Chronic Fatigue
Also known as: Persistent Fatigue / Hormonal Fatigue
Chronic fatigue — persistent exhaustion that does not improve with rest — affects millions of adults and is one of the most common reasons people seek medical care. While fatigue can have many causes, hormonal deficiencies are among the most frequently overlooked and most effectively treatable. Low testosterone, hypothyroidism, NAD+ decline, cortisol dysregulation, and progesterone deficiency can each cause debilitating fatigue.
In this article
Hormonal Causes of Fatigue
- Low testosterone (men and women): Testosterone directly influences mitochondrial energy production. Low levels mean your cells literally produce less fuel. This manifests as bone-deep exhaustion that caffeine cannot fix.
- Hypothyroidism: Thyroid hormones regulate metabolic rate throughout every cell. Even subclinical hypothyroidism (TSH 2.5-4.5) can cause significant fatigue.
- Low progesterone (women): Disrupted sleep from low progesterone creates a fatigue cascade — poor sleep raises cortisol, which further disrupts sleep.
- Cortisol dysregulation: Both excess and insufficient cortisol cause fatigue. Chronic stress leads to an eventual “burnout” pattern where cortisol output declines.
- NAD+ decline: NAD+ is essential for mitochondrial energy production. Levels drop ~50% between ages 40-60, directly reducing cellular energy output.
- Iron deficiency: Ferritin below 50 ng/mL impairs oxygen delivery, causing fatigue even with normal hemoglobin.
- Vitamin D deficiency: Associated with fatigue, muscle weakness, and depression.
Diagnostic Approach
A comprehensive fatigue workup should include:
- Total and free testosterone
- Thyroid panel (TSH, Free T3, Free T4 — not just TSH alone)
- Cortisol (morning)
- Ferritin (iron stores)
- Vitamin D (25-OH)
- CBC (anemia screening)
- Metabolic panel (kidney, liver, glucose)
- Estradiol and progesterone (women)
- DHEA-S
- Fasting insulin (insulin resistance causes post-meal fatigue)
Key point: If your doctor tests only TSH and CBC and says “everything is normal,” you have not received an adequate evaluation. Most hormonal causes of fatigue require the comprehensive panel above.
Treatment
Treatment targets the specific hormonal cause(s) identified by lab work:
- TRT (men) or HRT (women): Restoring optimal sex hormone levels typically produces noticeable energy improvement within 2-4 weeks.
- Thyroid optimization: Levothyroxine or combination T4/T3 therapy with a target TSH of 0.5-2.0.
- NAD+ therapy: Subcutaneous injections or nasal spray to restore cellular energy production. Many patients notice improved clarity and energy within the first 1-2 weeks.
- Iron supplementation: If ferritin is below 50 ng/mL, supplementation can be transformative.
- Cortisol management: Stress reduction, adaptogens (ashwagandha), sleep optimization.
- Progesterone (women): Restoring progesterone often fixes the sleep disruption that drives daytime fatigue.
Related Conditions
Medical disclaimer: This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read on this website.
Medically reviewed. Last updated: March 2026.