Coenzyme Q10 (CoQ10) is a widely used food supplement valued for its role in cellular energy production and antioxidant properties. Whilst generally well tolerated, some individuals wonder: can CoQ10 cause diarrhoea? The answer is yes—gastrointestinal side effects, including diarrhoea, can occur in some people taking CoQ10 supplements, though these effects are typically mild and uncommon. Understanding why this happens, how to recognise it, and practical strategies to minimise digestive upset can help you use CoQ10 safely and effectively. This article explores the relationship between CoQ10 supplementation and digestive symptoms, drawing on current evidence and UK clinical guidance.

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 an important role in cellular energy production within the mitochondria—the powerhouses of our cells—where it facilitates the conversion of nutrients into adenosine triphosphate (ATP), the primary energy currency used by cells to perform their functions.

CoQ10 exists in two main forms: ubiquinone (the oxidised form) and ubiquinol (the reduced, active antioxidant form). The body can convert between these forms as needed. Beyond energy production, CoQ10 functions as an antioxidant, protecting cell membranes and lipoproteins from oxidative damage caused by free radicals. This dual role makes it particularly important for organs with high energy demands, such as the heart, liver, and kidneys.

The body naturally produces CoQ10, with levels typically peaking in early adulthood and gradually declining with age. Certain medications, particularly statins (cholesterol-lowering drugs), can further reduce CoQ10 levels by inhibiting the same biochemical pathway used to synthesise both cholesterol and CoQ10. However, it's important to note that the National Institute for Health and Care Excellence (NICE) does not recommend routine CoQ10 supplementation for statin-associated muscle symptoms, and patients should not stop taking statins without consulting their GP.

In the UK, CoQ10 is typically sold as a food supplement rather than a licensed medicine. Supplements are available over the counter in various formulations, including capsules, tablets, and liquid preparations. Doses commonly range from 30 to 200 milligrams daily, though higher doses have been used in some studies. As a fat-soluble compound, CoQ10 is best absorbed when taken with meals containing dietary fats. Whilst CoQ10 is generally considered to have a good safety profile, understanding its potential side effects, including gastrointestinal symptoms, is important for anyone considering supplementation.

Can CoQ10 Cause Diarrhoea? Understanding the Side Effects

Yes, CoQ10 can cause diarrhoea in some individuals, though this side effect is relatively uncommon and typically mild when it occurs. Gastrointestinal disturbances, including diarrhoea, are among the more frequently reported side effects, though the exact frequency is difficult to determine due to limited post-marketing surveillance data for food supplements.

Other gastrointestinal side effects that may accompany or occur instead of diarrhoea include:

• Nausea and stomach discomfort

• Loss of appetite

• Abdominal bloating or cramping

• Mild indigestion or heartburn

Beyond the digestive system, CoQ10 has been associated with other generally mild side effects. These include headaches, dizziness, sleep disturbance (consider morning dosing if this occurs), fatigue, skin rashes, and irritability. Serious adverse effects are rare, and CoQ10 has a generally good overall safety profile based on available research.

It is worth noting that the quality and formulation of CoQ10 supplements can vary considerably between manufacturers. Additionally, individual tolerance varies—some people experience no side effects even at higher doses, whilst others may be sensitive to relatively modest amounts.

Important safety information: CoQ10 may reduce the effectiveness of warfarin (an anticoagulant medication). If you take warfarin or other blood-thinning medicines, consult your GP or anticoagulation service before taking CoQ10, as more frequent INR monitoring may be needed. CoQ10 may also enhance the effects of some blood pressure medications.

When to seek medical advice: If diarrhoea persists for more than 7 days, is severe, or is accompanied by blood in the stool, significant abdominal pain, persistent high fever, or signs of dehydration (such as reduced urination, dizziness, or extreme thirst), contact your GP promptly. These symptoms may indicate a more serious condition unrelated to CoQ10 supplementation that requires medical evaluation. If you suspect CoQ10 has caused an adverse reaction, you can report this through the MHRA Yellow Card Scheme.

Why Does CoQ10 Sometimes Cause Digestive Upset?

The mechanisms by which CoQ10 may cause diarrhoea and other gastrointestinal symptoms are not fully understood, but several factors may contribute. As a fat-soluble compound, CoQ10 requires dietary fat for proper absorption in the small intestine. When taken in high doses or without sufficient dietary fat, absorption may be incomplete, potentially contributing to digestive symptoms.

The formulation and bioavailability of different CoQ10 products vary significantly. CoQ10 generally has low and variable oral bioavailability. To improve absorption, manufacturers use various delivery systems, including oil-based suspensions, emulsified formulations, and nanoparticle preparations. Some of these formulations contain excipients, oils, or other ingredients that might affect digestive comfort in some individuals.

Individual factors also play an important role in how supplements are tolerated. People with pre-existing digestive conditions such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), or malabsorption disorders may be more susceptible to gastrointestinal side effects from supplements. Additionally, taking CoQ10 on an empty stomach may increase the likelihood of digestive upset, as does consuming it alongside other supplements or medications that affect gut function.

The timing of supplementation and the overall diet may also influence how well CoQ10 is tolerated. Some people find that taking supplements with certain meals or at specific times of day helps minimise digestive symptoms. Understanding these potential factors can help guide strategies to reduce side effects whilst maintaining the potential benefits of supplementation.

How to Reduce Diarrhoea When Taking CoQ10 Supplements

If you experience diarrhoea or other digestive symptoms when taking CoQ10, several practical strategies can help minimise these effects:

Start with a lower dose and increase gradually: Rather than beginning with the full recommended dose, start with 30–50 mg daily and slowly increase over several weeks. This allows your digestive system to adapt to the supplement and helps identify your personal tolerance threshold.

Take CoQ10 with food: Always consume CoQ10 supplements with meals, particularly those containing some dietary fat (such as nuts, avocado, olive oil, or oily fish). This not only improves absorption but also reduces the likelihood of gastrointestinal irritation.

Divide the daily dose: Instead of taking the entire dose at once, split it into two or three smaller doses throughout the day. For example, if taking 200 mg daily, consider 100 mg with breakfast and 100 mg with dinner. This approach reduces the concentration of CoQ10 in the digestive tract at any given time.

Consider product quality: Some formulations show improved absorption, though differences in tolerability between products are less well established. Choose supplements from reputable manufacturers who can provide evidence of good manufacturing practice (GMP) and quality testing.

Stay well hydrated: Ensure adequate fluid intake throughout the day, particularly if you experience loose stools. This helps prevent dehydration and supports normal digestive function.

Review other medications and supplements: Some medications may interact with CoQ10 or compound digestive side effects. Particularly important is the interaction with warfarin (CoQ10 may reduce its anticoagulant effect) and potentially with blood pressure medications. Discuss your complete medication list with your GP or pharmacist before starting CoQ10.

Consider timing: Taking CoQ10 in the morning or early afternoon may be preferable if you've experienced sleep disturbances.

Special populations: Seek medical advice before taking CoQ10 if you are pregnant, breastfeeding, or considering giving it to children.

If diarrhoea is severe or persists despite these measures, stop taking the supplement and consult your GP. They can assess whether CoQ10 is appropriate for you, recommend alternative approaches, or investigate whether another underlying condition might be contributing to your symptoms. If you suspect an adverse reaction to CoQ10, you can report this through the MHRA Yellow Card Scheme.

Frequently Asked Questions