Levothyroxine sodium (Synthroid)

  • Generic name: Levothyroxine sodium (L-thyroxine, T4)
  • Brand names: Levoxyl, Synthroid; Eltroxin, Euthyrox (Canada)
  • Class: Thyroid hormone replacement, Synthetic thyroxine

What is Levothyroxine sodium used for?

  • Hypothyroidism (low thyroid hormone)
  • Goiter (enlarged thyroid gland)
  • Hashimoto’s thyroiditis.

Levothyroxine and pregnancy

Pregnancy Category A.
This means that Levothyroxine is safe to use while you are pregnant. It does not appear to cause any harm to the fetus.

Levothyroxine is suitable for the treatment of hypothyroidism during pregnancy.

Most women on levothyroxine need to increase their dose as soon as they find out that they're pregnant. Usually your doctor will increase your dose by about 25 to 50 micrograms. The exact dose will depend on the results of your blood test.

Levothyroxine and alcohol

There are no known interactions between alcohol and Levothyroxine sodium.

Levothyroxine and coffee

Can you take Levothyroxine with coffee? Several studies have found that drinking coffee at the same or shortly after taking levothyroxine tablets can significantly lower the absorption of the medication3. Wait an hour after taking the levothyroxine before drinking coffee.

Levothyroxine and grapefruit

Grapefruit juice may slightly delay the absorption of levothyroxine.

However, grapefruit appears to have only a minor effect on levothyroxine bioavailability (the amount of drug that reaches your body), according to a 2005 "British Journal of Clinical Pharmacology" study2. To be on the safe side, eat a grapefruit or drink a grapefruit juice several hours after taking your thyroid hormone medicine.

Foods and drugs that decrease Levothyroxine absorption

  • High fiber foods, soybean flour (infant formula), soy protein, cottonseed meal, walnuts
  • Calcium supplements
  • Aluminum-containing antacids
  • Iron sulfate, iron-containing multivitamins
  • Cholestyramine

It is best to take levothyroxine on empty stomach, 30 minutes before breakfast, with a full glass of water.

Levothyroxine contraindications

  • Thyrotoxicosis (when thyroid gland is overactive and produces too much thyroxine)
  • Acute myocardial infarction
  • Uncorrected adrenal insufficiency
  • Hypersensitivity to any of the ingredients


Diabetes: Levothyroxine can increase blood glucose levels, although this is rarely clinically significant. The dose of glucose-lowering drugs may need to be adjusted.

Osteoporosis: Long-term levothyroxine therapy can decrease bone mineral density. Postmenopausal women and women using suppressive doses should receive the lowest dose necessary for clinical response.

Overdosage: Levothyroxine overdosage can result in increased body temperature, tremors, hypoglycemia, fluid loss, tachycardia, and thyroid storm.

Further reading


  • 1. Synthroid prescribing information. PDR. 59th Edition. Montvale, NJ: Thomson PDR, 2005, p. 515.
  • 2. Lilja JJ, Laitinen K, Neuvonen PJ. Effects of grapefruit juice on the absorption of levothyroxine. Br J Clin Pharmacol. 2005 Sep;60(3):337-41. PubMed
  • 3. Benvenga S, Bartolone L, Pappalardo MA, Russo A, Lapa D, Giorgianni G, Saraceno G, Trimarchi F. Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid. 2008 Mar;18(3):293-301.

Last updated: February, 2015

Good to know

Synthroid 50mcg
  • When the thyroid gland is underactive (hypothyroidism) it does not produce enough hormone and metabolism slows. Having enough thyroid hormone is vital for maintaining normal mental and physical activity.
  • Synthroid has been in use since 1955 and was the first oral levothyroxine sodium product.
  • Because not all brands of levothyroxine sodium are equivalent, it is important not to switch between brand names or even between generic formulations.
  • Levothyroxine is ineffective for weight loss in people with normal thyroid function and may cause serious or life-threatening toxicity, especially when taken with amphetamines.