Synthroid (levothyroxine): Uses, Dosage & Side Effects

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(Last Updated On: August 30, 2017)

Synthroid is also known as levothyroxine, is a replacement of hormone produced by thyroid gland to regulate the metabolism and body energy. This situation is going to happen when the body doesn’t produce enough hormone on its own.

It is mainly used to treat hypothyroidism (low thyroid hormone), it is used to prevent goitre (enlarged thyroid gland) further causing hormonal imbalance .

Information about Synthroid:

This medication is not to be taken if you have untreated adrenal gland disorder or if have any recent heart attacks. It should be used how the doctor has prescribed and should follow the directions mentioned on the prescription label. It is recommended to not to be used in small or large doses and also not for longer duration than prescribed.

It is not to be used to treat obesity. Dangerous side effects or sometimes death occur on misuse of this drug.

Dosage pattern of Synthroid:

Adult dose:


It is about 1.7mcg/kg/day and older patients may require less than 1mcg/kg/day.

For older patients older than 50yrs :

Initial dose: 25-50mcg/day, and gradually increased at 6-8 weeks as needed

Severe hypothyroidism:

It is about 12.5-25mcg/day with increase of 25mcg/day every 2-4weeks


It is about 10-15mcg/kg/day , a lower starting dosage is considered for infants because high dose more than this may have the risk of cardiac failure.

Infants and children:

It is about initial dose of 25mcg/day and the recommended increment should not exceed 25mcg for every 2-4weeks until the desired effects are achieved.

Synthroid overdose:

The overdose of this drug may be fatal, seek immediate medical emergency if following symptoms are seen in the patient.

Symptoms of overdose:

  • Confusion
  • Loss of consciousness
  • Headache
  • Slurred speech
  • Disorientation
  • Lightheadedness
  • Weak pulse

Synthroid side effects:

Severity: major

  • Crying
  • Diarrhea
  • Fear
  • Feeling of discomfort
  • Hair loss
  • Increased appetite
  • Abdominal pain
  • Feeling unhappy
  • Mental depression
  • Restlessness
  • Nervousness
  • Vomiting
  • Weight gain
  • Muscle weakness
  • Weight loss
  • Trouble getting pregnant
  • Rapid mood swings
  • Redness of the face and hands

Synthroid (levothyroxine):

  • Levoxyl
  • Levothroid
  • Unithroid
  • Tirosint


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