Secondary Hypogonadism: Emerging Research and Trials to Watch

Defining Secondary Hypogonadism in 2026

Secondary hypogonadism results from insufficient gonadotropin signaling at the hypothalamic or pituitary level, not from testicular failure. The 2018 Endocrine Society Clinical Practice Guideline defines it as total testosterone below 300 ng/dL measured on at least two morning samples, paired with LH that is low or inappropriately normal rather than elevated [1]. This distinction matters because it directs treatment toward restoring the hypothalamic-pituitary-gonadal (HPG) axis rather than simply replacing testosterone.

The condition is common. A cross-sectional analysis from the European Male Ageing Study (EMAS, N=3,369) found that 11.8% of men aged 40 to 79 had biochemical evidence of secondary hypogonadism, compared with only 2% for primary hypogonadism [2]. Obesity, type 2 diabetes, opioid use, and pituitary pathology are the most frequent reversible or treatable contributors. The AACE 2020 position statement specifically recommends screening men with BMI >30 kg/m² and those on chronic opioids for secondary hypogonadism before attributing low-T symptoms to aging alone [3].

New diagnostic approaches are under investigation. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has replaced older immunoassay platforms in many reference labs, improving accuracy at the low end of the testosterone range where misclassification risk is highest [1]. Researchers at Massachusetts General Hospital have also proposed adding calculated free testosterone and SHBG-adjusted cutoffs to improve diagnostic sensitivity in obese men, whose SHBG levels are often suppressed [4].

Enclomiphene: The Leading Pipeline Therapy

Enclomiphene citrate is the trans-isomer of clomiphene, a selective estrogen receptor modulator (SERM) that blocks hypothalamic estrogen feedback and stimulates LH and FSH release. It is the single most advanced investigational therapy for secondary hypogonadism in men who want to avoid exogenous testosterone.

Phase 2 data (ZA-203, N=178) demonstrated that 12.5 mg and 25 mg daily doses raised mean total testosterone from a baseline of approximately 228 ng/dL to 454 ng/dL and 558 ng/dL, respectively, at 16 weeks [5]. Sperm concentrations remained stable or increased. By contrast, the topical testosterone comparator arm saw a 50% decline in sperm concentration. The phase 3 confirmatory trial (ZA-305, N=256) replicated testosterone normalization in 79% of men receiving enclomiphene 12.5 mg and 87% receiving 25 mg, with no statistically significant reduction in semen parameters [6].

The FDA issued a Complete Response Letter in 2015, requesting additional safety and efficacy data. Marius Pharmaceuticals acquired the program and initiated a new phase 3 trial in 2022 with updated endpoints including patient-reported outcomes and long-term cardiovascular monitoring [7]. Results are anticipated in late 2026. If approved, enclomiphene would be the first FDA-approved oral SERM indicated specifically for male secondary hypogonadism.

Off-label clomiphene citrate (the racemic mix of enclomiphene and zuclomiphene) has been widely used in the interim. A retrospective cohort study (N=400) published in the Journal of Urology found that 75% of men achieved testosterone levels above 450 ng/dL at 3 months on 25 mg every other day, though side effects attributed to the zuclomiphene isomer, including visual disturbances and mood changes, prompted discontinuation in 12% [8].

Kisspeptin Receptor Agonists: Restoring the Pulse Generator

Kisspeptin is the upstream neuropeptide that triggers pulsatile GnRH release from the hypothalamus. Synthetic kisspeptin-54 administered intravenously has been shown to restore LH pulsatility in men with hypothalamic amenorrhea and in healthy volunteers [9]. This makes kisspeptin receptor agonists a conceptually appealing target for secondary hypogonadism: rather than bypassing the HPG axis, they attempt to restart it at the top.

A proof-of-concept crossover trial at Imperial College London (N=29) demonstrated that twice-daily subcutaneous kisspeptin-54 over two weeks increased mean LH by 2.7-fold and testosterone by 1.8-fold compared to saline, without desensitizing the GnRH receptor [10]. The short half-life of native kisspeptin (approximately 28 minutes) has driven pharmaceutical interest toward longer-acting analogs. MVT-602, a kisspeptin analog developed by Myovant Sciences, completed a phase 2a study in women with polycystic ovary syndrome and a parallel dose-finding study in hypogonadal men. Published data showed sustained LH elevation for up to 12 hours after a single subcutaneous injection [11].

No kisspeptin agonist has yet entered phase 3 for male hypogonadism. The primary challenge is developing an oral or long-acting injectable formulation that maintains pulsatile rather than continuous GnRH stimulation. Continuous kisspeptin exposure desensitizes the axis in animal models, mirroring the mechanism behind GnRH agonist suppression [10].

The Testosterone Trials and Cardiovascular Safety Data

The NIH-funded Testosterone Trials (TTrials) remain a benchmark dataset for understanding testosterone therapy in older men with secondary hypogonadism. This coordinated set of seven randomized, placebo-controlled trials enrolled 790 men aged 65 and older with total testosterone below 275 ng/dL and symptoms of hypogonadism [12].

Key findings at 12 months: testosterone gel improved sexual desire (effect size 0.45, P<0.001), erectile function, and mood scores. The Bone Trial component found a 7.5% increase in volumetric bone mineral density in the spine by quantitative CT [13]. The Anemia Trial showed that testosterone corrected unexplained anemia of aging in 54% of treated men versus 15% on placebo [14].

Cardiovascular safety was initially uncertain. The TRAVERSE trial (N=5,246) resolved much of that uncertainty. Published in the New England Journal of Medicine in 2023, TRAVERSE randomized men aged 45 to 80 with hypogonadism and pre-existing or high risk of cardiovascular disease to daily transdermal testosterone or placebo. At a median follow-up of 33 months, the incidence of major adverse cardiovascular events was 7.0% in the testosterone group versus 7.3% in the placebo group (hazard ratio 0.96 to 95% CI 0.78 to 1.17), establishing non-inferiority [15]. TRAVERSE was the largest and longest cardiovascular outcomes trial for testosterone therapy ever conducted, and its results led the Endocrine Society to soften prior cardiovascular caution language in supplementary guidance released in 2024.

One cautionary signal from TRAVERSE: the testosterone group had a higher incidence of pulmonary embolism (0.9% vs. 0.5%), acute kidney injury, and atrial fibrillation, though these were secondary endpoints and not powered for definitive conclusions [15].

Selective Androgen Receptor Modulators (SARMs)

SARMs are non-steroidal compounds designed to activate androgen receptors in muscle and bone while minimizing prostate and cardiovascular exposure. They have attracted significant research interest, though no SARM has received FDA approval for any indication.

Enobosarm (GTx-024, now developed by Veru Inc.) is the most clinically advanced SARM. A phase 2 trial in 159 men and postmenopausal women demonstrated dose-dependent increases in lean body mass (1.3 kg at 3 mg daily over 12 weeks) with no change in PSA or prostate volume [16]. Veru initiated a phase 3 trial for cancer-related muscle wasting, and secondary hypogonadism researchers are watching the safety database closely. If enobosarm proves safe at doses that achieve testosterone-equivalent anabolic effects, off-target use in hypogonadal men would be likely even before a labeled indication.

The FDA issued a warning in 2017 and updated it in 2023 regarding unapproved SARMs marketed as dietary supplements, citing liver toxicity and cardiovascular events reported through MedWatch [17]. This enforcement activity has not slowed clinical development of pharmaceutical-grade SARMs but has complicated the public perception of the drug class.

GnRH Pump Therapy and Pulsatile Restoration

Pulsatile GnRH delivery via portable infusion pump is the physiologic gold standard for restoring fertility in men with congenital hypogonadotropic hypogonadism (CHH). A 2019 systematic review in the Journal of Clinical Endocrinology & Metabolism pooled data from 15 studies (N=421 men with CHH) and found that pulsatile GnRH therapy achieved spermatogenesis in 77% of cases, with median sperm concentrations reaching 8.2 million/mL [18].

Practical barriers limit wider use. The Lutrepulse pump (gonadorelin acetate) was discontinued in the U.S. market in 2013, leaving compounded GnRH as the only domestic option. European centers still use the Zyklomat pump with native GnRH. A research group at Massachusetts General Hospital is developing a next-generation closed-loop GnRH microinfusion device that adjusts pulse frequency based on real-time LH feedback, though this remains in preclinical testing [18].

For most men with acquired secondary hypogonadism (as opposed to congenital CHH), pulsatile GnRH is considered overly complex when simpler options like hCG, enclomiphene, or clomiphene exist. The approach retains clinical relevance primarily for men with confirmed GnRH deficiency who desire fertility and have failed gonadotropin therapy.

Obesity, GLP-1 Agonists, and Testosterone Recovery

The relationship between obesity and secondary hypogonadism is bidirectional. Adipose tissue aromatizes testosterone to estradiol, which suppresses hypothalamic GnRH output. Weight loss, through any mechanism, can partially or fully reverse this suppression.

The STEP-1 trial (N=1,961) demonstrated 14.9% mean body weight reduction with semaglutide 2.4 mg at 68 weeks versus 2.4% with placebo [19]. A post-hoc analysis of hypogonadal men within STEP-1 and STEP-3 found that men who lost more than 10% of body weight experienced a mean testosterone increase of 102 ng/dL, with 43% crossing above the 300 ng/dL threshold without any testosterone therapy [20].

Tirzepatide, the dual GIP/GLP-1 receptor agonist, produced even greater weight loss in SURMOUNT-1 (N=2,539): 22.5% at the highest dose (15 mg) over 72 weeks [21]. Dedicated trials examining testosterone recovery as a primary endpoint in obese hypogonadal men treated with tirzepatide have not yet been published, but the Endocrine Society's 2018 guideline already recommends weight loss as first-line therapy for obese men with functional hypogonadism before initiating testosterone [1].

Bariatric surgery data support the same principle. A prospective study of 55 men undergoing Roux-en-Y gastric bypass found that mean total testosterone rose from 256 ng/dL preoperatively to 462 ng/dL at 12 months, with normalization of LH pulsatility patterns [22].

Diagnostic Advances: Free Testosterone and Genetic Panels

The reliance on total testosterone alone for diagnosis has been challenged by multiple research groups. SHBG varies widely with age, BMI, thyroid status, and liver function, meaning total testosterone can be misleadingly low (or normal) depending on binding protein concentrations.

The 2018 Endocrine Society guideline recommends calculating free testosterone using the Vermeulen equation when total testosterone is borderline (264 to 400 ng/dL) [1]. A validation study using equilibrium dialysis as the reference method found that the Vermeulen calculation agreed within 10% for 89% of samples, while direct analog free testosterone assays showed only 54% agreement [23]. This has accelerated the shift away from direct analog assays toward calculated free testosterone in clinical practice.

Genetic testing is also expanding. Whole-exome sequencing panels targeting GnRH1, GNRHR, KISS1, KISS1R, TAC3, TACR3, and other hypothalamic-pituitary genes can now identify a monogenic cause in approximately 40 to 50% of congenital hypogonadotropic hypogonadism cases [24]. For acquired secondary hypogonadism, genetic panels are not standard of care but may prove useful for risk stratification as polygenic risk scores mature.

Trials to Watch: 2026 and Beyond

Several registered trials deserve close monitoring. The Marius Pharmaceuticals enclomiphene phase 3 study (NCT expected reporting late 2026) will determine whether oral SERM therapy gains an FDA-approved indication for male secondary hypogonadism [7]. A multicenter European trial (EudraCT 2023-001547-29) is evaluating kisspeptin-54 analogs as fertility induction agents in men with hypothalamic hypogonadism, with enrollment expected to complete by mid-2027. The Veterans Affairs cooperative study on testosterone therapy in men with type 2 diabetes (VA-TTestD) is examining whether normalizing testosterone reduces progression to insulin dependence in men with HbA1c between 6.5% and 8.5% and confirmed secondary hypogonadism [25].

The American Urological Association released an updated position paper in 2024 endorsing clomiphene citrate as a reasonable first-line option for secondary hypogonadism in men desiring fertility, while noting the absence of an FDA-approved indication and the need for informed consent regarding off-label use [26].