Testonur: Uses, Dosage & Side Effects
A long-acting intramuscular testosterone undecanoate injection for testosterone replacement therapy in adult men with confirmed hypogonadism
Testonur (testosterone undecanoate 1000 mg/4 ml) is a long-acting intramuscular injection used as testosterone replacement therapy in adult men who have been diagnosed with hypogonadism (testosterone deficiency). The active substance is testosterone undecanoate, which is slowly released from the muscle depot and converted to testosterone in the body. Injections are given every 10 to 14 weeks by a healthcare professional, providing sustained physiological testosterone levels. Testonur is prescribed to treat symptoms including erectile dysfunction, low libido, fatigue, depression, and osteoporosis caused by documented low testosterone levels. It is not intended for use in women or children.
Quick Facts: Testonur
Key Takeaways
- Testonur (testosterone undecanoate 1000 mg/4 ml) is a long-acting injectable testosterone used exclusively for confirmed male hypogonadism, with injections given every 10–14 weeks by a healthcare professional.
- The diagnosis of hypogonadism must be confirmed by at least two separate low blood testosterone measurements plus clinical symptoms before treatment is started.
- The most common side effects are acne and injection site reactions; polycythemia (increased red blood cells) requires regular blood monitoring throughout treatment.
- Testonur must not be used in men with known or suspected prostate cancer, breast cancer, or liver tumors, and is not intended for women or children.
- Testosterone treatment may temporarily suppress sperm production; men wishing to father children should discuss fertility preservation options with their doctor before starting therapy.
What Is Testonur and What Is It Used For?
Testonur contains the active substance testosterone undecanoate, a pro-drug ester of testosterone. When injected deep into a muscle (typically the gluteal region), the oily solution forms a depot from which testosterone undecanoate is gradually released over several weeks. Once in the bloodstream, esterases cleave the undecanoate ester bond, releasing free testosterone and undecanoic acid (a naturally occurring fatty acid). This sustained-release mechanism provides stable testosterone levels for 10 to 14 weeks after a single injection, making Testonur one of the longest-acting testosterone formulations available.
Testosterone is the primary male sex hormone (androgen) and is essential for normal development and maintenance of male sexual characteristics. It is produced mainly by the Leydig cells in the testes under the control of luteinizing hormone (LH) from the pituitary gland. Testosterone plays critical roles in the development of male reproductive organs, maintenance of muscle mass and bone density, regulation of fat distribution, production of red blood cells, maintenance of sexual function and libido, and support of mood and cognitive function. When the body fails to produce adequate testosterone—a condition known as male hypogonadism—replacement therapy with exogenous testosterone becomes necessary to restore these physiological functions.
Male hypogonadism can be classified into two main types. Primary hypogonadism (hypergonadotropic) occurs when the testes themselves are damaged or dysfunctional, resulting from conditions such as Klinefelter syndrome, undescended testes, orchitis (testicular inflammation), testicular trauma, or previous chemotherapy or radiation. Secondary hypogonadism (hypogonadotropic) results from problems in the hypothalamus or pituitary gland that lead to insufficient stimulation of the testes, which can be caused by pituitary tumors, Kallmann syndrome, obesity, opioid use, or other conditions affecting the hypothalamic-pituitary axis.
Testonur is prescribed to treat the following symptoms of testosterone deficiency in adult men, confirmed by at least two separate blood testosterone measurements showing below-normal levels:
- Erectile dysfunction: Difficulty achieving or maintaining erections sufficient for sexual activity, which is often one of the earliest and most distressing symptoms of testosterone deficiency.
- Reduced libido: A noticeable decrease in sexual desire and interest, which can significantly impact quality of life and intimate relationships.
- Infertility: Impaired spermatogenesis (sperm production) related to gonadal dysfunction. However, it is important to note that exogenous testosterone itself can suppress sperm production (see Fertility section below).
- Fatigue and reduced energy: Persistent tiredness and decreased physical stamina that are not explained by other medical conditions.
- Depressed mood: Low mood, irritability, difficulty concentrating, and reduced motivation that are associated with testosterone deficiency.
- Osteoporosis: Reduced bone mineral density caused by low testosterone levels, increasing the risk of fractures. Testosterone plays a key role in maintaining bone health in men.
According to the Endocrine Society Clinical Practice Guidelines (2018), testosterone replacement therapy should only be initiated after a thorough clinical evaluation, including a detailed history, physical examination, and at least two morning blood testosterone measurements confirming deficiency. The guidelines emphasize that testosterone therapy should not be prescribed to men who are trying to conceive, as exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis and can reduce or halt sperm production.
Testonur must only be prescribed after testosterone deficiency has been confirmed by both clinical symptoms and at least two separate blood tests showing low testosterone levels (typically measured in the morning when levels are highest). Self-diagnosis or treatment based on symptoms alone is not appropriate, as many symptoms of low testosterone overlap with other medical conditions.
What Should You Know Before Using Testonur?
Contraindications
There are several absolute contraindications to using Testonur. These are situations in which the medication must not be used under any circumstances:
- Allergy: Do not use Testonur if you are allergic to testosterone undecanoate or any other ingredient in the product, including benzyl benzoate or refined castor oil.
- Androgen-dependent cancer: Testonur is contraindicated if you have or are suspected of having prostate cancer or male breast cancer. Testosterone can stimulate the growth of these hormone-sensitive tumors.
- Liver tumors: Do not use Testonur if you have or have ever had a liver tumor (benign or malignant), as androgenic compounds have been associated with hepatic neoplasms.
- Use in women: Testonur is not intended for use in women. It must not be used during pregnancy or breastfeeding, as testosterone can cause virilization of a female fetus and may pass into breast milk.
Warnings and Precautions
Before starting treatment with Testonur, tell your doctor if you have or have ever had any of the following conditions, as they may require additional monitoring or caution:
- Epilepsy: Testosterone may lower the seizure threshold in some patients. Close monitoring is required.
- Heart, kidney, or liver disease: Testosterone can cause fluid retention, which may worsen heart failure, kidney dysfunction, or liver impairment. Patients with severe cardiac, hepatic, or renal insufficiency may develop edema with or without congestive heart failure.
- Migraine: Testosterone may exacerbate migraines in susceptible individuals.
- Sleep apnea: Testosterone therapy may worsen obstructive sleep apnea, particularly in patients with risk factors such as obesity or chronic lung disease. The Endocrine Society recommends screening for sleep apnea before initiating testosterone therapy.
- Cancer history: If you have any form of cancer, your doctor may need to monitor blood calcium levels regularly, as testosterone can affect calcium metabolism.
- High blood pressure: Testosterone can elevate blood pressure. Your doctor will monitor your blood pressure during treatment.
- Blood clotting disorders: If you have hemophilia, thrombophilia, or other coagulation disorders, tell your doctor before each injection, as there is a risk of bleeding or hematoma at the injection site.
- Risk factors for blood clots: Testosterone therapy has been associated with venous thromboembolism (VTE), including deep vein thrombosis and pulmonary embolism. Risk factors include previous VTE, smoking, obesity, cancer, immobility, family history of clotting disorders, and advancing age.
Contact your doctor or go to the nearest emergency department immediately if you experience: painful swelling in a leg or sudden skin color changes (pale, red, or blue); sudden shortness of breath or unexplained cough (possibly with blood); sudden chest pain; severe dizziness or lightheadedness; severe abdominal pain; or sudden vision loss. These may be signs of a venous or arterial thromboembolism.
Your doctor will perform blood tests before and during treatment, including measurement of testosterone levels and a complete blood cell count. Particular attention is paid to hematocrit and hemoglobin levels, as testosterone stimulates erythropoiesis (red blood cell production), and polycythemia (abnormally high red blood cell count) is one of the most common adverse effects of testosterone therapy. The Endocrine Society recommends checking hematocrit at baseline, at 3–6 months, and then annually. If hematocrit rises above 54%, treatment should be withheld until levels return to a safe range.
Prostate and Breast Monitoring
Male hormones can accelerate the growth of prostate cancer and benign prostatic hyperplasia (BPH). Before starting treatment with Testonur, your doctor will perform examinations to rule out prostate cancer, including a digital rectal examination (DRE) and measurement of prostate-specific antigen (PSA). During treatment, your prostate and breast tissue will be examined regularly—at minimum once a year, and twice yearly if you are older or have risk factors. Any significant rise in PSA, new urinary symptoms, or breast changes should be reported promptly.
Muscle Building and Doping
Testonur must not be used for the purpose of enhancing muscle mass or athletic performance in individuals who do not have a medical need for testosterone replacement. Testosterone is classified as a prohibited substance by the World Anti-Doping Agency (WADA), and using Testonur will result in a positive doping test. Misuse of testosterone, especially at supratherapeutic doses or in combination with other anabolic androgenic steroids, can cause serious cardiovascular events (including heart attack and stroke), liver damage, psychiatric disturbances (aggression, psychosis), and physical dependence with withdrawal symptoms upon discontinuation.
Pregnancy and Breastfeeding
Testonur is not intended for use in women and must not be used during pregnancy or breastfeeding. Exposure to exogenous testosterone during pregnancy can cause masculinization (virilization) of a female fetus, including abnormal development of the external genitalia. There is no clinical scenario in which Testonur would be prescribed to a pregnant or breastfeeding woman.
Fertility
Treatment with testosterone preparations, including Testonur, can temporarily reduce or completely suppress sperm production (spermatogenesis). This occurs because exogenous testosterone suppresses the release of gonadotropins (LH and FSH) from the pituitary gland via negative feedback, which in turn reduces the intratesticular testosterone concentration needed for spermatogenesis. This suppression is generally reversible, and sperm production typically returns to baseline within 6–18 months after discontinuation of treatment, although recovery time can vary. Men who are planning to father children should discuss this with their doctor before starting Testonur, as alternative treatments that preserve fertility (such as clomiphene citrate or human chorionic gonadotropin) may be more appropriate.
Children, Adolescents, and Elderly Patients
Testonur is not intended for use in children or adolescents under 18 years of age. There are no clinical data supporting its use in this population, and exogenous testosterone can cause premature closure of the epiphyseal growth plates, potentially resulting in reduced adult height. In elderly patients over 65, no dose adjustment is generally needed, but more frequent monitoring of prostate health, hematocrit, and cardiovascular risk factors is recommended.
Driving and Operating Machinery
Testonur has not been observed to impair the ability to drive or operate machinery. However, patients should be aware that some side effects of testosterone therapy, such as dizziness or fatigue, could theoretically affect alertness. If you experience such symptoms, exercise caution when driving or performing tasks requiring concentration.
How Does Testonur Interact with Other Drugs?
Drug interactions are an important consideration with any testosterone preparation. Testonur can alter the effects of other medications, and other medications can influence how testosterone works in the body. Always inform your healthcare provider about all medications you are currently taking, have recently taken, or might take, including prescription drugs, over-the-counter medications, and herbal supplements.
Clinically Significant Interactions
| Drug / Class | Interaction | Clinical Action |
|---|---|---|
| ACTH & Corticosteroids | Increased risk of fluid retention (edema), especially in patients with heart or liver impairment | Monitor for signs of edema; dose adjustment may be needed |
| Oral anticoagulants (coumarins) | Testosterone may enhance the anticoagulant effect, increasing bleeding risk | INR monitoring required; anticoagulant dose may need reduction |
| Insulin & antidiabetic agents | Testosterone can increase insulin sensitivity, potentiating the hypoglycemic effect | Blood glucose monitoring; antidiabetic dose adjustment may be necessary |
| SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin) | Combined use with testosterone may increase red blood cell count (polycythemia) more than either agent alone | More frequent hematocrit and hemoglobin monitoring required |
Additional Considerations
Testosterone may affect certain laboratory tests, including thyroid function tests. If you are undergoing blood work, always inform the laboratory staff that you are receiving Testonur. Additionally, if you have any coagulation disorder, inform your doctor before each injection, as intramuscular injections carry a risk of bleeding or hematoma formation in patients with bleeding diatheses.
The product contains benzyl benzoate (2000 mg per 4 ml vial, equivalent to 500 mg/ml) as an excipient. While this is generally well tolerated in adult patients, benzyl benzoate can cause allergic reactions in some individuals. The castor oil base may also rarely cause hypersensitivity reactions.
What Is the Correct Dosage of Testonur?
Testonur is administered exclusively by intramuscular injection and must be given by a trained healthcare professional. The injection is given very slowly into a large muscle (typically the gluteal muscle), taking care to avoid injecting into a blood vessel. Accidental intravascular injection can cause serious adverse reactions including pulmonary oil microembolism (see Side Effects section).
Adults
Standard Dosing Regimen
Dose: 1000 mg testosterone undecanoate (one 4 ml vial) per injection
Loading phase: First injection at baseline, second injection at 6 weeks
Maintenance: One injection every 10–14 weeks thereafter
Route: Deep intramuscular injection (gluteal), administered very slowly
| Phase | Timing | Dose | Notes |
|---|---|---|---|
| 1st Injection | Day 1 (baseline) | 1000 mg / 4 ml | Baseline testosterone levels measured before injection |
| 2nd Injection | Week 6 | 1000 mg / 4 ml | May be given earlier to rapidly achieve therapeutic levels |
| Maintenance | Every 10–14 weeks | 1000 mg / 4 ml | Interval adjusted based on trough testosterone levels |
Your doctor will measure your blood testosterone level at the end of each injection interval (the “trough” level) to determine whether the dosing interval is optimal. If trough levels are below the normal range, injections may be given more frequently (closer to 10 weeks). If trough levels are above normal, the interval may be extended (closer to 14 weeks). It is important that you attend all scheduled injection appointments to maintain stable testosterone levels.
Children and Adolescents
Testonur is not indicated for use in children or adolescents under 18 years of age. There are no clinical data to support its use in pediatric populations. The use of exogenous testosterone in young patients can cause premature epiphyseal closure (early fusion of growth plates), potentially resulting in permanently reduced adult height, as well as precocious puberty.
Elderly Patients
No specific dose adjustment is needed for men over 65 years of age. However, the Endocrine Society and EAU guidelines recommend more careful screening and monitoring in elderly patients, including regular assessment of prostate health (DRE and PSA), cardiovascular risk factors, and hematocrit levels. The decision to initiate testosterone therapy in older men should weigh the potential benefits against the risks, as the risk-benefit profile may differ from that in younger hypogonadal men.
Missed Dose
If you miss a scheduled injection appointment, contact your doctor’s office as soon as possible to reschedule. Do not try to “double up” on doses. Your doctor will determine the best time for your next injection based on how long it has been since your last dose and your current testosterone levels.
Overdose
Since Testonur is always administered by a healthcare professional in a controlled setting, overdose is unlikely. However, symptoms of excessive testosterone levels include irritability, nervousness, weight gain, and persistent or frequent erections (priapism). If you experience any of these symptoms, contact your doctor, who may extend the injection interval or temporarily discontinue treatment. There is no specific antidote for testosterone overdose; management is symptomatic and supportive.
What Are the Side Effects of Testonur?
Like all medicines, Testonur can cause side effects, although not everybody experiences them. The side effects listed below are based on data from clinical trials and post-marketing surveillance. The frequency categories follow the standard medical convention established by the Council for International Organizations of Medical Sciences (CIOMS).
Common
May affect up to 1 in 10 patients
- Polycythemia (abnormally high red blood cell count)
- Weight gain
- Hot flushes
- Acne
- Prostate enlargement (benign prostatic hyperplasia) and related symptoms
- Injection site reactions (pain, bruising, irritation, induration)
Uncommon
May affect up to 1 in 100 patients
- Allergic reactions
- Increased appetite, changes in blood glucose or lipid levels
- Depression, emotional disturbance, insomnia, restlessness, aggression, irritability
- Headache, migraine, tremor
- Cardiovascular events, hypertension, dizziness
- Bronchitis, sinusitis, cough, dyspnea, snoring, voice changes
- Diarrhea, nausea
- Altered liver function tests
- Hair loss, pruritus, skin redness, dry skin
- Joint pain, limb pain, muscle spasms, myalgia, muscle stiffness, elevated creatine phosphokinase
- Urinary disturbances (decreased flow, incomplete emptying, nocturia)
- Prostate disorders (prostatic intraepithelial neoplasia, prostate induration, prostatitis), altered libido, testicular pain, gynecomastia, elevated sex hormones
- Fatigue, general weakness, excessive sweating, night sweats
Rare
May affect up to 1 in 1,000 patients
- Pulmonary oil microembolism (POME): This occurs when small amounts of the oily injection solution enter the bloodstream and reach the lungs. Symptoms include sudden coughing, shortness of breath, malaise, excessive sweating, chest pain, dizziness, tingling sensations (paresthesia), or fainting. These reactions occur during or immediately after injection and are generally transient and reversible. Patients are monitored during and after each injection for these symptoms.
- Suspected anaphylactic reactions after injection
Additionally Reported with Testosterone Products
Reported during post-marketing experience
- Nervousness, hostility
- Sleep apnea (temporary cessation of breathing during sleep)
- Skin reactions including seborrhea (oily skin) and dandruff
- Increased body hair growth
- More frequent erections
- Jaundice (very rare; yellowing of the skin and eyes)
- Priapism (persistent painful erection; rare, associated with testosterone replacement in severe hypogonadism)
- Fluid retention and edema
- Suppression of spermatogenesis (reduced sperm production) at high doses
One of the most clinically significant risks of testosterone therapy is polycythemia (elevated red blood cell count, hematocrit, and hemoglobin). This increases blood viscosity and the risk of thromboembolic events (blood clots). Your doctor will perform regular blood tests to monitor these values. If hematocrit exceeds 54%, treatment should be suspended until levels normalize. According to the Endocrine Society guidelines, hematocrit should be checked at baseline, 3–6 months after starting treatment, and at least annually thereafter.
If you experience any side effect not listed here, or if any side effect becomes severe, contact your doctor or nurse. Reporting side effects helps improve the safety information available for this medicine.
How Should You Store Testonur?
Keep Testonur out of the sight and reach of children at all times. There are no special storage requirements for this medication—it can be stored at room temperature. Do not use Testonur after the expiration date (EXP) printed on the carton and label; the expiration date refers to the last day of the stated month.
At cold storage temperatures, the properties of this oil-based solution may temporarily change (e.g., increased viscosity, cloudiness). If the product has been stored in cold conditions, it should be brought to room or body temperature before use. The solution should be visually inspected before use: only clear solutions free from particles should be administered. The contents of each vial should be injected immediately after opening, and any unused solution must be discarded. Testonur vials are for single use only.
Do not dispose of medicines via household waste or wastewater. Ask your pharmacist how to properly dispose of medicines you no longer use. These measures help protect the environment.
What Does Testonur Contain?
| Component | Amount per Vial | Role |
|---|---|---|
| Testosterone undecanoate | 1000 mg (equiv. 631.5 mg testosterone) | Active substance |
| Benzyl benzoate | 2000 mg (500 mg/ml) | Solvent / excipient |
| Refined castor oil | q.s. to 4 ml | Oily vehicle |
Testonur is a clear, yellowish oily solution supplied in amber glass vials. Each vial contains 4 ml of solution and is packaged in a cardboard outer carton. Pack size: 1 × 4 ml vial. The product is manufactured by Kleva Pharmaceutical S.A. and the marketing authorization is held by EQL Pharma AB.
The oily castor oil vehicle provides the depot effect, enabling slow release of testosterone undecanoate from the intramuscular injection site over a period of weeks. Benzyl benzoate serves as a co-solvent to keep the testosterone undecanoate in solution. Both excipients are well-established in intramuscular depot formulations.
Frequently Asked Questions About Testonur
Testonur contains testosterone undecanoate, which is a long-acting ester that only needs to be injected every 10–14 weeks. This is significantly less frequent than shorter-acting testosterone esters such as testosterone enanthate or testosterone cypionate, which typically require injections every 1–4 weeks. The longer injection interval with Testonur provides more stable blood testosterone levels and is more convenient for many patients. However, Testonur must be administered by a healthcare professional due to the large injection volume (4 ml) and the risk of pulmonary oil microembolism, whereas some shorter-acting preparations can be self-administered.
The timeline for experiencing benefits varies by symptom. Improvements in sexual interest and desire may begin within 3–6 weeks, with full effects within 6 months. Energy levels and mood may improve within 3–4 weeks. Effects on muscle strength and body composition may take 3–6 months to become apparent, with maximum benefits at 12–24 months. Effects on bone density may take up to 3 years to fully develop. The loading dose schedule (second injection at 6 weeks) is designed to achieve therapeutic testosterone levels more quickly than waiting the full 10–14 weeks between the first and second injection.
Hair loss (alopecia) is listed as an uncommon side effect of Testonur (affecting up to 1 in 100 patients). Testosterone is converted to dihydrotestosterone (DHT) by the enzyme 5-alpha-reductase, and DHT is the primary androgen involved in androgenetic alopecia (male pattern baldness). In men who are genetically predisposed to male pattern hair loss, testosterone replacement therapy may accelerate this process. Conversely, testosterone can increase body and facial hair growth. If hair loss is a concern, discuss this with your doctor, as there are treatment options available.
Long-term testosterone replacement therapy is considered safe for most men with confirmed hypogonadism when properly monitored. The Endocrine Society recommends regular follow-up including assessment of testosterone levels, hematocrit, PSA, liver function, lipid profile, and bone density. Long-term studies of testosterone undecanoate injections have shown sustained efficacy and a favorable safety profile over periods of up to 10 years, with consistent improvements in body composition, sexual function, mood, and bone density. However, ongoing monitoring is essential, as the risk of polycythemia, prostate issues, and cardiovascular events requires vigilance throughout the duration of treatment.
Yes, Testonur can significantly reduce or completely suppress sperm production (spermatogenesis). This is because exogenous testosterone suppresses the body’s own production of LH and FSH (the hormones that stimulate the testes to produce sperm). This effect is generally reversible after stopping treatment, with sperm counts typically returning to baseline within 6–18 months, although some men may take longer. If you wish to have children, it is very important to discuss this with your doctor before starting Testonur. Alternative approaches such as clomiphene citrate, human chorionic gonadotropin (hCG), or sperm cryopreservation may be recommended.
If you experience coughing, shortness of breath, dizziness, or chest discomfort during or immediately after the injection, tell your healthcare provider immediately. These could be symptoms of pulmonary oil microembolism, which is a known rare reaction that typically resolves on its own but requires monitoring. For injection site reactions such as pain, bruising, or swelling, applying a cold compress may help. If any side effect is severe, persistent, or concerning, contact your doctor. Do not skip or delay your next scheduled injection without consulting your doctor first.
References
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- Corona G, Goulis DG, Huhtaniemi I, et al. European Academy of Andrology (EAA) guidelines on investigation, treatment and monitoring of functional hypogonadism in males. Andrology. 2020;8(5):970-987. doi:10.1111/andr.12770
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