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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Other
Testosterone Undecanoate is a long-acting ester of the natural androgen testosterone, used primarily for testosterone replacement therapy in adult males with primary or hypogonadotropic hypogonadism. It is available in both long-acting injectable and oral formulations.
Name
Testosterone Undecanoate
Raw Name
TESTOSTERONE UNDECANOATE
Category
Other
Drug Count
4
Variant Count
8
Last Verified
February 17, 2026
RxCUI
1490661, 1490667, 2609597, 2609603, 2609605, 2609607, 2609609, 2609611, 2121766, 2121768, 2121770, 2121776, 2201640, 2201642, 2599054, 2599060
UNII
H16A5VCT9C
About Testosterone Undecanoate
Testosterone Undecanoate is a long-acting ester of the natural androgen testosterone, used primarily for testosterone replacement therapy in adult males with primary or hypogonadotropic hypogonadism. It is available in both long-acting injectable and oral formulations.
Detailed information about Testosterone Undecanoate
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Testosterone Undecanoate.
Testosterone Undecanoate is a potent, long-acting ester of the naturally occurring male sex hormone, testosterone. It belongs to a pharmacological class known as androgens, or more specifically, anabolic-androgenic steroids (AAS). In the clinical setting, this medication is primarily utilized for testosterone replacement therapy (TRT) in adult males who suffer from conditions associated with a deficiency or absence of endogenous (naturally produced) testosterone. These conditions include primary hypogonadism (testicular failure due to cryptorchidism, bilateral torsion, orchitis, or vanishing testis syndrome) and hypogonadotropic hypogonadism (congenital or acquired LH/FSH deficiency due to pituitary-hypothalamic injury).
According to the FDA-approved labeling history, Testosterone Undecanoate was first approved in an injectable form (brand name Aveed) in March 2014, following a lengthy review process focused on safety. More recently, the landscape of testosterone therapy was transformed with the 2019 approval of Jatenzo, the first oral formulation of testosterone undecanoate that bypassed the traditional liver toxicity issues associated with older oral androgens. This was followed by other oral versions like Tlando and Kyzatrex in 2022. Unlike shorter-acting esters like testosterone cypionate or enanthate, the undecanoate ester allows for a much longer duration of action, significantly reducing the frequency of administration for patients.
At the molecular level, Testosterone Undecanoate acts as a pro-drug. Once administered, the undecanoate ester is cleaved by endogenous esterases (enzymes that break down esters) to release the active testosterone molecule into the systemic circulation. Testosterone then exerts its biological effects by binding to the androgen receptor (AR) located in the cytoplasm of target cells in various tissues, including the prostate, testes, muscle, and adipose (fat) tissue.
Upon binding, the testosterone-receptor complex undergoes a structural change and migrates into the cell nucleus, where it binds to specific sequences of DNA called androgen response elements (AREs). This process modulates the transcription of specific genes, leading to the synthesis of proteins that mediate the androgenic and anabolic effects of the hormone. In certain tissues, testosterone is converted by the enzyme 5-alpha-reductase to dihydrotestosterone (DHT), which has an even higher affinity for the androgen receptor. In other tissues, such as the brain and bone, it is aromatized into estradiol (an estrogen), which is critical for bone density and libido. This complex signaling pathway ensures the maintenance of secondary male sex characteristics, bone health, and red blood cell production.
The pharmacokinetics of Testosterone Undecanoate vary significantly between the intramuscular (IM) injection and oral formulations, requiring healthcare providers to tailor monitoring accordingly.
The primary FDA-approved indication for Testosterone Undecanoate is for replacement therapy in adult males for conditions associated with a deficiency or absence of endogenous testosterone. This includes:
While not FDA-approved for these purposes, healthcare providers sometimes use testosterone undecanoate off-label for conditions such as constitutional delay of growth and puberty in males or certain types of gender-affirming hormone therapy, although these uses require specialized clinical oversight.
Testosterone Undecanoate is available in several distinct delivery systems:
> Important: Only your healthcare provider can determine if Testosterone Undecanoate is right for your specific condition. The choice between oral and injectable forms depends on patient preference, lifestyle, and underlying health risks.
The dosage of Testosterone Undecanoate is highly individualized based on the patient's serum testosterone levels and clinical response. Healthcare providers typically aim to maintain testosterone levels within the normal physiological range (usually 300 to 1,000 ng/dL).
Testosterone Undecanoate is generally not approved for use in pediatric patients (males under the age of 18). The safety and efficacy of this specific long-acting ester have not been established in children. Use in adolescents may cause premature closure of the epiphyseal growth plates (the ends of long bones), which can lead to permanent termination of linear growth and shorter adult stature. If androgen therapy is required for a minor, healthcare providers usually select different, shorter-acting testosterone formulations that allow for more precise titration.
No specific dosage adjustments are provided in the manufacturer's labeling for patients with renal impairment. However, because testosterone can cause fluid retention (edema), patients with pre-existing kidney disease must be monitored closely for worsening renal function or cardiovascular strain.
Specific studies in patients with hepatic impairment have not been conducted for the undecanoate ester. While the undecanoate ester does not carry the same risk of peliosis hepatis (blood-filled cysts in the liver) as 17-alpha-alkylated steroids, testosterone therapy should be used with caution in patients with known liver disease. If significant liver enzyme elevations occur, therapy may need to be discontinued.
Clinical trials of Testosterone Undecanoate did not include sufficient numbers of patients aged 65 and older to determine if they respond differently than younger subjects. Healthcare providers generally use caution in the elderly due to the increased risk of prostatic hypertrophy (enlarged prostate), prostate cancer, and cardiovascular events such as myocardial infarction (heart attack).
Proper administration is critical for the efficacy and safety of this medication:
If you miss a dose of the oral formulation, take it as soon as you remember with food. However, if it is almost time for your next scheduled dose, skip the missed dose and resume your regular schedule. Do not double the dose to catch up. If you miss an appointment for your injection, contact your healthcare provider immediately to reschedule. Consistency is key to maintaining stable hormone levels.
Acute overdose of Testosterone Undecanoate is unlikely to result in life-threatening toxicity, but chronic over-administration can lead to serious complications. Signs of excessive testosterone levels include extreme mood swings, high blood pressure, persistent erections (priapism), and significant fluid retention. In the event of a suspected acute overdose, contact a Poison Control Center or seek emergency medical attention. Treatment is generally supportive and involves discontinuation of the medication.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or frequency without explicit medical guidance, as this can lead to hormonal imbalances and increased side effect risks.
Many patients starting Testosterone Undecanoate may experience mild to moderate side effects as the body adjusts to the hormone replacement. Common reactions include:
> Warning: Stop taking Testosterone Undecanoate and call your doctor immediately or seek emergency care if you experience any of the following:
Prolonged use of Testosterone Undecanoate requires ongoing vigilance for long-term complications:
Testosterone Undecanoate carries significant FDA Black Box Warnings that vary by formulation:
Report any unusual symptoms or changes in your health to your healthcare provider immediately to ensure safe continuing therapy.
Testosterone Undecanoate is a Schedule III controlled substance under the Controlled Substances Act due to its potential for misuse and abuse. Abuse of testosterone, often in combination with other anabolic androgenic steroids, can lead to serious adverse outcomes, including heart attack, heart failure, stroke, liver disease, and psychiatric manifestations such as mania or psychosis. Patients must use this medication only as prescribed and under strict medical supervision.
As detailed in the side effects section, the FDA has issued Black Box Warnings for Testosterone Undecanoate.
Safety monitoring is a cornerstone of Testosterone Undecanoate therapy. Your healthcare provider will require regular blood tests, including:
Testosterone Undecanoate generally does not impair the ability to drive or operate heavy machinery. However, if a patient experiences dizziness or sudden coughing fits (in the case of POME following an injection), they should avoid these activities until symptoms resolve and they have been cleared by a medical professional.
While there is no direct chemical interaction between alcohol and Testosterone Undecanoate, excessive alcohol consumption can worsen many of the conditions TRT is meant to treat. Alcohol can lower natural testosterone production, increase estrogen levels, and contribute to liver strain and weight gain. Patients are advised to limit alcohol intake while on therapy.
Stopping Testosterone Undecanoate suddenly will result in a return to pre-treatment testosterone levels, which may cause a recurrence of symptoms like fatigue, low libido, and depression. Because the injectable form is long-acting, the 'washout' period is several months. There is no specific withdrawal syndrome, but patients should always consult their doctor before stopping to manage the transition and monitor hormone levels.
> Important: Discuss all your medical conditions, especially heart, liver, or kidney disease, with your healthcare provider before starting Testosterone Undecanoate.
There are few absolute contraindications for drug combinations with Testosterone Undecanoate, but certain substances should be avoided entirely to prevent severe complications:
Testosterone Undecanoate can interfere with several laboratory tests:
> Important: Tell your doctor about ALL medications, over-the-counter drugs, vitamins, and herbal products you are taking. A complete medication review is essential for preventing dangerous interactions.
There are specific clinical scenarios where the risks of Testosterone Undecanoate therapy clearly outweigh any potential benefits. In these cases, the medication must NEVER be used:
In these conditions, healthcare providers must perform a careful risk-benefit analysis and exercise extreme caution:
Patients who have had allergic reactions to other testosterone esters (like cypionate or enanthate) should be approached with caution. While the undecanoate ester is unique, the underlying testosterone molecule is the same. Furthermore, patients with a history of sensitivity to oil-based injections (like certain vitamins or other hormones) must be screened for allergies to the specific carrier oils used in the injectable formulation (Aveed).
> Important: Your healthcare provider will evaluate your complete medical history, including any history of cancer or heart disease, before prescribing Testosterone Undecanoate to ensure it is safe for you.
Testosterone Undecanoate is strictly contraindicated in women who are or may become pregnant. It is categorized as FDA Pregnancy Category X. Exposure of a female fetus to androgens results in virilization, which includes clitoral hypertrophy, labial fusion, and abnormal development of the urogenital sinus. If a woman becomes accidentally exposed to this medication during pregnancy, she must be informed of the high risk to the fetus. There is no clinical scenario where the use of this drug is justified during pregnancy.
Testosterone Undecanoate is not indicated for use in females, and there is no data regarding its presence in human breast milk. However, because of the potential for serious adverse reactions in nursing infants (such as precocious puberty or bone growth issues), it should not be used by breastfeeding individuals. Endogenous testosterone is naturally present in milk, but exogenous supplementation would likely lead to supraphysiological levels in the infant.
Safety and effectiveness in pediatric patients below the age of 18 have not been established. The primary concern in this population is the acceleration of bone maturation. Androgens can cause the epiphyseal growth plates to close prematurely, which results in a permanent loss of potential adult height. If used for delayed puberty, it must be monitored by a pediatric endocrinologist with frequent X-ray assessments of bone age (typically every 6 months).
In clinical trials, there was insufficient evidence to determine if patients over 65 respond differently than younger men. However, geriatric patients are at a higher baseline risk for several conditions that testosterone can exacerbate:
There are no formal studies of Testosterone Undecanoate in patients with renal impairment. However, since testosterone promotes the retention of sodium, chloride, potassium, and water, patients with chronic kidney disease (CKD) must be monitored with extreme care. If a patient is on dialysis, the drug is not expected to be cleared by the dialysis machine due to its high protein binding, meaning the long-acting nature of the undecanoate ester remains unchanged.
No specific dose adjustments are provided for hepatic impairment. However, because the liver is the primary site of testosterone metabolism and conjugation, patients with severe hepatic impairment (Child-Pugh Class C) may experience higher-than-expected systemic exposure. Therapy should be discontinued if signs of drug-induced liver injury (DILI) occur, such as elevated transaminases or bilirubin.
> Important: Special populations, particularly the elderly and those with pre-existing organ dysfunction, require highly individualized medical assessment and more frequent laboratory monitoring.
Testosterone Undecanoate is a fatty acid ester of the natural androgen, testosterone. Its primary mechanism of action is through the activation of the androgen receptor (AR). Once the undecanoate ester is hydrolyzed by esterases in the blood or tissues, the free testosterone molecule enters cells and binds to the AR. This complex then acts as a transcription factor in the cell nucleus, binding to androgen response elements (AREs) on the DNA. This triggers the expression of genes responsible for the development and maintenance of male secondary sexual characteristics, the stimulation of muscle protein synthesis (anabolic effect), and the stimulation of erythropoiesis (red blood cell production) in the bone marrow.
The pharmacodynamics of Testosterone Undecanoate are characterized by a steady maintenance of serum testosterone levels within the physiological range. Unlike shorter-acting injections that cause 'peaks and valleys' (high levels shortly after injection followed by low levels before the next), the undecanoate ester provides a more stable hormonal environment. The onset of effect for libido and mood improvements is typically 3-6 weeks, while changes in muscle mass and bone density may take 6-12 months of continuous therapy.
| Parameter | Value |
|---|---|
| Bioavailability | ~7% (Oral, with fat); High (IM Injection) |
| Protein Binding | 98% (40% to SHBG, 58% to Albumin) |
| Half-life | ~34 days (Injection); ~1.5 hours (Oral active T) |
| Tmax | 7-14 days (Injection); 4-6 hours (Oral) |
| Metabolism | Hepatic (Aromatase, 5-alpha-reductase) |
| Excretion | Renal 90%, Fecal 6% |
Testosterone Undecanoate is classified as an Androgen and Anabolic Steroid (AAS). It is a Schedule III controlled substance. It is therapeutically grouped with other testosterone replacement therapies, including testosterone cypionate, testosterone enanthate, and transdermal testosterone gels (e.g., AndroGel). However, its unique ester and delivery mechanisms (specifically the oral lymphatic absorption) distinguish it from other members of the class.
Common questions about Testosterone Undecanoate
Testosterone Undecanoate is primarily used for testosterone replacement therapy (TRT) in adult men who have low or no testosterone due to specific medical conditions. These conditions include primary hypogonadism, where the testes are damaged or failed, and hypogonadotropic hypogonadism, where the brain's signaling to the testes is impaired. It helps restore testosterone to normal levels, which can improve symptoms like low libido, fatigue, depressed mood, and loss of muscle mass. It is available in a long-acting injection that lasts for 10 weeks or in newer oral capsule forms. This medication is only for men with confirmed testosterone deficiency through blood tests.
The most common side effects include skin changes such as acne or increased oiliness, as well as reactions at the injection site like pain or swelling. Many patients also experience an increase in red blood cell count (hematocrit), which requires regular monitoring to ensure the blood does not become too thick. Other frequent side effects include headaches, slight increases in blood pressure, and changes in mood such as increased irritability. Some men may also notice breast tenderness or enlargement due to the conversion of testosterone to estrogen. Most mild side effects can be managed with the help of a healthcare provider.
There is no known direct drug interaction between alcohol and Testosterone Undecanoate, but moderation is strongly advised. Excessive alcohol consumption can interfere with the goals of testosterone therapy by further suppressing natural hormone production and increasing estrogen levels. Alcohol also places additional stress on the liver and can contribute to weight gain and sleep disturbances, which may worsen the symptoms of low testosterone. Furthermore, alcohol can affect blood pressure, which is a concern for those taking the oral form of this medication. It is best to discuss your alcohol consumption habits with your doctor before starting therapy.
No, Testosterone Undecanoate is absolutely unsafe during pregnancy and is classified as FDA Pregnancy Category X. If a pregnant woman is exposed to this medication, it can cause severe and permanent birth defects, specifically the virilization of a female fetus. This includes the development of male physical characteristics in a female baby. Women who are pregnant or may become pregnant should never handle or take this medication. If accidental exposure occurs, a healthcare provider should be contacted immediately. The drug is strictly intended for use in adult males only.
The timeline for seeing results from Testosterone Undecanoate varies depending on the specific symptom being treated. Improvements in sexual desire (libido) and energy levels are often noticed within 3 to 6 weeks of starting therapy. Changes in mood and quality of life typically follow a similar timeframe. However, physical changes such as increased muscle mass, decreased body fat, and improved bone density take much longer, often requiring 6 to 12 months of consistent treatment. It is important to maintain regular follow-up appointments and blood tests during this time to ensure the dosage is optimal for your body.
While stopping Testosterone Undecanoate suddenly is not typically life-threatening, it will cause your testosterone levels to drop back to their original low state. This often leads to a return of symptoms like extreme fatigue, low sex drive, and irritability. Because the injectable form (Aveed) is very long-acting, it stays in your system for several months, so the decline in hormone levels will be gradual. For the oral forms, the levels will drop much faster. You should never stop your treatment without consulting your doctor, as they may want to monitor your hormone levels or discuss alternative therapies.
If you miss a dose of the oral capsules, take the missed dose with food as soon as you remember. If it is nearly time for your next dose, skip the missed one and stay on your regular schedule; do not take two doses at once. If you miss an appointment for your long-acting injection, contact your clinic immediately to reschedule. Missing an injection can cause your testosterone levels to fall below the therapeutic range, leading to a return of symptoms. Consistency is vital for maintaining stable hormone levels and achieving the best results from your therapy.
Testosterone Undecanoate can cause changes in body weight, but this is often due to a shift in body composition. Many men experience an increase in lean muscle mass and a decrease in body fat, which may result in a higher number on the scale even if they look leaner. However, testosterone can also cause the body to retain extra sodium and water (edema), which can lead to rapid weight gain and swelling in the ankles or feet. If you notice sudden, significant weight gain or severe swelling, you should notify your healthcare provider immediately. Maintaining a healthy diet and exercise routine can help manage these changes.
Testosterone Undecanoate can interact with several types of medications, so a full review of your current prescriptions is necessary. It most notably interacts with blood thinners like warfarin, where it can increase the risk of bleeding, and with diabetes medications like insulin, where it may cause blood sugar to drop too low. It can also cause increased fluid retention if taken with corticosteroids. Always inform your doctor about all supplements, over-the-counter drugs, and prescriptions you are taking. Your healthcare provider will monitor your blood work closely to adjust doses of interacting medications as needed.
Currently, the newer oral formulations of Testosterone Undecanoate, such as Jatenzo and Tlando, are relatively new to the market and are protected by patents, meaning generic versions are not yet available. The injectable form, Aveed, also does not have a widely available generic equivalent in the United States at this time. However, in many international markets, generic versions of the 1000 mg injection (Nebido) have been available for several years. Patients should check with their insurance provider and pharmacist for the most current information on generic availability and cost-saving options.