Cytomel (Liothyronine) Rebound Effects When Stopping

Is there a documented rebound syndrome after stopping liothyronine?

The Cytomel label's adverse reactions section lists the effects of too much thyroid hormone, such as palpitations, tremor, weight loss and heat intolerance, and does not describe a rebound or withdrawal syndrome [1]. That is not a measurement of what happens after an abrupt stop, so it does not show that stopping is uneventful.

For cardiovascular symptoms that develop or worsen, the label says to reduce or withhold the dose for one week and restart at a lower dose [1].

How quickly T3 acts

Liothyronine is T3 itself, taken as a tablet, rather than T4 that the body has to convert. Normally about 80% of circulating T3 is made from T4 by deiodination in peripheral tissues, and an oral T3 tablet supplies the active hormone directly [1]. The label gives a biological half-life of about 2.5 days, with activity beginning within a few hours and maximum pharmacologic response within 2 or 3 days. It says T4 binds serum proteins more tightly than T3, which partly explains T4's longer half-life [1].

When switching from levothyroxine, the label says Cytomel has a rapid onset and that residual effects of the other preparation may persist for several weeks [1].

What the label says to check around a change in dose

The label directs prescribers to monitor TSH periodically after starting or changing the dose. It notes that total T3 can show the immediate response before TSH has adjusted, and that once a patient is stable, evaluation is every 6 to 12 months. In secondary or tertiary hypothyroidism, TSH is not a reliable measure of dose adequacy and serum T3 is used instead [1].

Stopping is named directly in one place. For people with diabetes, the label says to monitor glycemic control when Cytomel is started, changed or discontinued, because thyroid hormone therapy can worsen glycemic control and increase antidiabetic or insulin requirements [1].

Stopping and the underlying condition

Cytomel is indicated as replacement therapy for primary, secondary and tertiary hypothyroidism [1]. The label calls it a narrow-therapeutic-index drug and says both over- and undertreatment can affect growth, cardiovascular function, bone metabolism, reproductive function, cognition, mood, gastrointestinal function, and glucose and lipid metabolism [1].