Detailed definition
Levothyroxine (Synthroid, Levoxyl, Tirosint, generic) is synthetic levo-thyroxine identical to endogenous T4. It is dosed once daily, ideally on an empty stomach with a consistent gap from meals, supplements (especially calcium and iron), and PPIs (which reduce absorption). Typical replacement doses for primary hypothyroidism are 1.6 mcg/kg lean body weight per day, with starting doses lower in older adults or those with cardiovascular disease. TSH is checked 6–8 weeks after dose changes and adjusted to keep TSH in the desired range. Brand-to-generic switching can produce small variations in absorbed dose, so consistency in product is preferred. Combination T4/T3 therapy is sometimes used in patients who feel suboptimal on T4 alone, although the evidence is mixed.
Why it matters in menopause
For midlife women with hypothyroidism that has been undertreated for years, getting TSH into an optimal range can dramatically improve overlapping menopause symptoms (fatigue, brain fog, weight). The two conditions are commonly co-treated.
Related terms
Sources
External references: Wikipedia.