LH & FSH on TRT: Understanding Suppression and Why It Matters

Last Updated: OCTOBER 2023

Men with total testosterone below 300 ng/dL experience a 2.4-fold higher cardiovascular mortality risk compared to those with levels above 600 ng/dL, as reported in a comprehensive study published in the Journal of Clinical Endocrinology & Metabolism in 2018. For many, Testosterone Replacement Therapy (TRT) offers a pathway to optimized health, restoring vitality, energy, and cognitive function. However, the mechanism by which TRT works often leads to a specific effect: the suppression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to near-zero levels. Understanding this suppression is critical for anyone considering TRT, especially those concerned with preserving fertility.

The Hypothalamic-Pituitary-Gonadal (HPG) Axis

To grasp why LH and FSH levels drop on TRT, it’s essential to understand the body’s natural hormone production system, known as the Hypothalamic-Pituitary-Gonadal (HPG) axis. This intricate feedback loop ensures that testosterone levels remain balanced.

1. Hypothalamus: Located in the brain, it releases Gonadotropin-Releasing Hormone (GnRH).
2. Pituitary Gland: Stimulated by GnRH, the pituitary gland—also in the brain—produces LH and FSH.
3. Testes: LH travels to the Leydig cells in the testes, signaling them to produce testosterone. FSH, on the other hand, acts on the Sertoli cells within the testes, which are crucial for spermatogenesis (sperm production). FSH also helps maintain testicular size and function.
4. Negative Feedback: When testosterone levels are sufficient, they send a signal back to the hypothalamus and pituitary, instructing them to reduce GnRH, LH, and FSH production. This feedback loop prevents excessive testosterone production.

This delicate balance ensures that the testes produce both testosterone and sperm as needed.

TRT and HPG Axis Suppression: The Fertility Impact

When exogenous testosterone (such as testosterone cypionate or enanthate) is introduced into the body through TRT, the HPG axis perceives these elevated testosterone levels as endogenous production. This triggers a strong negative feedback signal to the hypothalamus and pituitary gland. As a result, the pituitary drastically reduces or completely halts its production of LH and FSH.

For men on standard TRT protocols (e.g., 100–200mg testosterone cypionate or enanthate per week), LH and FSH levels typically drop to below 0.5 IU/L, effectively near zero. This suppression has direct consequences:

• Leydig Cell Inactivity: Without LH stimulation, the Leydig cells in the testes cease or significantly reduce their natural testosterone production.
• Sertoli Cell Inactivity & Impaired Spermatogenesis: Without FSH, the Sertoli cells cannot effectively support sperm maturation. Consequently, sperm production diminishes significantly, often leading to temporary infertility or azoospermia (complete absence of sperm).
• Testicular Atrophy: Reduced activity of both Leydig and Sertoli cells leads to a decrease in testicular size, as the testes are no longer performing their full range of functions.

It is crucial to understand that while TRT effectively replaces deficient testosterone, it does so by overriding the body’s natural production, which includes the fertility-critical functions of LH and FSH.

The Problem with “Normal” Ranges

The traditional lower bound for total testosterone, often cited around 300 ng/dL, is a remnant of outdated medical calibration. This threshold was largely established based on population studies from the 1970s that included a significant number of sick and elderly men, effectively normalizing sub-optimal testosterone levels. For many men, optimal health and symptom resolution occur at levels considerably higher, typically between 700-1000 ng/dL for total testosterone and 15-25 pg/mL for free testosterone on TRT. Relying solely on the outdated 264 ng/dL “normal” range can lead to under-treatment and continued suffering for men who could benefit from TRT.

Strategies for Fertility Preservation on TRT

For men who require TRT but wish to maintain fertility, specific adjunctive therapies can mitigate LH and FSH suppression. These options work by either mimicking the action of LH/FSH or by stimulating the body’s own pituitary to produce them.

Human Chorionic Gonadotropin (HCG)

HCG is a glycoprotein hormone that closely mimics the action of LH in the male body. When administered alongside TRT, HCG binds to LH receptors on the Leydig cells in the testes, stimulating them to produce intratesticular testosterone (ITT). This local testosterone is vital for spermatogenesis and helps maintain testicular size and function.

• Mechanism: Directly stimulates Leydig cells, bypassing the suppressed pituitary LH.
• Benefits: Preserves intratesticular testosterone production, maintains testicular size, and can preserve fertility by supporting spermatogenesis.
• Dosage: Common protocols include 500–1000 IU administered subcutaneously 2–3 times per week, typically alongside testosterone cypionate or enanthate injections. This helps maintain consistent ITT levels and counteracts testicular atrophy.

A systematic review published in Translational Andrology and Urology in 2019, titled “Fertility preservation in hypogonadal men requiring testosterone replacement therapy,” highlighted HCG’s efficacy in maintaining spermatogenesis while on TRT. The authors concluded, “HCG can successfully maintain ITT and preserve spermatogenesis, making it a viable option for men on TRT desiring fertility.”

Enclomiphene Citrate

Enclomiphene is a selective estrogen receptor modulator (SERM). Unlike TRT which introduces exogenous testosterone, enclomiphene works by blocking estrogen’s negative feedback at the hypothalamus and pituitary gland. By doing so, it signals the brain to produce more GnRH, which in turn leads to increased production of LH and FSH by the pituitary.

• Mechanism: Blocks estrogen receptors in the hypothalamus and pituitary, thereby increasing endogenous GnRH, LH, and FSH release. This stimulates the testes to produce natural testosterone and sperm.
• Benefits: Elevates natural testosterone levels, maintains testicular function, and preserves spermatogenesis and fertility without introducing exogenous testosterone. This makes it an alternative to TRT for some men, particularly those with secondary hypogonadism and a desire for fertility.
• Dosage: Typical dosages range from 12.5–25mg daily or every other day.

When considering enclomiphene, it’s important to recognize that while it raises endogenous testosterone, the overall testosterone levels achieved may not always reach the same peaks as exogenous TRT. However, its primary advantage is the preservation of the HPG axis and, consequently, fertility.

Anastrozole and Estrogen Management

While not directly involved in LH/FSH suppression or fertility preservation, anastrozole is an aromatase inhibitor often used in conjunction with TRT. Its role is to manage elevated estradiol (E2) levels, which can occur as testosterone aromatizes into estrogen. High E2 can exacerbate negative feedback on the HPG axis, contributing to LH/FSH suppression, and can also lead to unwanted side effects like gynecomastia or water retention.

For men on TRT, maintaining E2 levels within an optimal range (e.g., 20–40 pg/mL) is crucial for overall well-being. If E2 rises above this range, anastrozole at low doses (e.g., 0.25–0.5mg 2x/week) may be prescribed to bring levels down. However, overuse of anastrozole leading to too low E2 can also cause side effects like joint pain, dry skin, and mood issues. The goal is balance, not complete suppression of E2. For fertility-focused protocols, carefully managing E2 ensures the most favorable environment for the HPG axis or HCG action.

Monitoring Lab Values on Fertility-Preserving Protocols

Regular lab work is paramount to ensure the effectiveness and safety of any TRT protocol, especially when fertility is a concern.

• Total Testosterone: Aim for 700–1000 ng/dL. This indicates the primary goal of TRT is met.
• Free Testosterone: Target 15–25 pg/mL. This reflects the bioavailable testosterone.
• Estradiol (E2): Maintain 20–40 pg/mL. This prevents estrogen-related side effects and optimizes overall hormone balance.
• LH and FSH:
  • On TRT monotherapy, expect LH/FSH to be <0.5 IU/L.
  • With HCG co-administration, LH will still be suppressed, but the HCG directly stimulates the testes. FSH levels might remain low but the presence of ITT helps spermatogenesis.
  • With Enclomiphene, expect elevated LH/FSH (e.g., >3-5 IU/L), signaling pituitary activity.
• **Sperm Analysis (Semen Analysis):