Oral semaglutide and levothyroxine: taking Wegovy tablets with Eutirox, metformin and alcohol

According to its summary of product characteristics (SmPC), oral semaglutide (Wegovy tablets) increased total exposure to thyroxine by 33% after a dose of levothyroxine. For that reason, the SmPC says monitoring of thyroid parameters should be considered in anyone taking both. There were no clinically relevant changes with metformin, digoxin or furosemide. With warfarin or acenocoumarol, frequent INR monitoring is recommended when treatment starts. Any change to timing or dose is a decision for your doctor or pharmacist.

Wegovy tablets contain oral semaglutide, made by Novo Nordisk, for weight management in adults. In Spain they are available on prescription only. Because the tablet is swallowed on an empty stomach, it clashes with the routine of many people who already take something in the morning. Below is what its SmPC on CIMA, the database of the Spanish Agency of Medicines and Medical Devices (AEMPS), says about each medicine in turn. For the price and the steps to get started, see Wegovy tablets in Spain: price, prescription and how to get started.

Can you take Wegovy tablets with levothyroxine (Eutirox)?

The SmPC does not rule it out, but this is the interaction that needs the most attention. In a study using a single dose of levothyroxine, total exposure to thyroxine (the AUC) rose by 33%, while peak concentration did not change. The SmPC's conclusion is a cautious one: monitoring of thyroid parameters should be considered in anyone taking both. The patient leaflet puts it in plain terms: tell your doctor, pharmacist or nurse if you take levothyroxine, as they may need to check your thyroid levels.

Why does the thyroid matter so much for someone trying to lose weight? Because the right dose of levothyroxine is different for everyone, and too much has noticeable effects. According to the Eutirox SmPC, when someone goes beyond their personal tolerance, symptoms of hyperthyroidism can appear, such as tachycardia, palpitations, tremor, insomnia, sweating, vomiting, diarrhoea or weight loss. Some of these resemble the digestive side effects of Wegovy itself, so it is hard to tell them apart from symptoms alone. That is what blood tests are for. The same SmPC points out that thyroid hormones must not be used for weight loss and that levothyroxine does not reduce weight in people with normal thyroid function.

Then there is the timing. The Eutirox SmPC says to take it in the morning, on an empty stomach, half an hour before breakfast. The Wegovy SmPC says to take the tablet on an empty stomach, ideally after fasting for at least 8 hours, with a sip of water, and then wait 30 minutes before eating, drinking or taking other oral medicines. Both ask for the same window, and neither says which should come first. That decision, along with when to repeat your blood tests, belongs to your doctor or pharmacist, who know your dose. Do not change the timing yourself.

What about metformin?

On the pharmacology, the SmPC is reassuring: there was no clinically relevant change in exposure to metformin when it was taken with semaglutide. What is worth knowing is that the two have similar digestive side effects. The metformin SmPC lists nausea, vomiting, diarrhoea and abdominal pain as very common, especially at the start. The Wegovy SmPC warns that these same symptoms can cause dehydration. The metformin SmPC goes further: if dehydration occurs because of severe vomiting or diarrhoea, metformin should be stopped temporarily and a healthcare professional contacted.

If insulin or a sulphonylurea is also being used, the Wegovy SmPC warns of a higher risk of hypoglycaemia. It allows for the dose of those medicines to be reduced when treatment starts, which only a doctor can adjust. For people whose blood glucose is raised but who do not have diabetes, there is a figure from OASIS 4: among participants with prediabetes, 71.1% returned to normal blood glucose, compared with 33.3% on placebo. We explain what that diagnosis means in what prediabetes is and how it is managed.

What about Sintrom, warfarin and other common medicines?

• Warfarin and acenocoumarol (Sintrom): semaglutide did not cause relevant changes in warfarin or the INR, but there have been reports of a decreased INR with acenocoumarol. The SmPC recommends frequent INR monitoring when treatment starts.
• Rosuvastatin: exposure rose by 41%. The SmPC does not consider this clinically relevant because of rosuvastatin's wide therapeutic margin.
• Digoxin and furosemide: no clinically relevant changes. Omeprazole did not change exposure to semaglutide either.
• Medicines with very low bioavailability (around 1%): interactions have not been evaluated.
• Other GLP-1 receptor agonists: these should not be combined. The patient leaflet names liraglutide, dulaglutide, exenatide and lixisenatide. Use alongside other weight-management products has not been studied either and is not recommended.

Why do the half-hour wait and taking the tablet on its own matter?

The semaglutide tablet is not easily absorbed. According to the SmPC, its bioavailability is around 1–2%. It is absorbed mainly in the stomach with the help of an excipient, salcaprozate sodium, and less is absorbed if it is taken with food or a lot of water. Waiting less than 30 minutes before eating, drinking or taking other oral medicines also reduces absorption.

Other tablets work against it. In a pharmacokinetic trial, taking semaglutide at the same time as five other tablets reduced its exposure by 34% and its peak by 32%. There is also an effect in the opposite direction: semaglutide slows gastric emptying, which could affect the absorption of anything taken by mouth afterwards. The SmPC flags two interactions for monitoring, levothyroxine and coumarin anticoagulants, and both involve medicines whose dose is adjusted based on blood tests. The same rules apply to Rybelsus, the other oral semaglutide. We cover how it differs from Wegovy in Rybelsus or oral Wegovy for weight loss. Talk to your doctor or pharmacist before you move any dose.

Can you drink alcohol while taking Wegovy tablets?

The SmPC and patient leaflet for Wegovy tablets do not mention alcohol or describe any interaction with it. That is not a green light. It means there is no specific rule, so the general precautions for the treatment apply. The first is about timing: after the tablet, nothing to eat or drink for 30 minutes.

The second concerns the pancreas and gallbladder. The SmPC calls for particular caution in people who have had pancreatitis. According to the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), heavy alcohol use and gallstones are among the most common causes of pancreatitis. In OASIS 4, gallstones occurred in 2.5% of people taking the tablet, compared with 1% on placebo.

The third applies to people who also take metformin. Its SmPC names excessive alcohol consumption as a risk factor for lactic acidosis, and the drug is contraindicated in acute alcohol intoxication. The advice from Spain's Ministry of Health (Ministerio de Sanidad) on alcohol applies to everyone: the less, the better. How much you actually drink is something your doctor needs to know to see the full picture.

What does the SmPC say about pregnancy and breastfeeding?

Wegovy tablets should not be used during pregnancy. If you want to become pregnant, treatment is stopped. Because semaglutide has a long half-life of around a week, the SmPC says to stop it at least 2 months before a planned pregnancy. If you become pregnant during treatment, the patient leaflet says to contact your doctor straight away. Wegovy tablets should not be used while breastfeeding either. Semaglutide was not detected in breast milk, but the excipient salcaprozate sodium and some of its metabolites were, and a risk to the baby cannot be ruled out.

How to take the tablet (on an empty stomach, with a little water, and waiting before eating, drinking or taking other medicines) is explained in how to take Wegovy tablets.

Key points

Levothyroxine is the Wegovy tablet interaction that needs the closest monitoring. With metformin there are no relevant changes, though the digestive side effects overlap. With coumarin anticoagulants, the INR needs checking. What you should not do is change the order or dose of your medicines yourself.

What is available in Spain today for medically supported weight loss is medical weight-loss treatment. It starts with an assessment, involves a prescription from a registered doctor where appropriate, and includes ongoing follow-up that takes account of everything you already take. You can:

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