The main indication for levothyroxine is treatment of thyroxine deficiency (cretinism, adult hypothyroidism) from any cause. The adult requirement of hormone is remarkably constant, and dosage does not usually have to be altered once the optimum has been found. Patients should be monitored annually. Monitoring needs to be more frequent in children, who may need more as they grow. Similarly, pregnant women should be monitored monthly, and require a 50–100% increase in their normal dose of levothyroxine.
Early treatment of neonatal hypothyroidism (cretinism) (1 in 5000 births) is important if permanent mental defect is to be avoided. It must be lifelong.
Hypothyroidism due to panhypopituitarism requires replacement with glucocorticoids as well as with thyroid hormone. Use of levothyroxine alone can cause acute adrenal insufficiency.
Small doses of levothyroxine in normal subjects merely depress pituitary thyroid-stimulating hormone (TSH) production and consequently reduce the output of thyroid hormone by an equivalent amount.
Levothyroxine is used in some countries for the treatment of non-toxic nodular goitre, on the assumption that nodular thyroid tissue growth is dependent on TSH. The treatment is not curative. Levothyroxine should not be used to treat obesity.
Levothyroxine do not give serious side effects in many people.
- Hair loss – usually temporary
Consult a doctor if you have serious side effects :
- Increased sweating
- Sensitivity to heat
- Mental/mood changes (such as nervousness, mood swings)
- Shaking (tremor)
- Shortness of breath
- Bone pain
- Easily broken bones
Some rare but serious effects of Levothyroxine include:
- Chest pain
- Fast/pounding/irregular heartbeat
- Swelling hands/ankles/feet