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Levothyroxine Side Effects

Levothyroxine Side Effects

Improper or excessive dosage of levothyroxine may cause some side effects in its users. Here is a brief insight into the adverse effects of this synthetic thyroid hormone.
HealthHearty Staff
Last Updated: Jun 3, 2018
Levothyroxine is a synthetic thyroid hormone that is chemically identical to thyroxine, which is a natural hormone secreted by the thyroid gland. Levothyroxine is used for treating hypothyroidism, goiter, etc. Sometimes, this synthetic hormone is prescribed for those affected with thyroid cancer or nodular thyroid disease. It is available as tablets or capsules for oral consumption, or as intramuscular injections. It is also used as intravenous infusions. The dosage is determined on the basis of factors like age, body weight, medical condition of the user, degree of response to the treatment, and laboratory results. Levothyroxine is found to be safe, but it may cause certain side effects in some users. Such adverse reactions are mostly associated with improper or excessive dosage.
Adverse Effects of Levothyroxine
Levothyroxine may not cause any adverse reaction, if the dosage is aptly tailored to the user's requirement. Tests are conducted at regular intervals, and the dosage is adjusted from time to time, on the basis of test results, so as to avoid long-term side effects of the drug.
Minor Side Effects
Usually, levothyroxine users experience some minor adverse reactions that may subside without any treatment. Such side effects disappear as the body gets adjusted to the treatment. However, you must inform your healthcare provider, who can guide you with some tips to prevent or reduce such side effects, which are given below.
  • Hair loss, headache, weakness
  • Change in appetite, weight loss or weight gain
  • Nervousness, depression, mood swings
These are some of the symptoms experienced by most of the users during the initial days of treatment. However, medical attention must be sought in case the symptoms persist or worsen.
Allergic Reactions
Some people can be allergic to levothyroxine. In that case, they may experience symptoms like difficulty breathing, shortness of breath, swelling of the face and tongue, skin rash, hives, wheezing, flushing, etc. Abdominal pain, nausea, and vomiting may also develop in some cases.
Long-term Overdose Side Effects
Long-term use of levothyroxine in high doses may cause certain side effects that are listed below:
  • Chest pain or discomfort, irregular heartbeats
  • Menstrual changes, impaired fertility
  • Extreme fatigue, sweating
  • Decreased urine output, heat intolerance
  • Insomnia, irritability, hyperactivity
Low mineral density is another condition that may develop in those who are using levothyroxine for a long duration. This condition may lead to osteoporosis.
Massive Overdose Symptoms
  • Lightheadedness, confusion
  • Loss of consciousness
  • Slow or fast pulse rate
  • Cold, clammy skin
  • Difficulty speaking
A massive overdose of levothyroxine may cause life-threatening side effects, and in that case, the user must be provided with immediate medical attention.
Certain foods and drugs may also interact with levothyroxine and cause side effects or affect its efficacy. So, the drug is taken in the morning, on an empty stomach. The user should not take any food for an hour after taking the drug. Food items like soy products, grapefruit juice, etc., may interfere with absorption of the drug. Medication like antacids, and iron and calcium supplements may also affect absorption of levothyroxine in the body.
In short, use of right dosage of levothyroxine is not associated with any major side effect. The drug is often prescribed in individualized doses, which are adjusted according to the clinical and laboratory results. So lab tests are conducted at regular intervals, to monitor the level of thyroid hormones in the body.
Disclaimer: This article is for informational purposes only, and should not be used as a replacement for expert medical advice. Visiting your physician is the safest way to diagnose and treat any health condition.