Nebido

Testosterone

Treatment option:

Medically reviewed

Last updated on 10/01/2026

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Nebido

Quick Facts

Property	Description
Active ingredient	Testosterone undecanoate
Form	Solution for injection (Depot preparation)
Pharmacological class	Androgens (Anabolic-androgenic steroid)
Common use	Testosterone replacement therapy (TRT)
Origin	Synthetic testosterone ester

What Type of Medicine is Nebido?

Nebido is a highly specialized pharmaceutical preparation containing the active substance testosterone undecanoate, classifying it as an androgen and an anabolic-androgenic steroid. This product is categorized under the Androgens group, which addresses hormone deficiency. It is a synthetic derivative of testosterone, developed to provide hormone replacement therapy (TRT) for men diagnosed with a deficiency of endogenous testosterone.

Composition and Long-Acting Depot Form

The single active ingredient, testosterone undecanoate, is formulated as an oily solution intended for deep intramuscular injection. This compound's unique, long ester chain is a differentiating factor: it allows the medication to create a tissue reservoir, or depot preparation, that releases the hormone gradually. This extended-release action is a clinically recognized characteristic of testosterone undecanoate, as it reduces the required frequency of administration compared to other shorter-acting testosterone esters. This design provides therapeutic consistency for the patient.

General Purpose: Sustaining Hormone Balance

The therapeutic purpose of Nebido is to address clinical symptoms associated with the absence or confirmed deficiency of natural testosterone production in adult men. The testosterone undecanoate acts as a prodrug, ensuring the sustained supply of active testosterone necessary to engage the androgen receptor. This formulation is designed to maintain therapeutic testosterone levels, which helps restore the body's hormonal balance and supports the maintenance of physical and functional characteristics dependent on adequate androgen levels.

What side effects are possible with Nebido?

The official safety profile of testosterone undecanoate is structured by government regulatory authorities to detail possible adverse reactions, categorize their frequency, and define necessary safety considerations.

Adverse Reaction Categories

Category	Description
Common Effects	Side effects classified as common (may affect up to 1 in 10 patients) include polycythaemia (an abnormally high level of red blood cells), increased haematocrit and haemoglobin, acne, weight gain, and various injection site reactions (e.g., pain, discomfort, erythema).
Systemic Effects	The label documents uncommon reactions spanning multiple System-Organ Classes, such as Psychiatric Disorders (e.g., depression, irritability), Vascular Disorders (e.g., increased blood pressure, hot flush), and Reproductive System Disorders (e.g., benign prostatic hyperplasia, prostatic specific antigen [PSA] increase).
Serious Reactions	Rare but serious adverse reactions explicitly noted in regulatory documents include Pulmonary Oil Microembolism (POME), which can occur during or immediately after injection, and the risk of Venous Thromboembolism (VTE), such as deep vein thrombosis and pulmonary embolism. Suspected anaphylactic reactions (severe allergic responses) have also been reported post-injection.

Population and Safety Notes

The official labeling defines safety considerations for specific patient populations. The use of androgens in older adults may accelerate the progression of existing sub-clinical prostatic carcinoma and benign prostatic hyperplasia (BPH). Caution is also advised for patients with severe cardiac, renal, or hepatic insufficiency, as testosterone therapy can lead to oedema (fluid retention), which may be associated with congestive heart failure. Clinical signs such as persistent irritability or frequent/prolonged erections may indicate excessive androgen exposure, a safety pattern documented in the regulatory text. Contraindications include known or suspected androgen-dependent carcinoma of the prostate or male mammary gland and past or present liver tumours.

Overdose and Emergency Response

The official regulatory profile for testosterone undecanoate overdose states that the effects are generally reversible upon cessation of therapy or dose reduction. No specific antidote is known for this medication, and management focuses on symptomatic and supportive care.

Property	Official Regulatory Statement
Documented Overdose Presentations	Clinical signs suggesting excessive androgen levels include irritability, nervousness, weight gain, and prolonged or frequent erections (Priapism). Laboratory findings often show abnormally high levels of red blood cells (Polycythemia), increased haemoglobin, and increased haematocrit.
When Immediate Medical Help is Required	Treatment must be stopped immediately if severe complications occur, such as oedema with or without congestive heart failure in vulnerable patients. Immediate emergency attention should be sought if there are severe upper abdominal complaints, as this may indicate serious complications like intra-abdominal haemorrhage linked to liver tumour risk.

The most life-threatening outcomes are associated with the abuse of the medication at doses higher than those recommended, including serious cardiovascular events (such as stroke or myocardial infarction) and hepatic complications. The mandated help-seeking conditions are based on the risk of these severe, documented complications.

Therapeutic Uses of Nebido

What Nebido Treats: Main Uses and Benefits

Nebido is commonly used for Testosterone Replacement Therapy in adult men to address various health problems caused by a confirmed lack of testosterone, known as male hypogonadism. This therapy is relevant for managing conditions characterized by symptoms of primary gonadal failure or secondary (pituitary/hypothalamic) dysfunction.

The therapy is commonly used to help with managing the hormonal deficit and may assist with easing the overall symptom burden related to this chronic deficiency. The medication is commonly used to help with symptom clusters that interfere with daily functioning, including loss of lean muscle mass, decline in bone mineral density, fatigue, depressive moods, and low sexual desire.

Quick Fact: Support for Systemic Imbalance

The therapy supports patients during difficult episodes, assisting with managing symptoms related to physical discomfort and contributing to improved functional stability. As a patient-oriented benefit, the treatment is relevant for easing symptoms related to systemic imbalance.

“The therapy supports general well-being during symptomatic phases, contributing to improved day-to-day comfort and assisting in easing the overall symptom burden on quality of life.”

Regulatory References

Malta Medicines Authority Summary of Product Characteristics

Eligibility and Restrictions for Use

The eligibility for Nebido is strictly defined by official regulatory documentation and is limited to a specific population, while mandating absolute exclusions for others.

Populations for Whom Use is Allowed

Nebido is formally indicated only for adult men (aged 18 and older) who have a confirmed diagnosis of male hypogonadism (testosterone deficiency). The eligibility requires clinical symptoms to be substantiated by two separate blood testosterone measurements.

Populations for Whom Use is Contraindicated

Use of Nebido is absolutely contraindicated in the following groups:

Women (including those who are pregnant or breastfeeding).
Men with androgen-dependent carcinoma of the prostate or the male mammary gland.
Individuals with a history of past or present liver tumours.
Patients with known hypersensitivity to testosterone undecanoate or any excipients.

Age- and Condition-Specific Restrictions

Category	Regulatory Status	Constraint
Pediatric Population	Not indicated	Use in children and adolescents (under 18) has not been clinically evaluated.
Older Adults	Limited Experience	Safety and efficacy in men over 65 years of age are supported by limited data.
Severe Organ Impairment	Use with Caution	Patients with severe cardiac, hepatic, or renal insufficiency or ischemic heart disease require caution due to the labeled risk of fluid retention.
Age-Related Hypogonadism	Not established	Safety and efficacy for hypogonadism related solely to aging are not formally established.

What should I know about interactions with other medicines?

The interaction profile for Nebido is formally documented by regulatory authorities and is defined by effects on the activity and metabolism of several concurrent medications. The following statements are based strictly on official regulatory labeling.

Interactions Requiring Close Monitoring

Nebido is reported to enhance the action of oral anticoagulants, specifically coumarin derivatives like Warfarin. This pharmacodynamic effect increases the potential for changes in anticoagulant activity. Regulatory constraints require close monitoring of the International Normalized Ratio (INR) and Prothrombin Time, particularly at the beginning or end of androgen therapy.

Additive Physiological Effects

Co-administration with corticosteroids (glucocorticoids) or ACTH carries an additive risk of oedema formation (fluid retention). This use requires heightened caution, especially in patients with pre-existing cardiac, renal, or hepatic disease, as noted in the official prescribing information. Androgens may also enhance the blood-sugar lowering effects of insulin and other anti-diabetic medications, which necessitates the evaluation of reduced dosage requirements for those agents. Furthermore, concomitant use with other drugs that may increase blood pressure may lead to additional blood pressure elevation.

Metabolic and Administrative Constraints

A pharmacokinetic interaction can occur with certain microsomal enzyme inducers, such as barbiturates. These agents are documented to increase the metabolic clearance of testosterone, potentially leading to reduced systemic exposure. Finally, as an administrative restriction, the solution for injection must not be mixed with any other medicinal products.

Mechanism of Action

How Nebido Works — Mechanism of Action

Prodrug Activation and Androgen Receptor Agonism

Nebido is a long-acting ester prodrug that is slowly hydrolyzed in the body to release the active hormone, testosterone. The primary mechanism of action involves the agonistic binding of testosterone to the Androgen Receptor (AR), an intracellular nuclear receptor present in target cells. This binding serves as the molecular trigger for the drug's effects, initiating the subsequent cascade of cellular changes.

Genomic Modulation and Systemic Modulation

The testosterone-AR complex translocates into the nucleus, where it binds to specific DNA sequences (Androgen Response Elements), thereby modulating the transcription of genes central to anabolic and androgenic processes. This genomic signaling alters the rate of protein synthesis, resulting in downstream physiological consequences impacting lean body mass, fat distribution, and bone mineral density. Additionally, the mechanism includes a negative feedback loop on the Hypothalamic-Pituitary-Gonadal (HPG) axis, which suppresses the central release of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).

Dosage and Administration Information

Nebido administration is based on a precise, long-interval injection schedule to ensure sustained hormone exposure. The medication is formulated as a 1000 mg testosterone undecanoate solution delivered by deep intramuscular (IM) injection only.

Official Administration Protocol

Administration Aspect	Clinical Protocol
Route of Administration	Strictly deep intramuscular (IM) injection only.
Standard Dosing Schedule	Initial dose is 1000 mg. The second injection is given after a minimum of 6 weeks to rapidly achieve steady-state concentrations.
Maintenance Frequency	Subsequent injections are administered every 10 to 14 weeks.
Procedural Conditions	Administration must be performed very slowly, ideally over approximately two minutes, by a healthcare professional.
Dose Adjustment Principle	The 10-to-14 week interval is individually adjusted based on the measurement of serum testosterone trough levels to ensure the dose sustains hormone concentration within the normal range.

The primary principle of Nebido use is the establishment of a tissue depot, which necessitates the deep, slow IM injection performed only by a healthcare professional. This technique supports the prolonged 10-to-14 week maintenance interval. The initial 6-week follow-up injection is a standardized procedural step designed to quickly normalize testosterone levels, structuring the beginning of the treatment course. Final determination of the exact interval for each maintenance dose relies on laboratory-confirmed hormone levels, linking the dosing schedule directly to objective monitoring data.

Recent Clinical Evidence

Research evidence / Overview of Studies for Nebido (Testosterone Undecanoate)

Evidence for Use in Male Hypogonadism

This section summarizes the structure of clinical research that has explored the use of this medication in adult men diagnosed with testosterone deficiency, a condition often called male hypogonadism. The research has primarily used Randomized Controlled Trials (RCTs) and observational settings to study the drug. These studies were generally applied in research contexts involving men with confirmed low testosterone levels and associated clinical symptoms.

Researchers focused on outcomes related to systemic or functional imbalance, such as measuring changes in the level of testosterone in the blood over defined time intervals. Studies also monitored outcomes related to sexual function, mood, physical discomfort, and fatigue, which are all outcomes related to daily functioning or activity level.

Findings describe patterns observed in these studies, reporting measured maintenance of testosterone levels within a certain range. Research describes changes measured during the study period across various patient-reported outcomes describing perceived discomfort. These studies contribute to the broader evidence landscape related to the study of male hypogonadism.

Long-term Studies and Follow-up Data

This part presents the structure of extended-duration clinical trials and prospective registry studies which have followed groups of men for many years. These studies monitor the measured stability over long periods, in some cases up to 12 years. The research examined the long-term measurements of testosterone levels and the observation of outcomes related to physical discomfort and daily functioning.

However, the long-term effects are not fully established across all measured outcomes, as large-scale, long-term RCTs specifically designed for all possible long-term observations are challenging to conduct. Therefore, limited information for long-term outcomes is available for some specific health parameters.

Evidence in Special Populations and Comorbid Conditions

This section outlines what studies have evaluated for certain patient groups where evidence is often more limited. This medication was evaluated in some studies involving older adults (geriatric patients) with testosterone deficiency. Findings were mixed; some research reported observations related to the time it took to achieve and maintain measured testosterone levels in the elderly.

Data for the use of this drug in males under 18 years of age remain insufficient because the safety and effectiveness have not been established in this pediatric population. Specific subgroup findings are uncertain for many comorbid conditions, such as Type 2 Diabetes, meaning comparative evidence is lacking for certain groups.

What is Still Uncertain About the Research

This final section synthesizes the main limitations and evidence gaps within the research landscape for this drug. Follow-up durations were limited in many of the initial trials. While research is ongoing, the certainty remains low for some of the long-term effects on the cardiovascular system and other major organs.

Evidence highlights what is known—and what is still uncertain. Findings describe group patterns, and research is ongoing to establish a complete picture of outcomes in all patient groups. The research provides context but not individual predictions, as study results reflect the specific conditions under which they were conducted.

Key Studies & References Scottish Medicines Consortium (SMC) Summary of evidence on comparative efficacy/safety for Testosterone Undecanoate (Nebido)

Frequently Asked Questions (FAQ)

Common questions about Nebido (FAQ)

Q: Does Nebido have an effect on muscle mass or strength?

A: Yes, official product information indicates that the active ingredient, testosterone, works by modulating genes central to anabolic processes and the development of body musculature. This is the mechanism by which it can influence muscle mass and strength.

Q: Is it normal to have some pain at the injection site after a Nebido shot?

A: According to the official regulatory documents, injection site pain is explicitly listed as a common side effect. This means it may affect up to 1 in 10 patients following Nebido administration. Other injection site reactions, like discomfort or redness, are also commonly reported.

Q: Do you gain weight when taking Nebido?

A: Yes, weight gain is explicitly listed in the official product information as a common side effect associated with the use of Nebido. Common side effects may affect up to 1 in 10 patients.

Q: Is the injection procedure for Nebido painful?

A: Regulatory documents list injection site pain as a common side effect of the injection. While the administration is performed slowly, pain or discomfort at the injection site is a frequently reported experience.

Q: Is it possible to be allergic to Nebido?

A: Yes. Use is contraindicated if there is a known hypersensitivity (severe allergy) to the active substance or any of its excipients. Additionally, official safety data confirms that suspected anaphylactic reactions (severe allergic responses) have been reported following the injection.

Q: Are the initial effects of Nebido stronger than later effects?

A: Official information explains that the initial injection interval is shortened (to 6 weeks) in the treatment protocol. This strategy is designed to rapidly achieve the target concentration range, which is then managed by the subsequent long-interval maintenance doses.

Q: Are headaches a common side effect of Nebido?

A: Regulatory documents indicate that migraines and headaches are sometimes reported with testosterone preparations, but they are generally classified as uncommon side effects. Uncommon means they may affect up to 1 in 100 patients.

Q: What are the documented benefits of using Nebido for testosterone deficiency?

A: Official studies indicate that Nebido helps maintain testosterone levels within the normal range. Studies monitored patient outcomes related to sexual function, mood, physical discomfort, and fatigue, which are symptoms related to hypogonadism.

Q: Does Nebido have any impact on bone density?

A: Yes. The mechanism of action involves the active hormone binding to the Androgen Receptor, which modulates genes that impact bone mineral density. This means Nebido can influence the regulation of bone health.

Q: How do doctors determine if someone needs Nebido?

A: Nebido is indicated only for men with a confirmed diagnosis of male hypogonadism (testosterone deficiency). This diagnosis must be substantiated by at least two separate blood tests showing low serum testosterone measurements, alongside the presence of clinical symptoms.

Q: What are the typical expected benefits for men starting Nebido?

A: Expected benefits relate to addressing the symptoms of hypogonadism and helping to restore hormonal balance. Studies describe monitoring changes related to sexual function, mood, and reductions in fatigue and physical discomfort.

Q: How long does Nebido stay in your system after the last injection?

A: Nebido is designed as a long-acting depot that releases the hormone gradually over many weeks. The standard maximum interval between maintenance doses is 14 weeks, after which the concentrations of the hormone typically fall below the therapeutic range.

Q: Does Nebido contain peanut oil or any other common allergens?

A: Official regulatory documents list all components of the solution. Nebido contains the active ingredient dissolved in refined castor oil (a vegetable oil) and benzyl benzoate. A healthcare professional can review the full list of excipients if there are known allergies.

Q: What happens if I miss a scheduled Nebido injection?

A: Because the dosing interval is strictly guided by blood monitoring, missing an injection means the therapeutic effect may not be sustained. This necessitates re-evaluation of your hormone levels by a healthcare provider before the next injection is scheduled.

Q: Is it normal for Nebido injections to feel 'thick'?

A: Yes, this is normal. Nebido is formulated as an oily solution for injection. This specific pharmaceutical form is required to create a depot (a long-acting reservoir) in the muscle, which allows the hormone to be released slowly over a long period.

Q: Does Nebido affect cholesterol levels?

A: While testosterone is known to affect lipid metabolism and fat distribution, official regulatory documents mandate that the effects on your lipid profile (including cholesterol) be monitored periodically throughout the duration of your Nebido therapy.

Q: How is Nebido used in men with hypogonadism?

A: It is administered by a healthcare professional as a deep intramuscular injection to create a hormone reservoir in the muscle. The goal is to maintain stable therapeutic testosterone levels, with maintenance doses administered every 10 to 14 weeks, depending on blood test results.

Q: Why is Nebido given as an oil-based solution?

A: Nebido is formulated as an oily solution specifically to enable the creation of a tissue depot (reservoir) in the muscle after injection. This depot allows the active hormone to be released gradually over many weeks, providing its characteristic long-acting effect.

Q: What research supports the efficacy of Nebido for TRT?

A: Efficacy is supported by clinical trials, including Randomized Controlled Trials (RCTs), conducted on men with confirmed testosterone deficiency. These studies have measured and reported the maintenance of serum testosterone levels within the normal range and monitored patient-reported outcomes for changes in symptoms like fatigue and mood.

Q: Is hair loss a common side effect of Nebido?

A: Regulatory documents indicate that hair loss (or alopecia) and other skin changes have been reported with testosterone preparations. These effects are generally classified as uncommon side effects.

Q: Are there any specific foods or supplements to avoid while on Nebido?

A: Official product information is silent on specific foods or routine supplements. However, it does list known interactions with certain medications, such as oral anticoagulants and corticosteroids, which require specific monitoring or caution.

Q: Do you need a prescription from an endocrinologist to get Nebido?

A: Nebido is a prescription-only medicine that requires a full diagnosis of hypogonadism. While it must be prescribed by a healthcare professional, regulatory labels do not restrict prescribing authority to a specific medical specialty like endocrinology.

Q: How long does it typically take to feel the effects of Nebido?

A: While the mechanism of action involves the slow release of testosterone from the depot, official information does not provide a specific timeline for the onset of symptom relief or perceived effects. The initial phase of treatment is designed to rapidly achieve stable testosterone concentrations.

Q: Does Nebido interact with blood thinners?

A: Yes. Regulatory documents specifically warn that Nebido may enhance the action of certain oral anticoagulants, such as Warfarin. This interaction necessitates close monitoring of blood clotting parameters, particularly when starting or stopping the therapy.

Q: Can Nebido help improve energy levels?

A: Studies related to Nebido monitored outcomes related to fatigue. Maintaining testosterone levels within the normal range addresses a core symptom of hormone deficiency, which may include low energy.

Q: Can Nebido affect fertility in men?

A: Testosterone affects the body's hormonal systems. Its mechanism includes a negative feedback loop that suppresses the central release of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), which are necessary for sperm production and fertility.

Q: What are the long-term side effects associated with Nebido use?

A: Regulatory documents state that while the drug has been studied for extended periods, the long-term effects are not fully established across all measured outcomes. Research certainty remains low for some long-term observations, such as those related to the cardiovascular system.

Q: Are there any reported interactions between Nebido and alcohol?

A: Official regulatory documents list interactions with specific medications (like anticoagulants and corticosteroids) but are silent on any formal interaction or warning between Nebido and alcohol consumption.

Q: What are the signs of having too much testosterone from Nebido?

A: The official safety label documents that clinical signs such as persistent irritability or frequent/prolonged erections may indicate that your body has excessive androgen exposure from the medication.

Q: Can Nebido be used by older men?

A: Nebido was evaluated in some studies involving older adults. Official information notes that safety and efficacy in men over 65 are supported by limited data, and caution is advised for this population due to risks like the acceleration of existing sub-clinical prostate issues.

Q: Does Nebido cause any problems with sleep?

A: While sleep issues are not directly listed, regulatory documents list psychiatric disturbances, such as depression and irritability, as uncommon systemic reactions. These effects may sometimes be associated with disruptions to sleep.

Q: Does Nebido affect mood or emotional stability?

A: Yes, regulatory documents list uncommon systemic reactions spanning Psychiatric Disorders. These can include changes in mood or emotional stability, such as reported instances of depression and irritability.

Q: Can Nebido lead to changes in prostate size?

A: Yes, Nebido may cause an increase in the prostate's size. Official documents list benign prostatic hyperplasia (BPH) and an increase in prostatic specific antigen (PSA) as uncommon side effects.

Q: Is Nebido safe to use if I have an existing heart condition?

A: Official labeling advises caution for patients with existing heart conditions, specifically severe cardiac insufficiency or ischemic heart disease. This is due to the labeled risk of oedema (fluid retention), which may be associated with congestive heart failure.

How should Nebido be stored and disposed of?

Nebido (testosterone undecanoate) must be stored and handled according to specific regulatory conditions to maintain stability and ensure safety.

Required Storage Conditions

Requirement	Specific Instruction
Temperature	Store the medicinal product at or below 30 C (86 F).
Protection	Must be protected from light and kept out of the sight and reach of children.
Handling	If stored cold, the solution must be warmed to room or body temperature prior to use. Inspect the vial; use only clear solutions free from particles.
Integrity	Do not use after the expiry date printed on the label. The solution is for single use only; any residue must be discarded immediately.

Official Disposal Rules

Nebido and its associated materials must not be disposed of via wastewater or household waste. Unused or expired medicine should be handled by asking a pharmacist how to throw away medicines that are no longer needed. These environmental protection measures must be followed.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.