Can I take Levothyroxine and Vitamin B12 together?

Why this happens

Levothyroxine is a synthetic thyroid hormone absorbed in the small intestine, while vitamin B12 (cobalamin) is absorbed further down in the ileum with the help of 'intrinsic factor'. They use different pathways for metabolism and excretion.

What you should do

You can safely take both levothyroxine and vitamin B12. However, for the best results, levothyroxine should be taken on an empty stomach, 30 to 60 minutes before breakfast. Vitamin B12 can be taken at the same time or later in the day with food. If your B12 supplement is part of a multivitamin containing calcium or iron, you must wait at least 4 hours after taking your levothyroxine before taking the supplement, as calcium and iron can block thyroid hormone absorption.

Important precautions

Heart conditions (e.g. angina, heart failure)

If you have a heart condition, your dose must be started very low and increased slowly. Contact your doctor immediately if you experience chest pain or palpitations, as levothyroxine increases the workload on your heart.

Interaction with supplements (Calcium/Iron)

Do not take calcium tablets, iron supplements, or multivitamins at the same time as levothyroxine. You must leave a gap of at least 4 hours between these supplements and your levothyroxine to ensure the medicine works.

Diabetes

Levothyroxine can raise blood sugar levels. If you have diabetes, you must monitor your blood glucose more closely when starting or changing your dose, as your diabetes medication may need to be increased.

Food and drink warnings

Alcohol

It is best to avoid or strictly limit alcohol while taking levothyroxine. While there is no direct chemical reaction, alcohol can affect thyroid function and may worsen symptoms like tiredness or mood changes.

It is best to avoid or strictly limit alcohol while taking Vitamin B12. Heavy alcohol consumption can interfere with the body's ability to absorb Vitamin B12 from the gut and can reduce the amount of the vitamin stored in the liver.

Timing of dose and food/drink

Take your levothyroxine on an empty stomach, at least 30 to 60 minutes before breakfast or any caffeine. Food, milk, and coffee prevent the medicine from being absorbed properly.

Caffeine (Coffee/Tea)

Caffeine can significantly reduce the amount of levothyroxine your body absorbs. You should wait at least 30 to 60 minutes after taking your tablet before drinking coffee or tea.

Dairy products (Milk, Yoghurt, Cheese)

Avoid consuming dairy products at the same time as your levothyroxine. Calcium found in dairy can interfere with how your body absorbs the medicine, making it less effective. It is best to wait at least 4 hours between taking levothyroxine and consuming dairy.

Soya products

Soya can interfere with the absorption of levothyroxine. If you regularly eat or drink soya products, your doctor may need to monitor your thyroid levels more closely. Avoid consuming soya at the same time as your dose.

Kelp and Seaweed

These foods are naturally high in iodine. Too much iodine can interfere with your thyroid treatment and make your condition worse.

High-fibre foods

A diet very high in fibre can reduce the absorption of levothyroxine. If you significantly change your fibre intake, inform your doctor as your dose may need adjusting.

Using other medicines

Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.

Disclaimer

This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.