Injectables

Testopel (Testosterone Pellets)

Updated · 26 sources

Testopel is a sterile, cylindrical subcutaneous pellet containing 75 mg of unesterified crystalline testosterone that a clinician implants under the skin of the hip or buttock. Unlike injectable esters such as testosterone cypionate or testosterone enanthate, which sit in an oil depot until esterases cleave off a fatty-acid chain, Testopel dissolves slowly in subdermal fat and releases testosterone base directly over 3 to 6 months. Approved by the US Food and Drug Administration (FDA) on July 13, 1972 under Abbreviated New Drug Application (ANDA) 080911 and marketed in the US as of November 2026 by Endo USA, it is the only FDA-approved implantable testosterone pellet.

Because placement is an office procedure and the dose cannot be easily adjusted once inserted, Testopel trades day-to-day convenience for inflexibility. It also carries procedure-specific risks of pellet extrusion (spontaneous expulsion through the incision) and implantation-site infection, alongside the systemic warnings and DEA Schedule III rules that apply to all prescription androgens. This page summarizes what the FDA label, pharmacokinetic studies and clinical trials report. It is for education only and is not medical advice.

Property Detail
Drug class Androgen; anabolic-androgenic steroid (unesterified crystalline testosterone implant)
Brand / approval Testopel (Endo USA), FDA approval July 13, 1972 (ANDA 080911); marketed in the US as of November 2026
Route Subcutaneous implantation into subdermal fat of the hip or buttock
Pellet composition 75 mg crystalline testosterone per pellet (total weight about 78 mg), 2 mg polyvinylpyrrolidone USP, 0.97 mg stearic acid NF; 3.2 mm by about 9 mm
Labeled dose 150–450 mg (2–6 pellets) subcutaneously every 3–6 months; clinical trials commonly studied 600–900 mg (8–12 pellets)
Duration of action 3–4 months in most men (up to 6 months on the label); apparent absorption half-time about 2.5 months
Testosterone content 100% of the 75 mg active dose is unesterified testosterone
Key procedure risks Implantation-site infection (cellulitis, abscess), pellet extrusion, hematoma, bruising, pain and fibrosis
US schedule Schedule III controlled substance (21 CFR 1308.13)
WADA status Prohibited at all times under S1.1 anabolic androgenic steroids (2026 Prohibited List)

What it is

Testopel consists of fused crystalline testosterone—17β-hydroxyandrost-4-en-3-one, formula C₁₉H₂₈O₂, molecular weight 288.4 g/mol (Testopel label; PubChem). Each sterile, bullet-shaped pellet is 3.2 mm (1/8 inch) in diameter and about 9 mm long, with a surface area of about 98 mm² (Testopel label; McCullough, Curr Sex Health Rep 2014). One pellet weighs about 78 mg and contains:

  • 75 mg crystalline testosterone (active hormone);
  • 2 mg polyvinylpyrrolidone USP (binder);
  • 0.97 mg stearic acid NF (lubricant).

Pellets are packaged one per sterile glass vial or ampule in boxes of 10 or 100 (Testopel label). Because the hormone is unesterified, 100% of the 75 mg active weight is testosterone, compared with about 70% in testosterone cypionate and about 63% in testosterone undecanoate.

Subcutaneous hormone implants were first described in the late 1930s (McCullough, Curr Sex Health Rep 2014). The FDA approved Testopel on July 13, 1972 under ANDA 080911 for Bartor Pharmacal (Drugs@FDA: ANDA 080911). The product saw limited use until Slate Pharmaceuticals acquired and relaunched it in 2008; ownership later passed through Actient and Auxilium to Endo USA, which markets it under the July 2025 label (McCullough, Curr Sex Health Rep 2014; Testopel label). Earlier Australian and European trials used 100 mg and 200 mg excipient-free pellets made by Organon (Handelsman et al., JCEM 1990), while US compounding pharmacies also make unapproved pellets (such as 100 mg E100 implants) (Kresch et al., Sex Med 2023). As of November 2026, Testopel remains the only FDA-approved testosterone pellet.

Pharmacokinetics and duration of effect

Unesterified testosterone in blood has a reported half-life of 10 to 100 minutes and is about 98% bound in plasma, mainly to sex hormone-binding globulin (SHBG), with about 2% free (Testopel label). About 90% of a dose leaves in urine as glucuronic and sulfuric acid conjugates, and about 6% in feces. With a pellet, duration is controlled by how slowly the solid implant dissolves in low-blood-flow subcutaneous fat (McCullough, Curr Sex Health Rep 2014).

The FDA label states that roughly one-third (33%) of the dose is absorbed in the first month, one-fourth (25%) in the second month, and one-sixth (17%) in the third month, with adequate effect lasting 3 to 4 months and sometimes up to 6 months (Testopel label).

Classical crystalline pellet studies

Because formal bioavailability studies were deferred in 1972, early human kinetic data came from Australian and German studies of 100 mg and 200 mg crystalline pellets (McCullough, Curr Sex Health Rep 2014):

Study Design & dose Key findings
Handelsman et al., JCEM 1990 43 hypogonadal men (111 implants); crossover of 6 × 100 mg, 3 × 200 mg (600 mg) and 6 × 200 mg (1200 mg) Near zero-order release of 1.5 mg/day per 200 mg pellet (95% CI 1.3–1.6) and 0.65 mg/day per 100 mg pellet; absorption half-duration 2.5 months; normal levels lasted 4–5 months (600 mg) or 6 months (1200 mg)
Jockenhövel et al., Clin Endocrinol 1996 14 men (baseline testosterone under 3.6 nmol/L); 6 × 200 mg (1200 mg) Burst peak of 49.0 ± 3.7 nmol/L at 0.5 days, plateau of 35.2–34.8 nmol/L from day 2 to day 63, then decline; apparent terminal half-life 70.8 ± 10.7 days; 95.9% absorbed by day 189
Kelleher et al., Clin Endocrinol 2004 136 men (756 implants of 4 × 200 mg = 800 mg); 112 extruded pellets weighed Release rate 1.34 ± 0.02 mg/day per 200 mg pellet (95% CI 1.30–1.37) over 3 months; mean return for reimplantation at 5.8 months

In these trials, rising testosterone increased dihydrotestosterone (DHT) and estradiol and suppressed pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) (Handelsman et al., JCEM 1990; Jockenhövel et al., Clin Endocrinol 1996).

Testopel (75 mg) decay kinetics and BMI

US studies of the 75 mg Testopel pellet found that serum testosterone peaks 1 to 4 weeks after insertion and then follows an exponential (first-order) decay as pellet surface area shrinks (McCullough et al., J Sex Med 2012; Pastuszak et al., J Androl 2012). In 273 hypogonadal men (mean age 56 ± 12.6 years, 501 insertions), Pastuszak et al. reported (Pastuszak et al., J Androl 2012):

  • Pellet number: 10–12 pellets (750–900 mg) produced higher peak total and free testosterone and higher estradiol than 6–9 pellets (450–675 mg).
  • Body mass index (BMI): men with a BMI of 25 kg/m² or more reached lower peaks—due to a larger volume of distribution—but decayed more slowly than men with a BMI under 25 kg/m².
  • Reimplantation timing: total testosterone crossed 300 ng/dL at about 100 days in both BMI groups, supporting reimplantation at 100 to 120 days (3.3 to 4 months). Preimplantation testosterone and repeat rounds (up to 4) did not change decay rates.

Approved medical use, dosing and clinic procedure

Labeled indications and limitations

Testopel is FDA-approved for replacement therapy in males with endogenous testosterone deficiency (Testopel label):

  1. Primary hypogonadism (congenital or acquired): testicular failure from cryptorchidism, bilateral torsion, orchitis, vanishing testis syndrome or orchiectomy.
  2. Hypogonadotropic hypogonadism (congenital or acquired): gonadotropic LHRH deficiency or pituitary-hypothalamic injury from tumors, trauma or radiation.
  3. Delayed puberty: brief treatment (such as 4 to 6 months) with conservative doses in carefully selected males with clearly delayed puberty not secondary to pathology who do not respond to psychological support.

Diagnosis requires morning serum testosterone below the normal range on at least two separate days before starting treatment (Testopel label). Safety and efficacy have not been established in “age-related hypogonadism” (late-onset hypogonadism), and the label states Testopel must not be used to enhance athletic performance.

Labeled dosing vs clinical practice

The 1972 label bases pellet count on prior weekly requirements of injectable testosterone propionate, whereas post-2008 US clinical studies used higher pellet counts (Testopel label; McCullough, Curr Sex Health Rep 2014):

Parameter FDA label guideline Contemporary US clinical studies
Total dose 150–450 mg (2–6 pellets) 450–900 mg (6–12 pellets; most often 10–12 pellets = 750–900 mg)
Dosing rule Two 75 mg pellets per 25 mg/week of testosterone propionate (e.g., 6 pellets for 75 mg/week; 4 pellets for 50 mg/week) Dosed by BMI and clinical response; 10 or more pellets used in 63% of pooled academic insertions
Interval Every 3 to 6 months Every 3 to 4 months (100–120 days) in most men

Sources: Testopel label; Kaminetsky et al., J Sex Med 2011; McCullough et al., J Sex Med 2012; Pastuszak et al., J Androl 2012.

Implantation procedure

Testopel is implanted in a clinic under sterile conditions (Cavender & Fairall, J Sex Med 2009; Conners et al., J Sex Med 2011):

  1. Preparation and local anesthesia: the upper outer buttock or lateral hip is cleaned with an antiseptic (such as povidone-iodine) and numbed with local lidocaine (often buffered and with epinephrine).
  2. Trocar tunnel: through a small skin incision (about 3–5 mm), a sterile trocar is advanced into the subdermal fat layer parallel to the skin to create a track 5 to 10 cm deep.
  3. Standard vs “V” technique: in the standard technique, all pellets are placed into one linear tunnel using forceps and an obturator rod. In the modified “V” technique, two caudally directed tracks angled 10 to 15 degrees apart are made through the same incision so 10 to 13 pellets sit further from the wound (Conners et al., J Sex Med 2011).
  4. Closure: brief pressure stops oozing, and adhesive skin strips and a sterile dressing close the incision without sutures.

Published clinical data

  • Phase IV open-label trial (Kaminetsky et al., J Sex Med 2011; McCullough 2014): 28 hypogonadal men received 8 pellets (n = 3), 10 pellets (n = 14) or 12 pellets (n = 11). Total testosterone stayed above 315 ng/dL in 100% of men at weeks 1 and 4, 86% at week 12, 75% at week 20, and 14% at week 24. LH fell significantly, erectile function and symptom scores improved through week 12, PSA did not change, and no extrusions or infections occurred. In a second-implant extension (22 men), 100% were above 315 ng/dL at week 4 and 31.8% at week 16.
  • Six-center cohort (McCullough et al., J Sex Med 2012): across 380 men and 702 Testopel insertions, 6 to 10 or more pellets maintained therapeutic levels (above 300 ng/dL) for 4 to 6 months, with 8 or more pellets (and especially 10–12) giving higher peaks and longer duration. Only 4 extrusions (0.6%) and 3 hematomas (0.4%) occurred.
  • Coadministration with anastrozole (Mechlin et al., J Sex Med 2014): in 38 men (65 insertions), adding off-label oral anastrozole 1 mg/day curbed estradiol rise, prevented gonadotropin suppression, and lengthened average time to reimplantation from 128 days (Testopel alone) to 198 days.
  • Randomized trial vs compounded pellets (Kresch et al., Sex Med 2023): a phase 3 noninferiority trial (NCT04523480) randomized 75 hypogonadal men to Testopel 750 mg (10 × 75 mg, n = 33, median age 54.5 years) or compounded E100 800 mg (8 × 100 mg, n = 42, median age 52.5 years):
Outcome (median, interquartile range) Testopel 750 mg (n = 33) Compounded E100 800 mg (n = 42) p value
Baseline testosterone (ng/dL) 219.5 (194.0–252.0) 202.3 (143.5–256.0) 0.2563
2-month testosterone (ng/dL) 543.0 (460.0–716.5) 696.5 (591.0–822.0) 0.1940
4-month testosterone (ng/dL) 290.0 (209.0–439.0) 277.0 (228.0–378.0) 0.7028
6-month testosterone (ng/dL) 209.0 (155.0–267.0) 241.0 (158.0–287.0) 0.5947
2-month estradiol (pg/mL) 29.1 (21.3–35.4) 42.7 (42.1–48.4) 0.0006
4-month hematocrit (%) 45.9 (42.8–48.7) 45.8 (44.4–46.8) 0.7835

By 4 months, 69% of Testopel users and 67% of E100 users had fallen below 300 ng/dL (82% overall by trial end). One extrusion occurred with Testopel (3.0%, 1 of 33) vs none with E100 (Kresch et al., Sex Med 2023).

Pellet extrusion and infection rates

The FDA label warns that implantation-site infection (cellulitis, abscess) and pellet extrusion can occur together or separately, most often within the first month after insertion (Testopel label). Rates are much lower with the 3.2 mm Testopel pellet and two-track “V” placement than with older 200 mg Organon pellets:

Study Pellet & cohort Extrusion rate Infection rate Key findings
Jockenhövel et al., 1996 200 mg pellets; 50 men, 112 implants 3 men (5 pellets) 5.4% (6 of 112) Local infections led to extrusions
Handelsman et al., 1997 200 mg pellets; 221 men, 973 procedures 8.5% (83 of 973) 0.6% (6 of 973) Extrusion linked to physical work activity (p = 0.044) and pellet count; bleeding 2.3% (22 of 973)
Kelleher et al., 2001 200 mg pellets; RCT, 96 men, 246 implants 12% hip (15 of 125) vs 5% abdomen (6 of 121) Similar by site Hip had 2.6-fold higher extrusion odds (95% CI 1.1–7.1); 2 vs 4 tracks did not alter rates
Kelleher et al., 2002 200 mg pellets; RCT, 186 men, 400 implants 9.2% gentamicin soak (18 of 195) vs 11.2% control (23 of 205) Operator-dependent Antibiotic soaking did not reduce extrusion (p = 0.42); povidone-iodine beat alcohol prep
Cavender & Fairall, 2009 Testopel 75 mg; 80 men, 292 procedures 0.3% (1 of 292) 0.3% (1 of 292) Zero infections or extrusions in men following post-procedure instructions
Conners et al., 2011 Testopel 75 mg; 168 men, 281 procedures (40 single-track vs 241 “V” track) 7.5% standard vs 0.8% “V” technique 5.0% standard vs 1.2% “V” technique “V” technique allowed 10–13 pellets with low extrusion; hematoma 0% vs 1.2% (only 1 of 59 implants on blood thinners had hematoma)
Pastuszak et al., 2012; McCullough 2014 Testopel 75 mg; 273 men, 501 insertions 1.1% 0.4% High-volume academic series

Comparison with other testosterone formulations

Clinicians and patients weigh Testopel against daily testosterone gel, weekly testosterone cypionate or testosterone enanthate injections, long-acting intramuscular testosterone undecanoate, and oral testosterone undecanoate.

Three-year comparison: gels, pellets and weekly injections

A Baylor cohort followed 178 hypogonadal men for up to 3 years on daily gels (n = 47), Testopel pellets (10–14 pellets every 3–6 months, n = 74), or weekly intramuscular cypionate/enanthate (100–200 mg/week, n = 57) (Pastuszak et al., Sex Med 2015):

Measure Transdermal gels (n = 47) Testopel pellets (n = 74) Weekly IM esters (n = 57) p value
Baseline testosterone (ng/dL, mean ± SD) 300 ± 89.6 268 ± 167.4 306 ± 164.0 0.297
Hemoglobin change at 9 months (g/dL) +0.79 ± 0.94 +0.81 ± 1.15 +1.06 ± 1.40 0.598
Hematocrit change at 9 months (%) +2.55 ± 2.6 +2.62 ± 3.5 +6.47 ± 12.4 0.074
Erythrocytosis (hematocrit over 50%) 12.8% (6 of 47) 35.1% (26 of 74) 66.7% (38 of 57) under 0.0001
Mean time to hematocrit over 50% (months) 14.0 ± 12.6 16.4 ± 10.7 10.5 ± 9.1 0.01
Baseline to final PSA (ng/dL) 0.90 to 1.02 1.24 to 1.41 0.73 to 0.73 Non-significant

Testopel had an intermediate rate of erythrocytosis (35.1%) between daily gels (12.8%) and weekly injections (66.7%), and took longest to cross 50% hematocrit (16.4 months) (Pastuszak et al., Sex Med 2015; Ohlander et al., Sex Med Rev 2018). In 158 men treated with pellets for up to 21 years (mean 8 years), higher trough testosterone—not treatment duration—predicted polycythemia (adjusted OR 15.0, 95% CI 2.5–90.8) (Ip et al., Eur J Endocrinol 2010).

Depot injections and patient preference

  • Versus intramuscular testosterone undecanoate: in a randomized crossover trial of 38 men comparing 4 × 200 mg subdermal pellets with injectable testosterone undecanoate, clinical effects on muscle mass, strength, hematology, mood and sexual function were interchangeable, but 91% chose the injection at study end (Fennell et al., Clin Endocrinol 2010). A New Zealand database of 179 men on undecanoate (124 with prior pellets) found normal trough testosterone in 72% on undecanoate vs 53% on pellets (Conaglen et al., J Sex Med 2014).
  • US patient satisfaction survey: among 382 men on TRT (52.5% injections, 30.6% gels, 16.9% Testopel), satisfaction was similar across pellets (69.8%), injections (72.5%) and gels (68.4%) (Kovac et al., J Sex Med 2014). Men chose pellets for ease of use (64.1% vs 43.8% injections and 42.6% gels) and convenience (57.8% vs 26.3% and 19.4%), with no risk of skin transfer to children or partners, whereas injections won on lower cost (34.5% vs 18.8% for pellets).

Side effects, warnings and contraindications

  • Implant-site reactions: induration, inflammation, fibrosis, bleeding, bruising, hematoma, wound drainage, pain, itching, scarring and subcutaneous nodules (Testopel label). Pain caused discontinuation in 7.5% of standard single-track vs 1.7% of “V”-track insertions (Conners et al., J Sex Med 2011).
  • Pellet dermatitis: rare erythematous plaques over the buttocks and thighs appearing within 28 days of Testopel insertion and recurring with repeat implants (Heldt Manica & Cohen, Cureus 2017).
  • Inflexibility: the label stresses that pellets are far less flexible for dose adjustment than oral or injectable forms; if testosterone must be stopped because of a complication, the pellets have to be surgically removed (Testopel label).

Systemic androgen warnings

The FDA label lists class-wide risks (Testopel label):

  • Polycythemia: periodic hemoglobin and hematocrit monitoring is required.
  • Venous thromboembolism (VTE): postmarketing reports of deep vein thrombosis (DVT) and pulmonary embolism (PE); stop Testopel immediately if VTE is suspected.
  • Cardiovascular events and blood pressure: studies on major adverse cardiovascular events (heart attack, stroke, cardiovascular death) remain inconclusive, though some report increased risk. Testosterone can raise blood pressure; monitor blood pressure periodically and avoid use in uncontrolled hypertension.
  • Prostate and breast: increased risk of prostatic hypertrophy and prostate cancer in older men; hypercalcemia from osteolysis in breast cancer patients.
  • Liver: peliosis hepatis and hepatic neoplasms (including hepatocellular carcinoma) with prolonged high-dose androgens, plus cholestatic jaundice.
  • Edema: sodium and water retention, which can worsen congestive heart failure in patients with cardiac, renal or hepatic disease.
  • Endocrine, reproductive and skeletal: gynecomastia, priapism or frequent erections, oligospermia and suppressed spermatogenesis at high doses, and premature epiphyseal closure in children and adolescents (requiring wrist/hand bone-age X-rays every 6 months).
  • Drug interactions and other reactions: enhanced anticoagulant effect (clotting factors II, V, VII and X suppressed; close monitoring on blood thinners), reduced blood glucose and insulin needs in diabetes, elevated oxyphenbutazone levels, acne, male-pattern baldness, hirsutism, headache, anxiety, depression, paresthesia, raised cholesterol and rare anaphylactoid reactions.

Contraindications

Testopel is contraindicated in men with breast cancer or known or suspected prostate cancer, in women who are or may become pregnant (Pregnancy Category X, due to fetal virilization), and in anyone hypersensitive to its ingredients (Testopel label).

Schedule III status and anti-doping

Testopel is a DEA Schedule III controlled substance (21 CFR 1308.13). The FDA label warns that abuse of testosterone and other anabolic steroids at supratherapeutic doses is linked to cardiac arrest, myocardial infarction, cardiomyopathy, heart failure, stroke, hepatotoxicity, severe psychiatric reactions (depression, mania, psychosis, hallucinations, aggression), testicular atrophy and infertility, followed by withdrawal symptoms (depression, fatigue, craving, insomnia, hypogonadotropic hypogonadism) when stopped (Testopel label).

In sport, exogenous testosterone is prohibited at all times under S1.1 Anabolic Androgenic Steroids on the WADA 2026 Prohibited List.

Key takeaways

  • The sole FDA-approved testosterone pellet. Approved July 13, 1972 (ANDA 080911) and marketed by Endo USA as of November 2026, each 3.2 × 9 mm pellet contains 75 mg of 100% unesterified crystalline testosterone.
  • Implanted in a clinic every 3 to 6 months. Placed under local anesthesia into hip or buttock fat via a trocar, Testopel eliminates daily gel transfer risks and weekly self-injections, but requires surgical removal if treatment must be halted early.
  • Clinical studies use higher doses than the 1972 label. The label suggests 150–450 mg (2–6 pellets) every 3 to 6 months, whereas post-2008 studies routinely implanted 600–900 mg (8–12 pellets) and found levels typically drop below 300 ng/dL by 3 to 4 months (100–120 days).
  • Low extrusion and infection rates with modern technique. Compared with 8.5–12% extrusion for older 200 mg pellets, series using 75 mg Testopel pellets and the two-track “V” technique report 0.3–1.1% extrusion and 0.3–1.2% infection, mostly in month 1.
  • Intermediate erythrocytosis risk. Over 3 years, hematocrit exceeded 50% in 35.1% of men on Testopel, compared with 12.8% on daily gels and 66.7% on weekly short-acting injections.
  • Schedule III and banned in sport. Regulated under DEA Schedule III in the US and prohibited at all times by WADA.

Sources

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  25. US Code of Federal Regulations. 21 CFR 1308.13, Schedule III. 21 CFR 1308.13.
  26. World Anti-Doping Agency. 2026 Prohibited List. WADA 2026 Prohibited List.