Testogel (testosterone gel) is prescribed for men with clinically confirmed testosterone deficiency to alleviate symptoms such as fatigue and reduced energy. However, some patients report experiencing tiredness during treatment, which may seem contradictory. Can Testogel cause fatigue? Whilst asthenia (physical weakness) is listed as an uncommon side effect in the Summary of Product Characteristics, fatigue during treatment may also indicate suboptimal dosing, inadequate absorption, or coexisting medical conditions. Understanding the relationship between testosterone replacement and energy levels is essential for optimising therapy. This article examines the evidence, explores potential mechanisms, and provides guidance on when to seek medical review.

Can Testogel Cause Fatigue?

Testogel (testosterone gel) is a hormone replacement therapy prescribed to men with clinically confirmed testosterone deficiency, also known as hypogonadism. While the primary purpose of testosterone replacement is to alleviate symptoms of low testosterone—which often include fatigue, reduced energy, and diminished vitality—some patients report experiencing fatigue during treatment. This may seem paradoxical, but the relationship between Testogel and fatigue is more nuanced than it initially appears.

According to the Testogel Summary of Product Characteristics (SmPC), asthenia (abnormal physical weakness or lack of energy) is listed as an uncommon side effect, occurring in less than 1 in 100 patients. This term encompasses what many patients might describe as fatigue. Individual responses to hormone replacement can vary considerably. Some men may experience temporary tiredness during the initial adjustment period as their body adapts to changing hormone levels. Conversely, persistent or worsening fatigue during Testogel treatment may indicate inadequate dosing, underlying health conditions, or other factors unrelated to the medication itself.

It is important to distinguish between fatigue as a symptom of untreated testosterone deficiency and fatigue that emerges or persists despite treatment. NICE Clinical Knowledge Summary guidance emphasises that testosterone replacement should be initiated only after two separate morning testosterone measurements confirm deficiency, alongside relevant clinical symptoms. If fatigue continues or worsens after starting Testogel, this warrants clinical review to assess treatment response, exclude other causes, and optimise therapy. Patients should not stop or change their dose without consulting their prescribing clinician, as symptoms may recur after stopping treatment.

Common Side Effects of Testogel

Like all medicines, Testogel can cause side effects, although not everyone experiences them. The most frequently reported adverse reactions relate to local skin reactions at the application site and effects related to testosterone's physiological actions. Understanding these helps patients distinguish expected treatment effects from symptoms requiring medical attention.

Local skin reactions are among the most common side effects, affecting up to 1 in 10 users. These include:

• Dry skin, erythema (redness), or pruritus (itching) at the application site

• Acne or oily skin, particularly on the face, chest, and back

• Contact dermatitis or irritation

These reactions are typically mild and often resolve with continued use or by rotating application sites. For Testogel 16.2 mg/g, application sites are limited to the shoulders and upper arms, while Testogel 1% (sachets) may also be applied to the abdomen as directed.

Systemic effects related to testosterone's androgenic properties may include:

• Mood changes, including increased irritability or emotional lability

• Increased haematocrit (red blood cell concentration), which requires monitoring

• Prostate-specific antigen (PSA) elevation

• Gynaecomastia (breast tissue enlargement) or breast tenderness

• Changes in libido

• Headache or dizziness

• Fluid retention and peripheral oedema, which may worsen heart failure in susceptible individuals

• Potential suppression of spermatogenesis, which may affect fertility

Important safety precautions include preventing secondary transfer of testosterone to others, particularly women and children, which could cause virilisation. Always wash hands thoroughly after application, allow the gel to dry completely, and cover the application site with clothing before close contact with others.

The MHRA has noted that the evidence for cardiovascular risk with testosterone therapy remains uncertain. Venous thromboembolism has been reported with testosterone products. Patients should seek urgent medical attention for symptoms such as leg pain/swelling or breathing difficulties.

Patients should report any persistent or troublesome side effects to their GP or endocrinologist. The MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk) allows direct reporting of suspected side effects, contributing to ongoing medication safety surveillance. Many men tolerate Testogel well, and side effects can often be managed through dose adjustment or supportive measures.

Why Fatigue May Occur During Testosterone Treatment

Several mechanisms may explain why some men experience fatigue whilst using Testogel, despite testosterone replacement typically being prescribed to address this very symptom. Understanding these factors helps clinicians and patients identify the underlying cause and implement appropriate management strategies.

Suboptimal dosing or absorption represents a common explanation. Testogel is applied topically, and absorption can vary between individuals due to differences in skin characteristics, application technique, or concurrent use of moisturisers. If serum testosterone levels remain below the therapeutic range, symptoms of hypogonadism—including fatigue—may persist. UK guidelines recommend measuring serum testosterone levels 3–6 months after initiating treatment to ensure adequate replacement. Levels should be assessed according to the specific Testogel product guidance, typically 2–4 hours after gel application for accurate assessment.

Haematological changes may also contribute. Testosterone stimulates erythropoiesis (red blood cell production), and whilst mild increases in haematocrit can improve oxygen delivery and energy levels, excessive elevation (polycythaemia) can cause symptoms including fatigue, headache, and increased cardiovascular risk. Regular monitoring of full blood count is therefore essential, particularly in the first year of treatment. If haematocrit exceeds 0.54, dose reduction or temporary discontinuation may be necessary while investigating causes.

Hormonal fluctuations during the adjustment period can temporarily affect energy levels. The hypothalamic-pituitary-gonadal axis requires time to adapt to exogenous testosterone, and some men experience transient symptoms during this phase. Additionally, conversion of testosterone to oestradiol via aromatase enzyme activity occurs naturally, and in some cases, this hormonal balance may potentially contribute to symptoms, though evidence directly linking this to fatigue is limited.

Coexisting medical conditions must always be considered. Fatigue is a non-specific symptom with numerous potential causes, including thyroid dysfunction, anaemia, diabetes, depression, sleep disorders, and chronic disease. These conditions may coexist with testosterone deficiency or emerge independently during treatment. A thorough clinical assessment, including relevant investigations, is essential to identify and address all contributing factors rather than attributing fatigue solely to Testogel.

When to Seek Medical Advice About Fatigue

Patients using Testogel should maintain open communication with their healthcare team and seek medical advice if fatigue becomes problematic or is accompanied by other concerning symptoms. Early clinical review allows for timely investigation, treatment optimisation, and exclusion of serious complications.

Contact your GP or prescribing specialist if you experience:

• Persistent or worsening fatigue despite several months of Testogel treatment

• Fatigue accompanied by breathlessness, chest pain, or palpitations, which may indicate cardiovascular complications or polycythaemia

• Severe headaches, visual disturbances, or neurological symptoms

• Signs of mood disturbance, including depression, anxiety, or significant irritability

• Unexplained weight changes, heat or cold intolerance, which may suggest thyroid dysfunction

• Excessive daytime sleepiness or witnessed apnoeas during sleep, potentially indicating sleep apnoea

• Any new or unusual symptoms that concern you

Call 999 immediately for severe chest pain or acute shortness of breath. If urgent advice is needed and your GP is unavailable, contact NHS 111.

Routine monitoring is an integral component of safe testosterone replacement therapy. UK guidelines (NICE CKS and BSSM) recommend regular assessment including:

• Serum testosterone levels at 3–6 months, then annually

• Full blood count (haematocrit/haemoglobin) at 3–6 months, then annually, with intervention if haematocrit exceeds 0.54

• Prostate-specific antigen (PSA) and digital rectal examination in men over 40 or those at increased prostate cancer risk

• Liver function tests if clinically indicated

• Bone density assessment in men with osteoporosis risk factors

Do not stop or change your dose without medical advice. If side effects are troublesome, your clinician can adjust the dose, modify the application regimen, or consider alternative testosterone formulations. Remember that fatigue during testosterone treatment is not necessarily caused by the medication itself—comprehensive evaluation ensures all contributing factors are identified and appropriately managed, optimising both treatment outcomes and overall wellbeing.

Frequently Asked Questions