Medically reviewed by Jessica Swirble, PharmD
Last updated on 3/28/2024

Drug Information | Side Effects | Use & Precautions | Request a Prescription

The use of levothyroxine has been shown to cause side effects in some patients.

Common mild side effects of levothyroxine use include:

• Headache
  
• Fatigue/ tiredness
  
• Weight changes (weight loss or gain)
  
• Diarrhea
  
• Tremors
  
• Nervousness
  
• Sweating
  
• Increased appetite
  
• Hair loss
  
• Joint pain
  
  

More severe side effects include:

• Chest pain or palpitations
  
• Rapid or irregular heartbeat (arrhythmia)
  
• Difficulty breathing
  
• Wheezing
  
• Excessive sweating
  
• Severe mood changes (anxiety, agitation)
  
• Allergic reactions (rash, itching, swelling of the face, lips, or throat)
  
  

Seek medical attention immediately if you experience any severe symptoms while taking levothyroxine. If you experience mild side effects that become severe or do not go away after a few days, speak to a healthcare provider right away.

Tell your healthcare provider about any existing medical conditions, allergies, or other medications you are taking before starting treatment with levothyroxine. This includes prescription drugs, over-the-counter medications, and dietary supplements, as they may interact with this drug.

Tell your provider if you are taking these medications or supplements:

• Antiarrhythmics
  
• Androgens
  
• Antacids
  
• Anticoagulants
  
• Beta-blockers
  
• Cancer medications
  
• Anticonvulsants
  
• Lipid-lowering agents
  
• Corticosteroids
  
• Cough/cold/weight loss medications
  
• Cardiac glycosides
  
• Estrogen-containing medications/ contraceptives
  
• Diuretics
  
• Antidiabetic medications
  
• Antidepressants
  
• Pain medications
  
• Weight loss medications
  
• Antacids/mucosal protectants
  
• Proton pump inhibitors
  
• Antibiotics
  
• Selective serotonin reuptake inhibitors (SSRIs)
  
• Anti-gas agents
  
• Other hormone therapy medications
  
• Tyrosine kinase inhibitors
  
  

You should also mention medical conditions such as:

• Adrenal insufficiency
  
• Diabetes
  
• Atherosclerosis
  
• Bleeding and blood disorders
  
• Pituitary gland disorders
  
• Osteoporosis
  
• Heart disease
  
• Kidney disease
  
• Liver disease
  
  

If you are pregnant, planning to become pregnant, or breastfeeding, consult your healthcare provider before using levothyroxine to assess potential risks and benefits.

Take levothyroxine on an empty stomach, at least 30 minutes to 1 hour before breakfast or as directed by your healthcare provider.

Avoid consuming soybeans, walnuts, or foods high in dietary fiber while taking levothyroxine. Your dosage may need to be adjusted if you consume a high-fiber diet.

Do not eat grapefruit or consume grapefruit juice while taking levothyroxine.

Your healthcare provider will provide specific instructions regarding the use of levothyroxine with food, beverages, and other medications. It's essential to follow their guidance to ensure the effectiveness of the treatment and minimize the risk of side effects.

The symptoms of a levothyroxine overdose include:

• Loss of consciousness
  
• Confusion
  
• Anxiety or nervousness
  
• Slurring speech
  
• Excessive sweating
  
• Cold or clammy skin
  
• Changes in heartbeat or pulse
  
• Insomnia
  
• Shortness of breath
  
• Seizures
  
  

If you experience any of these symptoms, call the poison control helpline at 1-800-222-1222. If an individual has collapsed, is having seizures, or is unresponsive, call 9-1-1 immediately.