Levothyroxine

Levothyroxine is a prescription medication that replaces thyroid hormone in your body. Your thyroid gland normally makes this hormone to control your metabolism, energy levels, and body temperature. When your thyroid does not make enough hormone, a condition called hypothyroidism, you may feel tired, gain weight, or feel cold.

Levothyroxine is a synthetic version of thyroxine, also called T4. This is the main hormone your thyroid produces. The medication works exactly like your natural thyroid hormone. Most people take levothyroxine once daily for the rest of their lives.

Levothyroxine is one of the most commonly prescribed medications in the United States. Millions of people depend on it to feel normal and healthy. Brand names include Synthroid, Levoxyl, and Unithroid, but generic levothyroxine works just as well.

• Hypothyroidism, when your thyroid gland does not produce enough hormone
• Thyroid cancer, to suppress thyroid stimulating hormone after surgery
• Goiter, an enlarged thyroid gland that needs hormone suppression
• Hashimoto's thyroiditis, an autoimmune condition affecting the thyroid
• Thyroid hormone replacement after thyroid removal surgery

Levothyroxine replaces the thyroid hormone T4 that your body is missing. After you swallow the tablet, your digestive system absorbs the medication into your bloodstream. Your body then converts some of the T4 into T3, which is the active form of thyroid hormone. This conversion happens naturally in your liver, kidneys, and other tissues.

The medication tells your cells how fast to work and how much energy to use. It affects nearly every organ in your body. Your heart rate, digestion, muscle function, and brain development all depend on thyroid hormone. When levels are right, you feel normal. When levels are too low, your body slows down. When levels are too high, everything speeds up.

Most adults start with 25 to 50 micrograms per day. Your doctor will adjust your dose based on blood test results. The average maintenance dose is 100 to 125 micrograms daily. Older adults and people with heart disease usually start with lower doses like 12.5 to 25 micrograms. Take levothyroxine on an empty stomach, 30 to 60 minutes before breakfast. Your doctor determines your exact dose based on your TSH levels and symptoms.

• Hair loss during the first few months of treatment
• Headache or mild fatigue as your body adjusts
• Changes in appetite or weight
• Feeling warmer than usual
• Increased sweating
• Temporary insomnia or restlessness

Serious side effects are rare but require immediate medical attention. Call your doctor if you experience chest pain, rapid or irregular heartbeat, shortness of breath, or signs of an allergic reaction. These symptoms may mean your dose is too high. Most side effects happen when your dose needs adjustment.

• Calcium supplements and antacids reduce absorption, take 4 hours apart from levothyroxine
• Iron supplements decrease effectiveness, separate by at least 4 hours
• Estrogen therapy may increase the amount of levothyroxine you need
• Proton pump inhibitors like omeprazole can reduce absorption
• Diabetes medications may need adjustment as thyroid levels normalize
• Blood thinners like warfarin may need dose changes
• Soy products and high-fiber foods can interfere with absorption
• Certain seizure medications can speed up levothyroxine breakdown

Your doctor will check your thyroid stimulating hormone, or TSH, regularly to make sure your dose is right. Most people need blood tests every 6 to 8 weeks when starting treatment or changing doses. Once your levels are stable, you will need testing every 6 to 12 months. Your doctor may also check free T4 and free T3 levels to get a fuller picture of your thyroid function. These tests show whether your body is getting the right amount of hormone.