Synthroid Sleep Architecture Impact: What Levothyroxine Does to Your Sleep

What does the label say about sleep?

The label discussed here is the prescribing information for levothyroxine sodium tablets [2]. Insomnia appears in its central nervous system list of reactions that are primarily those of hyperthyroidism from therapeutic overdosage, alongside nervousness, anxiety and irritability [2]. Over-treatment may raise heart rate and cardiac contractility and may precipitate angina or arrhythmias, especially in patients with heart disease and in elderly patients [2].

Is there data on sleep stages?

The sleep-clinic study used polysomnography and follow-up sleep studies, but its reported results do not describe changes in REM or slow-wave sleep [1].

Hypothyroidism, breathing and sleep apnea

In one series, 200 of 290 sequential sleep-clinic referrals judged at high risk for obstructive sleep apnea had polysomnography plus thyroid screening; 124 (62%) had sleep apnea [1]. Three of those 124 patients were newly diagnosed with hypothyroidism, 1.5% of those who had polysomnography; thyroxine alone resolved their symptoms, sleep-disordered breathing, nocturnal hypoxia and thyroid deficiency [1].

Does the time of day you take it matter for sleep?

For levothyroxine sodium tablets, the label says to take one daily dose on an empty stomach, one-half to one hour before breakfast, and at least 4 hours before or after drugs that interfere with absorption [2]. A randomized double-blind crossover trial compared bedtime with morning dosing: of 105 enrolled, 90 completed; bedtime lowered TSH by 1.25 mIU/L more than morning (95% CI, 0.60 to 1.89; P<0.001), raised free T4 by 0.07 ng/dL and total T3 by 6.5 ng/dL [3]. Quality-of-life questionnaires, including a fatigue inventory, showed no significant differences between morning and bedtime intake [3].