Many people with thyroid conditions wonder whether it is safe to take coenzyme Q10 (CoQ10) supplements alongside their prescribed thyroid medication. CoQ10 is a naturally occurring compound involved in cellular energy production and is widely available as an over-the-counter food supplement in the UK. Thyroid medications such as levothyroxine, carbimazole, and propylthiouracil are essential treatments for managing thyroid disorders, requiring careful monitoring and adherence. Whilst no direct interactions between CoQ10 and thyroid medicines are documented in standard UK references such as the British National Formulary, the evidence base for concurrent use remains limited. This article examines what is known about taking CoQ10 with thyroid medication, practical considerations, and when to seek medical advice.

What Is CoQ10 and How Does It Work in the Body?

Coenzyme Q10 (CoQ10), also known as ubiquinone, is a naturally occurring compound found in virtually every cell of the human body. It plays a crucial role in cellular energy production within the mitochondria—the powerhouses of our cells—where it participates in the electron transport chain to generate adenosine triphosphate (ATP), the primary energy currency of cells.

Beyond its role in energy metabolism, CoQ10 functions as a potent antioxidant, protecting cell membranes and lipoproteins from oxidative damage caused by free radicals. The body produces CoQ10 naturally, with higher concentrations typically found in organs with high energy demands such as the heart, liver, kidneys, and pancreas. Production appears to decline with age, though individual variation exists.

Dietary sources and supplementation

CoQ10 is present in small amounts in foods including:

• Oily fish (sardines, mackerel)

• Organ meats (liver, kidney)

• Whole grains

• Spinach and broccoli

In the UK, CoQ10 is regulated as a food supplement, not as a licensed medicine. It is available over the counter without prescription. These supplements typically come in two forms: ubiquinone (the oxidised form) and ubiquinol (the reduced, active form). Quality and bioavailability can vary considerably between products.

Whilst CoQ10 supplementation has been studied for various conditions including heart failure, migraine prevention, and statin-related muscle symptoms, evidence for its efficacy varies considerably across different indications. The compound is generally well tolerated, with mild gastrointestinal symptoms being the most commonly reported adverse effects when they do occur.

Common Thyroid Medications Used in the UK

Thyroid disorders affect a significant proportion of the UK population, with hypothyroidism (underactive thyroid) being particularly common. The mainstay of treatment for hypothyroidism is levothyroxine (also known as L-thyroxine or T4), a synthetic form of the thyroid hormone thyroxine. Levothyroxine is prescribed to replace deficient thyroid hormone and restore normal metabolic function. Common brand names in the UK include Eltroxin and various generic formulations. The medication requires careful dose titration based on thyroid function tests (TSH and free T4 levels), typically reviewed every 6–8 weeks initially, then annually once stable, in line with NICE guidance (NG145).

For hyperthyroidism (overactive thyroid), antithyroid medications are commonly prescribed. These include:

• Carbimazole – the most frequently used antithyroid drug in the UK, which works by inhibiting thyroid hormone synthesis

• Propylthiouracil – an alternative agent, particularly used in the first trimester of pregnancy or in cases of carbimazole intolerance

Both antithyroid medications carry important safety warnings. Patients should stop treatment and seek urgent medical attention if they develop fever, sore throat, mouth ulcers, infection (signs of agranulocytosis), or with propylthiouracil specifically, if they experience jaundice, dark urine, severe abdominal pain or itching (signs of liver injury).

Less commonly, some patients may be prescribed liothyronine (synthetic T3), either alone or in combination with levothyroxine, though NICE guidance generally does not recommend routine T3 prescribing due to limited evidence of benefit and significantly higher cost compared to levothyroxine monotherapy.

Monitoring and adherence

All thyroid medications require regular monitoring through blood tests to ensure therapeutic levels are maintained. Patients are typically advised to take levothyroxine on an empty stomach, ideally 30–60 minutes before breakfast, as food and certain substances can interfere with absorption. The MHRA advises maintaining a consistent levothyroxine product where possible, as even switching between different brands or formulations can occasionally affect thyroid control in sensitive individuals.

Can You Take CoQ10 With Thyroid Medication?

No interactions between CoQ10 and thyroid medications are listed in standard UK references such as the British National Formulary (BNF). However, it's important to note that CoQ10 is a food supplement rather than a licensed medicine, and the absence of listed interactions does not definitively confirm there is no risk. The evidence base for concurrent use remains limited, with few robust clinical trials specifically examining the safety and efficacy of CoQ10 supplementation in patients taking thyroid medications.

Many patients with thyroid conditions do take CoQ10 supplements without apparent adverse effects, often for reasons unrelated to their thyroid disorder, such as cardiovascular health or fatigue management. Most of what we know comes from theoretical considerations of the compounds' mechanisms of action and isolated case reports rather than large-scale controlled studies.

Practical considerations

If you are considering taking CoQ10 whilst on thyroid medication, several practical points merit consideration:

• CoQ10 is a fat-soluble supplement, so taking it with food containing some fat may enhance absorption

• There is no known need to separate the timing of CoQ10 from levothyroxine, unlike some other supplements (such as calcium or iron) which should be taken at least 4 hours apart from thyroid medication

• Quality and dosage of CoQ10 supplements vary considerably; typical supplemental doses range from 100–200mg daily, though you may wish to discuss appropriate dosing with your pharmacist or GP

• If you take warfarin, you should discuss CoQ10 with your anticoagulation clinic as additional INR monitoring may be needed (see later section)

Whilst concurrent use appears generally safe based on current knowledge, it remains prudent to inform your GP or endocrinologist about all supplements you are taking, as this allows for comprehensive medication review and appropriate monitoring of your thyroid function.

Potential Interactions Between CoQ10 and Thyroid Medicines

Whilst direct pharmacological interactions between CoQ10 and thyroid medications are not well established in clinical literature, several theoretical considerations warrant discussion. Understanding these potential mechanisms helps patients and healthcare professionals make informed decisions about supplementation.

Metabolic and cellular effects

Both thyroid hormones and CoQ10 influence cellular metabolism and mitochondrial function, though through different mechanisms. Thyroid hormones regulate the basal metabolic rate and increase oxygen consumption in tissues, whilst CoQ10 participates directly in mitochondrial ATP production. Some researchers have hypothesised that CoQ10 supplementation might theoretically support cellular energy production in hypothyroid patients, though there is no robust clinical evidence to confirm this benefit. Conversely, there is no evidence that CoQ10 interferes with the action of levothyroxine at the cellular level.

Absorption considerations

Unlike minerals such as calcium, iron, or magnesium—which can bind to levothyroxine in the gastrointestinal tract and significantly reduce its absorption—no known binding or clinically important absorption interaction has been demonstrated between CoQ10 and levothyroxine. However, data in this area are limited.

Effects on thyroid function tests

There is currently no evidence in standard UK references that CoQ10 supplementation alters thyroid function test results or affects TSH, free T4, or free T3 levels. Patients taking both CoQ10 and thyroid medication should continue to have their thyroid function monitored according to standard protocols, typically annually once stable on treatment. If thyroid control unexpectedly changes after starting CoQ10, inform your clinician and consider pausing the supplement while rechecking thyroid function tests.

Antithyroid medication considerations

For patients taking carbimazole or propylthiouracil for hyperthyroidism, similar principles apply. There are no documented interactions between these antithyroid drugs and CoQ10 supplements in UK prescribing resources. However, as with any supplement, it is important to maintain open communication with your healthcare team about what you are taking.

When to Speak to Your GP About CoQ10 and Thyroid Treatment

Whilst CoQ10 is available without prescription and is generally considered safe, there are several circumstances in which you should discuss supplementation with your GP or endocrinologist, particularly if you have a thyroid condition.

Before starting CoQ10 supplementation

You should speak to your GP before beginning CoQ10 if you:

• Have recently been diagnosed with a thyroid disorder or have had recent changes to your thyroid medication dose

• Are taking anticoagulants such as warfarin (CoQ10 may affect warfarin effectiveness; discuss with your anticoagulation clinic and arrange additional INR monitoring when starting or stopping CoQ10)

• Have diabetes, as CoQ10 may have modest effects on blood glucose levels

• Are pregnant, planning pregnancy, or breastfeeding

• Have a history of low blood pressure, as CoQ10 may have mild hypotensive effects

Monitoring your thyroid condition

Contact your GP if you experience any of the following whilst taking CoQ10 alongside thyroid medication:

• Symptoms suggesting thyroid dysfunction – such as unexplained weight changes, persistent fatigue, palpitations, tremor, heat or cold intolerance, or changes in bowel habit

• Unusual or persistent side effects that might be attributed to either your thyroid medication or the supplement

If taking antithyroid medications (carbimazole or propylthiouracil), seek urgent medical attention if you develop:

• Fever, sore throat, mouth ulcers or signs of infection (possible agranulocytosis with either drug)

• Jaundice, dark urine, severe itching or right-sided abdominal pain (possible liver injury, particularly with propylthiouracil)

Regular medication reviews

It is good practice to inform your GP about all over-the-counter supplements during routine medication reviews. This allows your healthcare team to:

• Maintain an accurate record of everything you are taking

• Identify any potential interactions with newly prescribed medications

• Provide personalised advice based on your complete medical history

• Ensure appropriate monitoring of your thyroid function continues

Remember that whilst CoQ10 supplementation is not contraindicated with thyroid medications, supplements should not replace prescribed thyroid treatment. Never adjust your thyroid medication dose without medical supervision, as this can lead to serious complications. If you feel your current thyroid treatment is not adequately controlling your symptoms, discuss this with your GP rather than self-treating with supplements.

If you experience side effects that you suspect may be related to CoQ10 or your thyroid medication, you can report these through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).

Frequently Asked Questions