Levothyroxine: Uses, How It Works, Medicines

How does Levothyroxine work?

Levothyroxine is a copy of the body's main thyroid hormone, so taking it each day replaces what the thyroid cannot make and brings the level in the blood back into the normal range. Tissues convert it into the more active form, T3, as the body needs it.

How to take Levothyroxine

Follow the label or your doctor's advice. Levothyroxine is usually taken once a day on an empty stomach, 30 to 60 minutes before breakfast, at the same time each day. The dose is individual and is adjusted using blood tests, so never change it on your own.

Side effects of Levothyroxine

When the dose is right, levothyroxine usually causes few side effects. Most side effects happen when the dose is too high, which is why regular blood tests matter.

Uncommon or mild

• Trouble sleeping
• Headache
• Feeling anxious or nervous
• Sweating or feeling too hot
• Hair loss
• Shaky hands (tremor) or a fast, pounding heartbeat
• Diarrhoea or weight loss without trying

Who should be careful

Levothyroxine replaces a hormone the body needs, so it is usually taken for life, and the dose is set by blood tests. Too much is as much of a problem as too little.

• Heart disease, high blood pressure or an irregular heartbeat: too much thyroid hormone can strain the heart, so the doctor usually starts with a low dose and raises it slowly
• Adrenal gland problems (such as Addison's disease): these must be treated first, because levothyroxine can make them worse
• Diabetes: levothyroxine can change blood sugar, so your diabetes medicine doses may need to be reviewed
• Weak bones (osteoporosis) or being past the menopause: too high a dose can reduce bone strength, so the lowest effective dose is used
• Overactive thyroid: levothyroxine is generally not suitable
• Pregnancy or planning pregnancy: the dose often needs to rise during pregnancy, so tell your doctor early and do not stop the medicine on your own
• Not for weight loss: levothyroxine must not be used to lose weight, because larger doses can cause serious, even life-threatening, harm
• Biotin (vitamin B7) supplements, including those for hair and nails: they can affect thyroid blood test results, so tell the doctor or the lab
• Past allergic reaction to levothyroxine or any ingredient in the tablet

Medicines and things that interact with Levothyroxine

Several common medicines and supplements stop the body absorbing levothyroxine, and a few change how much is needed. Tell your doctor or pharmacist about everything you take.

• Calcium tablets, iron tablets, antacids and sucralfate: they stop levothyroxine being absorbed properly, so they are usually taken several hours apart. Ask your pharmacist what gap to leave
• Medicines that lower stomach acid, such as omeprazole and other proton pump inhibitors: they can reduce how much levothyroxine is absorbed, so your doctor may check your thyroid blood tests
• Cholesterol medicines called bile acid sequestrants (such as colestyramine): they bind levothyroxine in the gut
• Soya products, high-fibre foods, walnuts and grapefruit juice: they can reduce absorption if taken close to the tablet
• Phenobarbital, rifampicin and sertraline: they may increase the dose of levothyroxine needed
• Warfarin and similar blood thinners: levothyroxine can increase their effect, so clotting tests may be needed
• Digoxin, amiodarone, some antidepressants and diabetes medicines: their effect or the dose needed can change when thyroid treatment starts or changes
• Biotin supplements: they can give misleading results in thyroid blood tests

If someone takes too much

Regulatory status in India

Approved for sale in India as a prescription medicine. Levothyroxine is not on the CDSCO list of banned medicines (the section 26A list has no levothyroxine entry), so check the ingredient list and strength on the pack.

Type of medicine

Levothyroxine belongs to this type of medicine.

• Thyroid hormones

Medicines that contain Levothyroxine

These medicines sold in India contain Levothyroxine. They are listed A to Z, not ranked.

• Thyronorm 50 · 50 mcg tablet

What is Levothyroxine used for?

Medicines that contain Levothyroxine are used for these conditions.

• Underactive thyroid (hypothyroidism)

Common questions