Hormones

LH (Luteinizing Hormone)

The pituitary signal that triggers sex hormone production

Plain English

Luteinizing hormone (LH) is produced by the pituitary gland and serves as the primary trigger for sex hormone production in both sexes. In women, a midcycle LH surge triggers ovulation and stimulates progesterone production. In men, LH acts on testicular cells to drive testosterone synthesis. It is a messenger hormone: what goes wrong upstream in the brain or downstream in the gonads shows up in LH levels.

The Mechanism

LH is part of the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus releases gonadotropin-releasing hormone in pulses, which signals the pituitary to release both LH and FSH (follicle-stimulating hormone). These two gonadotropins then act on the gonads: LH primarily drives testosterone production in the Leydig cells of the testes in men, and triggers the LH surge that causes ovulation in women.

In the menstrual cycle, LH rises gradually in the follicular phase and then surges approximately 24-36 hours before ovulation, the peak that at-home ovulation tests detect. After ovulation, LH supports the corpus luteum in producing progesterone for the second half of the cycle.

In men, LH is released in pulses throughout the day, with the largest pulses occurring during sleep. Each pulse stimulates the testes to produce testosterone, which in turn feeds back to the hypothalamus and pituitary to slow LH release, a self-limiting loop. When testosterone is low due to testicular failure, LH rises as the pituitary signals harder for production that is not coming. When testosterone is low due to hypothalamic or pituitary dysfunction, LH stays low or normal. This pattern is how LH distinguishes primary hypogonadism (testicular failure) from secondary hypogonadism (central signaling failure).

Why It Matters

LH tells you where the testosterone problem is, not just that one exists.

LH is diagnostic: its level relative to testosterone tells you where the problem is, not just that a problem exists. Low testosterone with high LH points to a testicular issue. Low testosterone with low or normal LH points to the brain or pituitary. This distinction determines treatment: the first may require testosterone replacement, while the second may respond to interventions that restore hypothalamic function. For women, LH patterns across the cycle reflect ovulatory health, and elevated LH relative to FSH is a primary diagnostic marker in polycystic ovary syndrome (PCOS).

Common Misconception

Low testosterone is often assumed to originate in the testes, and testosterone replacement therapy is offered without checking LH. But low testosterone with low LH means the pituitary is not sending the signal, and replacing testosterone without addressing that treats the symptom while leaving the central dysfunction in place. LH must be checked alongside testosterone for the result to be interpretable.

Signs It Is Disrupted

Low testosterone symptoms (fatigue, low libido, poor recovery, mood changes) in men alongside a low LH reading
Irregular or absent menstrual cycles in women of reproductive age
Anovulatory cycles detected through flat LH readings on ovulation testing
In women, elevated LH-to-FSH ratio (above 2:1 or 3:1) is a clinical marker for PCOS evaluation
Delayed puberty or growth disruption in adolescents, where LH pulsatility fails to initiate properly

How to Improve It

→

Prioritize sleep. The largest LH pulses occur during sleep; chronic sleep deprivation blunts LH pulsatility and reduces testosterone production in men within days.

→

Reduce chronic stress. HPA axis activation raises cortisol, which suppresses hypothalamic gonadotropin-releasing hormone release and reduces LH pulsatility, the central pathway linking chronic stress to low testosterone.

→

Maintain healthy body weight. Both underweight and significant obesity disrupt LH signaling: underweight suppresses the HPG axis through energy conservation, while obesity elevates estradiol via aromatization and disrupts negative feedback.

→

Resistance training. Strength training acutely raises LH and testosterone in men; regular training supports HPG axis tone over time and is one of the most consistent lifestyle interventions for maintaining testosterone.

→

Investigate with full panel. LH should always be tested alongside FSH, total testosterone, free testosterone, and SHBG for the result to be interpretable; the pattern across all markers locates the dysfunction.

3 Things to Remember

LH is the pituitary signal that drives testosterone production in men and triggers ovulation in women. It is a messenger hormone: high or low LH points to where the hormonal problem originates.

Low testosterone with high LH points to a testicular problem; low testosterone with low LH points to a signaling failure in the brain or pituitary. The distinction changes the treatment.

Sleep is the highest-leverage input for LH pulsatility in men; the largest LH and testosterone pulses occur during sleep and are blunted within days of chronic sleep restriction.

Appears In

→How to Read Your Hormone Panel: Testosterone, SHBG, Estradiol, and DHEA →The Lab Work & Biomarkers Protocol →The Stress & Cortisol Protocol

Protocol

Turn what you've learned into daily practice

Protocol pulls your wearable and nutrition data together into a daily health score, morning brief, and AI coaching. All in one place.

Get started free