Myths vs facts: FT3 and Müdigkeit

FT3 (free triiodothyronine) is a thyroid hormone often linked to fatigue. A common myth is that low FT3 automatically means hypothyroidism and is the sole cause of exhaustion. In reality, FT3 can be lowered by non-thyroidal illness syndrome (NTIS), calorie restriction, stress, or medications. An isolated low FT3 with normal TSH and FT4 is usually not a sign of treatable hypothyroidism. Another myth: taking T3 supplements (e.g., liothyronine) reliably relieves fatigue. Evidence shows T3 monotherapy in euthyroid individuals with fatigue is no more effective than placebo and carries risks like tachycardia or bone loss. Fact: fatigue has many causes – iron deficiency, sleep disorders, depression, inflammation. FT3 must be interpreted together with TSH, FT4, antibodies, and clinical symptoms. A standalone FT3 test without medical context is misleading. Evidence: strong for thyroid physiology, moderate for fatigue link.