Can I take Levothyroxine and Venlafaxine together?

Why this happens

Levothyroxine is a thyroid hormone replacement, and venlafaxine is an antidepressant (SNRI). They do not interfere with each other's absorption or metabolism in the liver. However, an overactive thyroid (or too much levothyroxine) can increase the risk of heart-related side effects (like a fast heartbeat) which venlafaxine can also cause. Furthermore, untreated hypothyroidism can make depression harder to treat with antidepressants.

What you should do

You can safely take these medicines together. Ensure you take your levothyroxine on an empty stomach, at least 30 to 60 minutes before breakfast or any other medications (including venlafaxine), to ensure it is absorbed properly. It is important to have regular blood tests to ensure your thyroid levels are stable, as this helps your antidepressant work more effectively. If you notice a very fast or irregular heartbeat, palpitations, or increased anxiety, mention this to your doctor.

Important precautions

Mental health worsening

Venlafaxine can cause an increase in suicidal thoughts or self-harm, particularly when first starting treatment or changing doses. Monitor your mood closely and seek urgent medical help if you notice any distressing changes.

Serotonin syndrome

Combining venlafaxine with other medicines that affect serotonin (such as certain painkillers, St John's Wort, or other antidepressants) can cause a life-threatening reaction called serotonin syndrome. Symptoms include high fever, agitation, and muscle twitching.

Bleeding risk

Venlafaxine can increase your risk of bleeding, especially if you are also taking aspirin, ibuprofen, or blood-thinning medicines like warfarin. Seek medical advice if you notice unusual bruising or bleeding.

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 venlafaxine. Combining the two can increase side effects like drowsiness, dizziness, and confusion, and may worsen your underlying condition.

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.