Levothyroxine overdose in a hypothyroid patient with adjustment disorder: A case report

Levothyroxine (T4) overdose is not frequently encountered and for the clinical signs to materialize, the ingested dose, the rate of conversion of T4 to T3 and chronicity of overdose can be held accountable.

A 29-year-old female, a known case of hypothyroidism and adjustment disorder, under levothyroxine, propranolol and sertraline, intentionally ingested 2.5 mg of levothyroxine but remained asymptomatic with sudden surge in T4 in initial hours of ingestion which gradually started declining along with reciprocal change in TSH. However, the change in T3 was almost negligible.

T3, the active thyroid hormone, when in excess accounts for toxic effects. The duration during physiological process of deiodination and half life of hormone correlates with onset and duration of symptoms. Propranolol which blocks peripheral conversion of T4 to T3 and sertraline which is also reported to reduce the efficacy of levothyroxine, which is evident from low T3 in thyroid profile, must have led to patient being asymptomatic despite lack of early gastric decontamination.

Levothyroxine overdose up to 4mg/day may be asymptomatic but in patients with concomitant neurotic or psychiatric illness, who intentionally take it, are also put on drugs like sertraline and propranolol, the effects of which on thyroid hormones must be contemplated for possible explanation of being asymptomatic.