Thyroid hormone is the master regulator of metabolism. Hypothyroidism — underactive thyroid — is dramatically underdiagnosed, and the standard treatment (T4 only) is inadequate for many patients.

The Thyroid System

The thyroid gland produces two hormones:

  • T4 (thyroxine): The storage form; relatively inactive
  • T3 (triiodothyronine): The active form; 3-4 times more potent than T4

T4 must be converted to T3 by deiodinase enzymes in peripheral tissues. Many people have impaired T4-to-T3 conversion, meaning they may have normal T4 levels but inadequate T3 activity.

The Underdiagnosis Problem

Hypothyroidism is dramatically underdiagnosed because:

  1. TSH-only testing: Most physicians test only TSH (thyroid-stimulating hormone), not T3 or T4 directly
  2. Narrow reference ranges: The TSH reference range (0.5-4.5 mIU/L) is based on population averages, not optimal function
  3. Symptom dismissal: Symptoms of hypothyroidism (fatigue, weight gain, cold intolerance, depression) are often attributed to other causes

Many patients with TSH in the "normal" range have symptoms of hypothyroidism and benefit from treatment.

The TSH reference range is based on population averages, not optimal function. Many patients with TSH in the "normal" range have symptoms of hypothyroidism and benefit from treatment.

The T4-Only Treatment Problem

The standard treatment for hypothyroidism is levothyroxine (T4 only). This is inadequate for many patients because:

  • Impaired T4-to-T3 conversion means T4 supplementation does not restore adequate T3 levels
  • T3 is the active hormone; T4 is only useful if converted to T3
  • Multiple studies show that combination T4+T3 therapy improves symptoms and quality of life compared to T4 alone

Natural Desiccated Thyroid

Natural desiccated thyroid (NDT) — derived from porcine thyroid glands — contains both T4 and T3 in the ratio naturally found in thyroid tissue. NDT was the standard treatment for hypothyroidism before synthetic T4 was developed.

Multiple studies and extensive clinical experience suggest that many patients do better on NDT than on synthetic T4 alone. NDT is available as Armour Thyroid, NP Thyroid, and other brands.

Optimal TSH Range

Many thyroid specialists believe the optimal TSH range for symptomatic patients is 0.5-2.0 mIU/L — the lower half of the conventional reference range. Patients with TSH above 2.0 who have symptoms of hypothyroidism may benefit from treatment.