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Euthyrox Side Effects

Generic Name: levothyroxine

Note: This page contains information about the side effects of levothyroxine. Some of the dosage forms included on this document may not apply to the brand name Euthyrox.

Not all side effects for Euthyrox may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to levothyroxine: oral capsule liquid filled, oral tablet

In addition to its needed effects, some unwanted effects may be caused by levothyroxine (the active ingredient contained in Euthyrox). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking levothyroxine:

Less common
  • Chest pain or discomfort
  • decreased urine output
  • difficult or labored breathing
  • difficulty with swallowing
  • dilated neck veins
  • extreme fatigue
  • fainting
  • fast, slow, irregular, pounding, or racing heartbeat or pulse
  • fever
  • heat intolerance
  • hives or welts
  • increased blood pressure
  • increased pulse
  • irregular breathing
  • irritability
  • menstrual changes
  • nausea
  • pain or discomfort in the arms, jaw, back, or neck
  • shortness of breath
  • skin itching, rash, or redness
  • sweating
  • swelling of the eyes, face, lips, throat, or tongue
  • tightness in the chest
  • tremors
  • troubled breathing
  • Blurred or double vision
  • dizziness
  • eye pain
  • lack or slowing of normal growth in children
  • limp or walk favoring one leg
  • pain in the hip or knee
  • seizures
  • severe headache

If any of the following symptoms of overdose occur while taking levothyroxine, get emergency help immediately:

Symptoms of overdose
  • Change in consciousness
  • cold, clammy skin
  • confusion
  • disorientation
  • fast or weak pulse
  • lightheadedness
  • loss of consciousness
  • sudden headache
  • sudden loss of coordination
  • sudden slurring of speech

Some of the side effects that can occur with levothyroxine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

Less common
  • Abdominal or stomach cramps
  • change in appetite
  • crying
  • diarrhea
  • false or unusual sense of well-being
  • fear
  • feeling not well or unhappy
  • feeling of discomfort
  • feeling of warmth
  • feeling things are not real
  • feelings of suspicion and distrust
  • hair loss
  • headache
  • increased appetite
  • mental depression
  • muscle weakness
  • nervousness
  • quick to react or overreact emotionally
  • rapidly changing moods
  • redness of the face, neck, arms, and occasionally, upper chest
  • restlessness
  • trouble getting pregnant
  • trouble sitting still
  • unusual tiredness or weakness
  • vomiting
  • weight gain
  • weight loss

For Healthcare Professionals

Applies to levothyroxine: compounding powder, injectable powder for injection, intravenous powder for injection, oral capsule, oral tablet


Cardiac function was evaluated in twenty patients requiring TSH suppression for either thyroid goiter or following thyroidectomy and radioactive iodine therapy for thyroid cancer and in twenty age- and sex-matched controls. TSH suppression was associated with an increased incidence of premature ventricular beats, an increased left ventricular mass index, and enhanced left ventricular systolic function. The clinical significance of these changes remains to be determined.[Ref]

Frequency not reported: Palpitations, tachycardia, hypertension, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest[Ref]


Frequency not reported: Changes in symptom presentation for diabetes and adrenal cortical insufficiency[Ref]

Nervous system

Frequency not reported: Headache, hyperactivity, insomnia, seizures[Ref]


Frequency not reported: Hair loss, flushing, urticaria, pruritus, skin rash, angioedema[Ref]


A study evaluated the effect of long-term thyroid hormone therapy on bone mineral density in 196 women (mean age, 74.4 years) compared to a control group comprised of 795 women (mean age, 72.1 years). The mean daily thyroxine dose was 1.99 mcg/kg (range, 0.3 to 6.6 mcg/kg) with a mean duration of therapy of 20.4 years (range, less than 1 to 68 years). Women taking daily doses of 1.6 mcg/kg or more had significantly lower bone mineral density levels at the ultradistal radius, midshaft radius, hip, and lumbar spine compared to controls. However, estrogen use appeared to negate the adverse effects of thyroid hormone on bone mineral density.

Higher rates of femur fractures have been found in males (p=0.008) prescribed long-term thyroid hormone therapy as compared to controls in a case-control analysis of 23,183 patients, from the United Kingdom General Practice Research Database, prescribed thyroid hormone.[Ref]

Frequency not reported: Tremors, muscle weakness, muscle cramps, increased risk of osteoporosis[Ref]


Frequency not reported: Diarrhea, vomiting, abdominal cramps[Ref]


Frequency not reported: Menstrual irregularities, impaired fertility[Ref]


Frequency not reported: Serum sickness[Ref]


Frequency not reported: Increased appetite, weight loss[Ref]


Frequency not reported: Autoimmune disorders (e.g., chronic autoimmune thyroiditis)[Ref]


Frequency not reported: Fatigue, heat intolerance, fever, pseudotumor cerebri and slipped capital femoral epiphysis have been reported in children[Ref]


Frequency not reported: Nervousness, anxiety, irritability, emotional lability[Ref]


1. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. Available from: URL:" ([2006]):

2. Petersen K, Bengtason C, Lapidus L, et al "Morbidity, mortality, and quality of life for patients treated with levothyroxine." Arch Intern Med 150 (1990): 2077-81

3. Sheppard MC, Holder R, Franklyn JA "Levothyroxine treatment and occurrence of fracture of the hip." Arch Intern Med 162 (2002): 338-43

4. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical, Abbott Park, IL.

5. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

6. Leese GP, Jung RT, Guthrie C, Waugh N, Browning MC "Morbidity in patients on L-thyroxine: a comparison of those with a normal TSH to those with a suppressed TSH." Clin Endocrinol (Oxf) 37 (1992): 500-3

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