive blood panel including all parameters above
- DRE (for men over 40, annually or as clinically indicated)
- Cardiovascular risk assessment
- Assessment of bone density (DEXA scan) if indicated
- Mental health and wellbeing review
- Review of treatment goals and ongoing appropriateness of TRT
Blood should be drawn at the right time relative to your dosing schedule. For injectable testosterone, trough levels (the lowest point in your cycle, typically just before your next injection) give the most useful information for dose adjustment. For gel users, morning blood draws two to four hours after application capture peak levels.
When to Adjust Your TRT Dosage
Dose adjustments are a normal part of TRT management. Your starting dose is an educated estimate, and fine-tuning based on blood results and symptom response is expected. Adjustments may be needed if:
- Testosterone levels are too high: Trough levels consistently above the upper reference range increase the risk of side effects without additional benefit. Dose reduction or increased injection frequency may be indicated.
- Testosterone levels are too low: If trough levels are below the mid-range and symptoms persist, a dose increase may be warranted.
- Haematocrit is elevated: Reducing dose, increasing injection frequency, or switching formulation may be needed.
- Oestradiol is elevated with symptoms: Dose reduction or frequency adjustment is preferred over adding an aromatase inhibitor where possible.
- PSA rise: A significant or rapid PSA increase requires investigation before continuing treatment at the same dose.
- Persistent side effects: Any ongoing side effects that are affecting quality of life warrant a treatment review.
Red Flags: When to Seek Immediate Medical Attention
While serious complications from properly monitored TRT are uncommon, it is important to know what warrants urgent medical attention:
- Chest pain, tightness, or pressure — could indicate a cardiac event
- Sudden severe headache — could indicate a cerebrovascular event
- Sudden weakness on one side of the body, slurred speech, or vision changes — stroke warning signs
- Leg swelling, pain, or redness (particularly one-sided) — could indicate a deep vein thrombosis
- Shortness of breath or difficulty breathing — could indicate a pulmonary embolism or fluid retention
- Significant breast lump or persistent pain — requires investigation
- Severe injection site infection (increasing redness, warmth, swelling, fever, or pus)
- Difficulty urinating or significant changes in urinary function — may indicate prostate enlargement
- Severe mood disturbance, suicidal thoughts, or aggressive behaviour
If you experience any of these symptoms, seek immediate medical attention. Do not wait for your next scheduled clinic appointment.
The Importance of Regular Clinical Reviews
Blood tests are essential, but they are only part of the picture. Regular clinical reviews — ideally every three to six months in the first year and every six to twelve months thereafter — should include a conversation about how you are feeling, how the treatment is affecting your daily life, any concerns or side effects you have noticed, and whether your treatment goals are being met.
A good TRT clinician will not just react to blood results in isolation. They will consider the whole clinical picture: your symptoms, your blood work, your lifestyle, your risk factors, and your goals. TRT should be an ongoing partnership between you and your clinician, not a prescription-and-forget arrangement.
The British Society for Sexual Medicine (BSSM) and the European Academy of Andrology both recommend structured monitoring protocols for men on TRT, and any responsible provider — whether NHS or private — should follow these guidelines. If your provider is not offering regular monitoring, this is a significant concern.
Choosing a Responsible TRT Provider in the UK
The quality of monitoring you receive depends heavily on the provider you choose. Across England, Scotland, Wales, and Northern Ireland, TRT is available through GPs (who may refer to endocrinology), NHS endocrine clinics, and private TRT clinics. When evaluating a provider, consider:
- Do they require two confirmed low testosterone blood results before prescribing?
- Do they perform comprehensive baseline blood work?
- Do they have a structured monitoring schedule with regular blood tests?
- Do they discuss side effects and risks thoroughly during the initial consultation?
- Do they discuss fertility implications?
- Are they regulated by a recognised healthcare authority?
- Do they offer dose adjustments based on blood results and symptom response?
- Do they have qualified clinicians (doctors, endocrinologists, or advanced nurse practitioners) managing your care?
At Evernu, we take monitoring seriously because we understand that safe TRT is well-monitored TRT. As a RQIA-regulated healthcare provider, we build comprehensive blood testing and regular clinical reviews into every treatment plan. Our clinicians review your results in context, adjust your protocol as needed, and ensure that your treatment continues to serve your health goals safely.
If you are considering TRT or want to switch to a provider that prioritises thorough monitoring, explore our testosterone treatment service to learn how we can help.
Frequently Asked Questions
How often should I have blood tests on TRT?
At minimum, blood tests should be performed at baseline (before starting), at three months, six months, and twelve months, and then annually. Many clinicians recommend testing every three to six months during the first year to optimise dosing. Some parameters (particularly haematocrit) may need more frequent monitoring if they are trending upward. Your clinician should provide a clear schedule and explain what each test is checking for. If you are not being offered regular blood tests, this is a red flag about the quality of your care.
Is it normal to feel worse before feeling better on TRT?
Some men experience a brief adjustment period when starting TRT, during which symptoms may fluctuate. Mild water retention, acne, or mood changes can occur in the first few weeks as the body adapts to changing hormone levels. However, feeling significantly worse on TRT is not normal and should be investigated. Possible causes include incorrect dosing (too high or too low), elevated oestrogen, or unrelated health issues. Contact your clinician if you feel worse rather than better on treatment — this usually indicates that an adjustment is needed, not that TRT is failing.
Can TRT cause hair loss?
TRT can accelerate male pattern hair loss in men who are genetically predisposed to androgenetic alopecia. Testosterone is converted to dihydrotestosterone (DHT) by the enzyme 5-alpha reductase, and DHT is the primary androgen responsible for miniaturisation of hair follicles on the scalp. If you have a family history of male pattern baldness, TRT may accelerate this process. However, TRT does not cause hair loss in men who do not carry the genetic predisposition. If hair loss is a concern, discuss it with your clinician — treatments such as finasteride or minoxidil may be appropriate, though finasteride should be used cautiously as it can affect DHT-dependent benefits of TRT.
What happens if I miss a dose or injection?
Missing a single dose of testosterone gel or a single injection is unlikely to cause significant problems, but you may notice a temporary return of low testosterone symptoms (fatigue, mood dip, reduced libido) depending on the formulation. For gel users, apply your next dose at the normal time — do not double up. For injection users, take the injection as soon as practical and then resume your normal schedule. If you consistently miss doses, speak to your clinician about whether a different formulation or dosing schedule might suit your lifestyle better. Consistency is important for maintaining stable blood levels and optimal symptom relief.
Does TRT increase the risk of prostate cancer?
Current evidence does not support the view that TRT causes prostate cancer. This concern originated from observations made decades ago, but more recent large-scale studies have not demonstrated an increased incidence of prostate cancer in men on TRT. However, testosterone can stimulate the growth of existing prostate cancer, which is why PSA monitoring and age-appropriate prostate screening are essential parts of TRT management. Men with a history of prostate cancer should discuss the risks carefully with an oncologist and urologist before considering TRT. For most men without prostate cancer, TRT at physiological doses, with proper PSA monitoring, is considered safe from a prostate perspective.
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting or changing any medication. Evernu is regulated by the Regulation and Quality Improvement Authority (RQIA).
