Levothyroxine

What is levothyroxine?

Levothyroxine is a synthetic version of thyroxine (T4). This is a hormone that’s naturally produced by the thyroid gland. It is used to replace or supplement thyroid hormone levels when the body is not producing enough – helping regulate the metabolism, energy production, growth, and other essential bodily functions[2]. 

What is levothyroxine used for?

Doctors prescribe levothyroxine for several thyroid-related conditions. The most common is hypothyroidism (underactive thyroid)[2]. 

How does levothyroxine work?

If your body is missing or not producing the natural thyroxine hormone in sufficient amounts, levothyroxine can replace it. It then plays a critical role in regulating your metabolism, energy levels, temperature, and general development[2]. 

In restoring your hormone balance, levothyroxine helps reverse the symptoms of low thyroid activity. These can include fatigue, weight gain, and depression[2]. 

Who can take levothyroxine?

Levothyroxine is generally safe for adults and children when it’s prescribed under a doctor’s or pharmacist’s supervision. However, it may not be suitable for people with thyrotoxicosis (an overactive thyroid), adrenal gland disorders, or certain heart conditions, such as angina or heart failure[2]. 

It may also not be suitable for individuals with high blood pressure, diabetes, or with a known allergy to levothyroxine or its ingredients.

Please tell your doctor or pharmacist about any conditions you may have before starting fluoxetine, and always follow the instructions in the Patient Information Leaflet[1].

What is the typical dosage of levothyroxine?

A correct dosage of levothyroxine varies. It depends on factors like your age, weight, and the severity of your thyroid deficiency. Your doctor will determine your starting dose and adjust it based on regular blood tests[2]. 

Common levothyroxine dosages range from 12.5mg to 100mg in tablet form, or liquids if swallowing is difficult. Everyone’s unique situation is different, so it’s important never to adjust your dose without medical advice[2]. 

How do you take levothyroxine?

When using levothyroxine, you usually take your tablet once daily, ideally in the morning. It is best taken with water at least 30 minutes before you have breakfast or a drink containing caffeine. Any foods and drinks containing caffeine – such as tea or coffee – can reduce how much of the medication your body absorbs. For that reason, it’s important to leave at least 30 minutes before you take levothyroxine after consumption[2].  

Can you stop taking levothyroxine suddenly?

No, it’s important not to stop taking levothyroxine suddenly unless your doctor or pharmacist advises it. Stopping treatment can cause the return of hypothyroid symptoms. For many people – especially those with permanent thyroid issues – lifelong treatment may be necessary[2]. 

What should you do if you take too much levothyroxine?

Taking more levothyroxine than prescribed can lead to symptoms of hyperthyroidism. These can include a rapid or irregular heartbeat, anxiety or nervousness, sweating, weight loss, along with irritability or restlessness. 

Signs of an overdose can take up to 5 days to appear and may include[1]:  

• Fever 

• Chest pain (angina) 

• Racing or irregular heartbeat 

• Muscle cramps 

• Headache 

• Restlessness 

• Flushing 

• Sweating 

• Diarrhoea 

• Shaking (tremor) 

• Difficulty sleeping (insomnia) 

• Very high temperature (hyperpyrexia). 

If you suspect an overdose, get immediate medical attention – especially if you experience chest pain, confusion, or a racing heart. 

What should you do if you forget a dose of levothyroxine?

If you miss a levothyroxine dose, you can generally take your missed dose as soon as you remember. If your next dose is due soon, skip the missed one – do not take two doses together. 

To help avoid missed doses of levothyroxine, you can try setting a daily reminder or taking it at the same time each morning to build a routine. This often leads to best results[2]. 

Which medicines should you avoid while taking levothyroxine?

The following may affect the way that levothyroxine works[1]: 

• Epilepsy medicines, like carbamazepine, phenytoin, primidone, and barbiturates 

• Sertraline 

• Antacids 

• Medicines containing calcium salts 

• Cimetidine 

• Proton pump inhibitors (such as omeprazole, esomeprazole, pantoprazole, rabeprazole and lansoprazole) 

• Sucralfate 

• Cholestyramine and colestipol 

• Polystyrene sulphone resin 

• Medicines containing iron that are taken by mouth 

• Rifampicin 

• Imatinib 

• Beta blockers such as atenolol and sotalol 

• Oestrogen-containing medicines for hormone replacement therapy (HRT) and contraception (the ‘pill’) 

• Androgen containing medicines for male hormone replacement therapy 

• Corticosteroids such as hydrocortisone and prednisolone 

• Amiodarone 

• Orlistat  

• Ritonavir 

• Products containing St. John’s Wort (an herbal medicinal product) 

The following may be affected by levothyroxine[1]: 

• Anticoagulant medicines like warfarin 

• Diabetes medicines like insulin and metformin 

• Tricyclic antidepressants like amitriptyline, imipramine, and dosulepin 

• Adrenaline or phenylephrine medicine 

• Digoxin 

• Anti-inflammatory medicines like phenylbutazone or aspirin 

• Propranolol 

• Ketamine when used as an anaesthetic, so inform your doctor or anaesthetist that you are taking levothyroxine before an operation. 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[1]. 

What are the side effects of levothyroxine?

With levothyroxine, side effects usually happen due to taking too high a dose. Some of the most common side effects may include nausea, vomiting, diarrhoea, headaches, feeling restless or excitable, sleeping problems, flushing or sweating, muscle cramps and shaking (usually of the hands)[2]. 

In rare cases, serious side effects may include chest pain, shortness of breath, or severe allergic reactions such as rash, swelling, or difficulty breathing. If you experience serious symptoms, call 999[2]. 

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice.

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[1]. 

Frequently asked questions about levothyroxine

How long does levothyroxine take to work? 

Levothyroxine usually starts working soon after your first dose. It may take a few weeks to feel the full effects and for your blood levels to stabilise[2]. 

Can I take levothyroxine during pregnancy? 

Yes, you can usually use levothyroxine during pregnancy. In fact, it's important to maintain proper thyroid hormone levels during pregnancy to support foetal development. Your dose may need to be adjusted, so please speak to your doctor or pharmacist[2]. 

Can I drink alcohol while taking levothyroxine? 

Yes, alcohol in moderation generally does not interfere with levothyroxine. However, excessive alcohol can affect thyroid health, so it’s important to consume it in moderation. If you have side effects like headaches, flushing, or sweating with levothyroxine, alcohol can make them worse[2]. 

Will I need to take levothyroxine for life? 

In many cases, you will need to take levothyroxine for life. This is especially true if your thyroid has been removed or permanently damaged. However, your doctor or pharmacist will advise based on your unique condition[2]. 

Can I take levothyroxine with food? 

It should be taken at least 30 minutes before eating to ensure maximum absorption. You should also leave at least 30 minutes before having a drink containing caffeine, like tea or coffee[2]. 

For the official NHS guide to levothyroxine, visit their website.