Short answer: The Cytomel label starts most adults with hypothyroidism at 25 mcg by mouth once daily, raised by 25 mcg every 1 or 2 weeks if needed. The usual maintenance dose is 25 mcg to 75 mcg once daily. Older people and those with heart disease start at 5 mcg and step up by 5 mcg. Children start at 5 mcg, with 5 mcg increases every 3 to 4 days.
This is what the FDA label says. Follow your prescriber. Your prescriber may use a different dose or pace than the label's standard schedule.
What Cytomel is approved for: Cytomel is approved as replacement therapy for hypothyroidism from any cause (thyroid, pituitary or hypothalamic, present at birth or acquired), as an add-on to surgery and radioiodine in well-differentiated thyroid cancer, and as a diagnostic drug in thyroid suppression tests. It is not approved to suppress benign thyroid nodules or nontoxic goiter in people with enough iodine, or for hypothyroidism during recovery from subacute thyroiditis (section 1).
Source
CYTOMEL (liothyronine sodium) tablets, for oral use, prescribing information. Pfizer. DailyMed, version published May 21, 2026. DailyMed setid 51452b31-ff68-4e0c-b982-c15502ebf1d3
Cytomel tablets are taken by mouth once daily (section 2.1).
The dose is set for each person based on age, body weight, heart health, other conditions including pregnancy, other medicines, food taken with it and the condition being treated, and is adjusted from regular checkups and lab tests (section 2.1).
The table below is the label's schedule, from the Dosage and Administration section. Numbers are copied exactly; the section is in brackets.
| Use or group | Starting dose | Increases | Usual or target dose |
|---|---|---|---|
| Hypothyroidism, adults | 25 mcg once daily | 25 mcg daily every 1 or 2 weeks, if needed | 25 mcg to 75 mcg once daily |
| Hypothyroidism, elderly or underlying cardiac disease | 5 mcg once daily | 5 mcg increments at the recommended intervals | Not stated |
| Hypothyroidism, pediatric patients | 5 mcg once daily | 5 mcg every 3 to 4 days until the desired response | Infants a few months old may need 20 mcg once daily; at 1 year, 50 mcg once daily may be required; above 3 years, the full adult dose may be necessary |
| Thyroid suppression test | 75 mcg to 100 mcg daily | None; given for 7 days | Radioiodine uptake measured before and after the 7 days |
Newborns (0 to 3 months) at risk of heart failure: the label says to consider a lower starting dose and increase as needed based on clinical and lab response.
Children at risk of hyperactivity start at one-fourth of the full replacement dose and add one-fourth each week until the full dose is reached.
Pregnancy: dose needs may rise. TSH and free-T4 are measured once pregnancy is confirmed and at least each trimester. If TSH is above the trimester range, the dose is raised and TSH checked every 4 weeks; after delivery the dose goes back to the pre-pregnancy level, with TSH checked 4 to 8 weeks postpartum.
For pituitary or hypothalamic hypothyroidism, TSH is not a reliable guide, so serum T3 is used to monitor therapy and kept in the normal range (sections 2.2 and 2.6).
For TSH suppression in thyroid cancer, the dose targets the desired TSH range and may need to be higher.
In the suppression test, a 50% or greater drop in radioiodine uptake after 7 days indicates a normal thyroid-pituitary axis.
On a stable dose, adults are rechecked every 6 to 12 months and whenever their health changes. Children 3 and older are checked every 3 to 12 months after the dose is stable, until growth and puberty are complete. In children, TSH failing to fall below 20 IU per liter may mean therapy is not adequate.
If heart symptoms develop or worsen, the label says the dose is reduced or held for one week and restarted at a lower dose.
The Cytomel label gives no missed-dose instruction. Ask your prescriber or pharmacist what to do if a dose is missed.
When switching from levothyroxine, levothyroxine is stopped and Cytomel is started at a low dose, then raised gradually by response. Cytomel acts quickly, and effects of the previous thyroid medicine may persist for the first several weeks.
In Dose Track you set up Cytomel as a protocol with the dose and schedule your prescriber gave you. A protocol can hold dose steps, each with its own dose and length in days or weeks, so a step-up plan like the one on the label can be entered once and the app moves to the next step on its own. Reminders follow the schedule, and every dose is logged with the date and time, so you can see which step you are on and when your last dose was. The app follows what you enter; it does not choose or change a dose.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.