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How long does Cytomel take to start working?

Medically reviewed by Carmen Pope, BPharm. Last updated on May 1, 2025.

Official answer

by Drugs.com

It only takes 4 hours for 95% of a dose of Cytomel to be totally absorbed and Cytomel will start working within a few hours, but it will take 2 to 3 days of taking it daily to reach its maximal pharmacological effect.

  • This is because it takes a while for blood levels of Cytomel to build up in the body and reach steady state (this is when levels of T3 are relatively stable in the body and do not go up and down).

If you are taking Cytomel daily you may notice some reduction in your symptoms of low thyroid levels (hypothyroidism) within a few hours but it may take 2 to 3 days before you notice any real difference. Symptoms of hypothyroidism include tiredness, increased sensitivity to cold, constipation, and dry skin.

What is Cytomel?

Cytomel contains liothyronine in a sodium salt form (also called LT3) which is a man-made form of one of our naturally occurring thyroid hormones, also called liothyronine.

  • Cytomel may be used to increase levels of thyroid hormone in the body and treat hypothyroidism (low thyroid levels).
  • It may also be given to help manage thyroid cancer in addition to surgery and radiotherapy, or to help diagnose conditions such as mild hyperthyroidism (high thyroid levels).
References

Read next

Can I take Cytomel and Synthroid together?

Although the American Thyroid Association guidelines do not recommend taking Cytomel and Synthroid together, many people who are under the supervision of an internist/endocrinologist do take this combination treatment, prefer it, and have good results on it. Never take this combination without your doctor's advice because it may result in excessive levels of thyroid hormones which can be dangerous. Continue reading

Does Cytomel help with weight loss?

Although Cytomel does help with weight loss in people prescribed it for hypothyroidism (low thyroid levels), it is not effective at usual dosages at reducing weight in people with normal thyroid levels. Using high dosages of Cytomel to reduce weight in people with normal thyroid levels is dangerous, not safe, and can be life-threatening. Strokes, seizures, shock, coma and death have been reported in people who have taken higher than recommended dosages of Cytomel. Continue reading

How long does Cytomel stay in your system?

Cytomel stays in your system for approximately 12.5 days following the last dose, but this does not mean has an effect for this length of time. This is just how long it takes for your body to eliminate it, and the likely time it could be detectable on a test, if one were available.

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