Levothyroxine: How to Take It Properly, Interactions and Getting the Dose Right

Levothyroxine is one of the most commonly prescribed medicines in the world, and it works well for most people. But small details, like when you take it and what you take it with, can make a big difference to how well it works.

Imagine taking your thyroid tablet with your morning coffee and calcium supplement every day, wondering why you still feel sluggish and your blood tests keep changing. A simple change in timing might be the answer.

What levothyroxine does

Levothyroxine is a man-made version of thyroxine (T4), the main hormone produced by the thyroid gland. It replaces the hormone your body is not making enough of when you have an underactive thyroid (hypothyroidism).,It is also used after thyroid surgery or radioactive iodine treatment, and sometimes in thyroid cancer to suppress TSH. For most people with hypothyroidism, treatment is lifelong.

How to take it

• Take it once a day, at the same time every day
• Take it on an empty stomach with a glass of water, usually 30 to 60 minutes before breakfast or caffeine
• Some people take it at bedtime instead, at least a few hours after their last meal; choose one routine and stick to it
• Swallow tablets whole unless told otherwise

Things that reduce absorption

• Calcium supplements and antacids
• Iron supplements
• Coffee taken at the same time
• Soya products and high-fibre meals close to the dose
• Some medicines for cholesterol (bile acid sequestrants) and stomach acid
• Leave a gap of at least four hours between levothyroxine and calcium or iron

Getting the dose right

Your healthcare provider will start you on a dose based on your age, weight, heart health and how underactive your thyroid is. Older people and those with heart disease usually start on a low dose that is increased slowly.,Blood tests are usually done six to eight weeks after starting or changing the dose, because it takes this long for levels to settle. Once you are stable, tests are often done once a year. The aim is usually to bring TSH into the normal range and relieve symptoms.

Brands and formulations

Different brands and formulations of levothyroxine, including liquids, can vary slightly in how they are absorbed. Some people notice a difference when switched between brands. If you feel different after a change, tell your healthcare provider, who may check your thyroid levels or ask for a consistent brand.

Signs your dose may be too high

• Palpitations or a fast heartbeat
• Feeling anxious, jittery or unable to sleep
• Sweating and feeling hot
• Weight loss
• Diarrhoea
• Long-term over-replacement can thin bones and increase the risk of atrial fibrillation, especially in older adults

Signs your dose may be too low

• Ongoing tiredness
• Feeling cold
• Weight gain
• Constipation
• Low mood
• Dry skin and hair

Pregnancy

Thyroid hormone needs increase in pregnancy. If you take levothyroxine and become pregnant, contact your healthcare provider as soon as possible. Many guidelines advise increasing the dose as soon as pregnancy is confirmed, with blood tests every four to six weeks. Do not stop taking levothyroxine in pregnancy; it is safe and important for you and your baby.

Biotin and thyroid tests

Biotin (vitamin B7), found in some hair, skin and nail supplements, can interfere with some thyroid blood tests and give misleading results. If you take biotin, tell your healthcare provider; you may be asked to stop it for a few days before testing.

Frequently asked questions

What if I miss a dose?

Take it as soon as you remember the same day. If you remember the next day, skip it and take your usual dose. Do not take two doses.

Can I take it with my other morning medicines?

Many can be taken at a different time. Ask your pharmacist about the best timing.

Does levothyroxine cause weight loss?

It treats the weight gain caused by an underactive thyroid, but it should not be used for weight loss.

But I still feel tired even though my results are normal

This is common. Other causes, such as anaemia, low vitamin D, poor sleep or depression, may need checking. Talk to your healthcare provider.

Related: Underactive vs overactive thyroid

Sources: British Thyroid Foundation, American Thyroid Association, National Institute for Health and Care Excellence (NG145), British National Formulary (BNF).