Levothyroxine Side Effects
Not all side effects for levothyroxine 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
Other dosage forms:
In addition to its needed effects, some unwanted effects may be caused by levothyroxine. 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
- fast, slow, irregular, pounding, or racing heartbeat or pulse
- heat intolerance
- hives or welts
- increased blood pressure
- increased pulse
- irregular breathing
- menstrual changes
- pain or discomfort in the arms, jaw, back, or neck
- shortness of breath
- skin itching, rash, or redness
- swelling of the eyes, face, lips, throat, or tongue
- tightness in the chest
- troubled breathing
- Blurred or double vision
- eye pain
- lack or slowing of normal growth in children
- limp or walk favoring one leg
- pain in the hip or knee
- 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
- fast or weak pulse
- 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
- false or unusual sense of well-being
- feeling not well or unhappy
- feeling of discomfort
- feeling of warmth
- feeling things are not real
- feelings of suspicion and distrust
- hair loss
- increased appetite
- mental depression
- muscle weakness
- quick to react or overreact emotionally
- rapidly changing moods
- redness of the face, neck, arms, and occasionally, upper chest
- trouble getting pregnant
- trouble sitting still
- unusual tiredness or weakness
- weight gain
- weight loss
For Healthcare Professionals
Applies to levothyroxine: compounding powder, injectable powder for injection, intravenous powder for injection, oral capsule, oral tablet
Levothyroxine is usually well tolerated. Side effects associated with levothyroxine therapy typically resulted from therapeutic overdosage and included the signs and symptoms of hyperthyroidism. Weight loss, increased appetite, insomnia, anxiety, heat intolerance, diarrhea or increase in bowel frequency, palpitations, hypertension, tachycardia, angina, and menstrual irregularities may be reported. Given the long half-life of levothyroxine, such effects may not be present for several weeks after therapy initiation or dosage increases.
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.
A 38-year-old female experienced with severe hypothyroidism experienced myxedema coma and cardiac ischemia coincident with levothyroxine therapy. After 3 months of levothyroxine therapy (initial dose: 12.5 mcg/d; maintenance dose: 125 mcg/d), all abnormal laboratory values associated with hypothyroidism returned to normal. However, three weeks after initiating treatment, the patient reported intermittent chest pains during the course of treatment, and a coronary artery angiogram revealed diffuse stenosis of all 3 branches. She underwent coronary artery bypass grafting, with subsequent improvement in coronary perfusion.
Cardiovascular side effects have included symptoms of palpitations, hypertension, tachycardia, and angina which may be exacerbated in patients with underlying cardiovascular disorders. Ischemic heart disease and significant effects on cardiac function including an increased incidence of premature ventricular beats, an increased left ventricular mass index, and enhanced left ventricular systolic function have been reported in clinical trials.
Endocrine side effects have included changes in symptom presentation for diabetes and adrenal cortical insufficiency.
Nervous system side effects have rarely included seizures during initiation of therapy.
Dermatologic side effects including transient dermatologic effect and hair loss have been reported during the initial months of therapy.
Musculoskeletal side effects have included an increase risk of osteoporosis. However, data from long-term studies are conflicting.
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.
More about levothyroxine
- Levothyroxine capsules
- Levothyroxine solution
- Levothyroxine (Advanced Reading)
- Levothyroxine Injection (Advanced Reading)
Related treatment guides
Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. Drugs.com does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.