Jatenzo (Oral Testosterone Undecanoate): Pregnancy & Lactation Safety

Why Jatenzo Carries an Absolute Pregnancy Contraindication

Jatenzo is approved exclusively for adult males diagnosed with conditions causing hypogonadism (low or absent testosterone production) [1]. The FDA prescribing information assigns Pregnancy Category X, meaning the drug is proven to cause fetal harm and its risks in pregnancy completely outweigh any conceivable benefit [2]. This is not a relative warning. It is an absolute bar.

Testosterone is a potent androgen. When a pregnant woman is exposed to exogenous androgens during the critical window of sexual differentiation (weeks 8 through 12 of gestation), the female fetus faces irreversible virilization. Animal reproductive toxicology studies using testosterone propionate in rats and rabbits demonstrated dose-dependent masculinization of female offspring, including labioscrotal fusion, clitoromegaly, and abnormal urogenital sinus development [3]. The Endocrine Society's 2018 clinical practice guideline on testosterone therapy explicitly states: "Testosterone therapy is contraindicated in men planning fertility in the near term and in women who are or may become pregnant" [4].

No controlled human trials of testosterone in pregnancy exist because the known teratogenic risk makes such research unethical. The evidence base rests on decades of case reports, animal models, and pharmacokinetic principles confirming placental transfer of steroid hormones [5].

How Jatenzo Works: Mechanism and Pharmacokinetics

Jatenzo delivers testosterone undecanoate (TU) as an oral lipid-based capsule designed for lymphatic absorption. This is different from older oral methyltestosterone formulations. Older oral androgens underwent extensive first-pass hepatic metabolism, which generated hepatotoxic 17-alpha-alkylated metabolites. Jatenzo's TU formulation is absorbed through intestinal lymphatics when taken with a meal containing at least 30% fat, bypassing the portal circulation and reducing liver exposure [6].

Once absorbed, pancreatic and tissue esterases cleave the undecanoate side chain, releasing native testosterone into systemic circulation. The testosterone then binds to androgen receptors in target tissues (muscle, bone, brain, reproductive organs) and undergoes standard metabolism via 5-alpha-reductase to dihydrotestosterone (DHT) and aromatase to estradiol [1].

In the key trial by Swerdloff et al. (N=166), 87% of men receiving TU capsules achieved a mean serum testosterone within the eugonadal range (300 to 1 to 100 ng/dL) at 3 months, with a mean Cavg of 489 ng/dL across the dose-titration cohort [7]. Peak testosterone concentrations occurred approximately 5 hours post-dose. The drug's half-life is roughly 10 to 12 hours, supporting the twice-daily dosing regimen.

This pharmacokinetic profile matters for the pregnancy discussion: circulating testosterone from Jatenzo is biochemically identical to endogenous testosterone and freely crosses the placenta via passive diffusion [5].

Fetal Virilization: The Core Risk

The primary danger of androgen exposure during pregnancy is virilization of a female fetus. This phenomenon is well-documented from both exogenous androgen exposure and endogenous causes such as congenital adrenal hyperplasia (CAH).

Prader scoring (grades I through V) classifies the severity of genital ambiguity in 46,XX individuals exposed to excess androgens in utero [8]. At the severe end, complete labioscrotal fusion with a penile urethra makes external genitalia indistinguishable from a male phenotype at birth. Timing of exposure determines severity. Exposure before week 12 produces structural changes (fusion, phallic enlargement). Exposure after week 12 causes clitoromegaly alone, since the labioscrotal folds have already separated by that point [3].

A 2019 systematic review of androgen-exposed pregnancies published in the Journal of Clinical Endocrinology & Metabolism confirmed that even low-dose androgen exposure during the first trimester carried measurable virilization risk, with the highest rates observed in pregnancies where the mother used testosterone-containing topical products without knowing she was pregnant [9]. The review included 48 reported cases of inadvertent maternal androgen exposure, and virilization was documented in 72% of female offspring exposed before gestational week 14.

Male fetuses are not exempt from harm. Supraphysiologic androgen levels during development may disrupt the hypothalamic-pituitary-gonadal (HPG) axis, potentially programming altered reproductive function later in life, though human data on this outcome remain limited to case series [10].

Lactation: Why Jatenzo Is Contraindicated During Breastfeeding

Testosterone is a lipophilic steroid hormone. It transfers into breast milk. The FDA label for Jatenzo states the drug should not be used during breastfeeding, and this recommendation applies to all exogenous testosterone formulations [2].

Endogenous testosterone is present in breast milk at low concentrations (typically 40 to 60 pg/mL in lactating women), reflecting normal female physiology [11]. Exogenous testosterone administration raises circulating levels well beyond this range. In hypogonadal males on Jatenzo, mean serum testosterone reaches 489 ng/dL. A lactating woman exposed to this magnitude of androgen would produce breast milk with substantially elevated testosterone concentrations, posing a direct risk to the nursing infant.

Specific concerns for the breastfed infant include premature virilization (accelerated bone age, early pubic hair development), disruption of the neonatal HPG axis, and potential hepatic effects from sustained androgen ingestion [12]. The American Academy of Pediatrics does not classify testosterone as compatible with breastfeeding [13].

No published pharmacokinetic studies quantify the exact milk-to-plasma ratio for testosterone undecanoate specifically. This absence of data reinforces the precautionary contraindication rather than weakening it. The Endocrine Society's guideline takes the position that the known pharmacology of testosterone makes the risk self-evident without requiring dedicated lactation PK studies [4].

Secondary Exposure: Protecting Household Members

Even when Jatenzo is prescribed correctly to an adult male, secondary transfer to a pregnant or lactating partner is a documented concern with testosterone products.

For topical testosterone (gels, creams, patches), the FDA has issued specific warnings about skin-to-skin transfer causing virilization in women and children [14]. Jatenzo carries a lower secondary transfer risk because it is an oral capsule, not a topical. The drug is swallowed intact and absorbed through the GI tract, so skin-to-skin contact during normal use does not produce transfer.

The residual risk comes from handling crushed or opened capsules. If a pregnant woman breaks or chews a Jatenzo capsule (which patients are instructed not to do regardless), dermal or mucosal absorption of concentrated TU could occur. The prescribing information therefore advises that women who are or may become pregnant should not handle damaged Jatenzo capsules [2].

Clinicians prescribing Jatenzo to male patients should ask about household members. If a patient's partner is pregnant or breastfeeding, the conversation should address safe storage, intact-capsule handling, and handwashing after contact with the medication.

What If a Patient Discovers Pregnancy While Their Partner Uses Jatenzo

This scenario is not purely hypothetical. A 2021 pharmacovigilance analysis of the FDA Adverse Event Reporting System (FAERS) identified 156 reports of unintended androgen exposure during pregnancy across all testosterone products between 2004 and 2020 [15]. Most cases involved topical formulations, but oral testosterone products were represented.

The recommended steps are straightforward. The male patient should stop Jatenzo immediately, though the risk of secondary transfer from oral capsules is low compared to gels. The pregnant partner should receive urgent referral to maternal-fetal medicine for anatomic ultrasound evaluation of the fetus. If exposure occurred before gestational week 14, monitoring for genital ambiguity is especially important [9].

Testosterone's half-life means serum levels decline within days of discontinuation. Jatenzo itself clears within approximately 48 to 72 hours. The clinical question is whether exposure already occurred during the sensitive window.

Fertility Considerations for Male Patients on Jatenzo

Exogenous testosterone suppresses the HPG axis through negative feedback on gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH). This suppression causes spermatogenic arrest in most men within 3 to 6 months of starting therapy [4]. Jatenzo is no exception.

A man taking Jatenzo who wishes to conceive with a female partner faces a direct fertility obstacle. Serum testosterone may be normal or high, but intratesticular testosterone (the concentration needed for spermatogenesis) drops precipitously when exogenous androgen shuts down LH-driven Leydig cell production [16].

The Endocrine Society guideline recommends discontinuing all exogenous testosterone at least 3 to 6 months before planned conception and, if needed, substituting human chorionic gonadotropin (hCG) at 1,500 to 3 to 000 IU two to three times weekly to maintain intratesticular testosterone while preserving fertility [4]. Some clinicians add selective estrogen receptor modulators (clomiphene citrate 25 to 50 mg daily) or FSH (75 IU three times weekly) for men with persistent oligospermia after testosterone withdrawal [17].

Recovery of spermatogenesis after testosterone cessation is probable but not guaranteed. A meta-analysis of 30 studies (N=1,549 men) found that 90% of men recovered sperm concentrations above 20 million/mL within 12 months of stopping testosterone, but 10% had prolonged or incomplete recovery [18]. Duration of prior therapy, baseline sperm parameters, and age all influence recovery kinetics.

Contraception Guidance for Couples During Jatenzo Therapy

The dual concern (fetal virilization risk plus male subfertility during therapy) creates a somewhat paradoxical clinical picture. While Jatenzo typically suppresses spermatogenesis, it does not do so reliably enough to serve as contraception. Breakthrough ovulation-equivalent events (residual sperm production) occur in a meaningful minority of men on testosterone [16].

Guidelines therefore recommend that male patients on testosterone therapy whose female partners could become pregnant should use a reliable form of contraception. Barrier methods (condoms), partner-based hormonal contraception, or intrauterine devices are all appropriate options. The conversation should be documented in the medical record [4].

Regulatory and Labeling Context

The FDA approved Jatenzo in March 2019 under NDA 206089 with a Risk Evaluation and Mitigation Strategy (REMS) focused on cardiovascular risk communication, not pregnancy. The pregnancy contraindication is carried forward from the class-wide androgen labeling requirements [2].

Under the Pregnancy and Lactation Labeling Rule (PLLR, effective June 2015), newer drug labels replace the letter-category system (A, B, C, D, X) with narrative subsections describing human data, animal data, and clinical considerations [19]. Jatenzo's label uses both formats: the legacy Category X designation appears alongside narrative text summarizing animal virilization data and the absence of controlled human pregnancy studies.

The European Medicines Agency (EMA) applies similar restrictions to testosterone undecanoate products (marketed as Andriol or Nebido in other formulations), classifying them as contraindicated in pregnancy under EU SmPC requirements [20].