Levothyroxine Side Effects

Side Effects

Levothyroxine is a kind of synthetic hormone which can be found in the thyroid glandule. This is used as a medicine for thyroid insufficiency replacement in treating hypothyroidism in which the thyroid hormones are low in amount. In addition, Levothyroxine is used in treating congenital hypothyroidism or cretinism and some types of thyroid cancers.

This can be given to prevent or reduce goiter wherein the thyroid glandule is enlarged. It should not be used for other purposes such as treating obesity or infertility provided that it is not due to low level of thyroid hormones. Usually, levothyroxine is well tolerated and patients can have it over a period of years. However, some people will frequently experience side effects because of overdose. The most prevalent side effect of Levothyroxine is hyperthyroidism which is a syndrome with excessive thyroid hormones.

The symptoms of hyperthyroidism which is medically induced are:

  • Tachycardia or increased heart rate
  • Changes in mood
  • Hyperactivity
  • Anxiety
  • Bad temper
  • Fretfulness
  • Tremors
  • Hot sensation
  • Sweating is increased
  • Flushing
  • Presence of fever
  • Loss of weight even if appetite has increased
  • Weakness of muscles
  • Vomiting
  • Loose bowel movement
  • Cramps in the stomach
  • Breathing can be painful or difficult
  • Blood pressure is high
  • Palpitations of the heart
  • Pain on the chest
  • Difficulty going to sleep
  • Loss of hair
  • Problems with the menstrual cycle
  • Seizures
  • Serious unfavorable effects

    If you happen to experience any of these symptoms, it is best to contact your health provider in order to find out the source and adjust the dosage of Levothyroxine. Extreme side effects:

    Serious unfavorable effects frequently develop because of hyperthyroidism. These include broken bones or femoral fractures in males and other indications of weakened boned because of reduction of bone density, arrhythmias or premature ventricular beats, angina pectoris, myxedema coma, adrenal cortical insufficiency particularly with no treatment of the coexisting adrenal insufficiency, heart arrest, diabetes mellitus, heart attack, hypoglycemia, problems with fertility, heart failure and osteoporosis. In elderly individuals, Levothyroxine will result to increased risk of coronary artery disease.

    Side Effects Which Occur Among Pregnant Women

    During pregnancy, women particularly with hypothyroidism condition must monitor closely their levels of thyroid hormones. Low level can be a problem during the course of pregnancy and will have a negative effect on the baby. But if Levothyroxine is given in adequate doses, this will not affect the fetus. However, if you become pregnant while taking Levothyroxine, it is important to call your doctor in order to make adjustments with the dosage. This is usually increased.

    In infants, overdosage will lead to premature closure of the epiphyses and will result to reduction of the future height in an adult person as well as craniosynostosis. Children who are taking Levothyroxine for hypothyroidism replacement, side effects include slipped capital femoral epiphyses and pseudomotor cerebri.


    It is possible that you might not experience any of these side effects. Your doctor also will not be able to predict the reactions of your body to Levothyroxine until you can try it. This is exactly the reason why you should always inform your doctor in case there is something wrong with your health condition. Thus, if you think something is not right, you need to ask your doctor for advice so that he can make a diagnosis with the problem if it is related with your medicine intake. Also, you have to be careful since several side effects of Levothyroxine need urgent medical help. Emphasis is on etiology of infections ( sepsis , pneumonia and UTI ) and sensitivity of isolated microorganisms .