CoQ10 and L-carnitine are naturally occurring compounds that support cellular energy production within the mitochondria. Coenzyme Q10 (CoQ10) functions as an antioxidant and aids ATP synthesis, whilst L-carnitine facilitates fatty acid transport for energy metabolism. Both are synthesised by the body and available through diet, with supplementation increasingly used for cardiovascular health, mitochondrial disorders, and male fertility. In the UK, these are primarily regulated as food supplements rather than licensed medicines. Whilst research suggests potential benefits in specific clinical contexts, evidence quality varies, and supplementation should complement—not replace—conventional medical treatment. Always consult a healthcare professional before starting these supplements, particularly if you have existing health conditions or take prescription medications.

What Are CoQ10 and L-Carnitine?

Coenzyme Q10 (CoQ10) and L-carnitine are naturally occurring compounds that play essential roles in cellular energy production. Both substances are synthesised within the body but can also be obtained through diet and supplementation.

CoQ10, also known as ubiquinone, is a fat-soluble antioxidant found in virtually every cell of the body, with particularly high concentrations in organs with substantial energy demands such as the heart, liver, and kidneys. It functions primarily within the mitochondria—the cellular powerhouses—where it participates in the electron transport chain to generate adenosine triphosphate (ATP), the body's primary energy currency. CoQ10 also provides antioxidant protection by neutralising free radicals and preventing oxidative damage to cellular membranes and DNA. Dietary sources include oily fish (such as mackerel and sardines), organ meats, and to a lesser extent, whole grains and certain vegetables. In the UK, CoQ10 is generally available as a food supplement rather than a licensed medicine.

L-carnitine is an amino acid derivative synthesised from lysine and methionine, predominantly in the liver and kidneys. Its principal function is to transport long-chain fatty acids across the mitochondrial membrane, where they undergo beta-oxidation to produce energy. This makes L-carnitine particularly important for tissues that rely heavily on fatty acid metabolism, including cardiac and skeletal muscle. The body typically produces sufficient L-carnitine for normal physiological function, and it is also present in red meat, poultry, fish, and dairy products. Vegetarians and vegans may have lower dietary intake but generally maintain adequate levels through endogenous synthesis. While most L-carnitine products are food supplements, levocarnitine is available as a licensed medicine in the UK for specific deficiency states, prescribed under specialist supervision.

Both compounds have attracted clinical interest due to their roles in energy metabolism, cardiovascular health, and potential therapeutic applications in various conditions characterised by mitochondrial dysfunction or energy deficiency.

Potential Benefits of Taking CoQ10 and L-Carnitine

The combined use of CoQ10 and L-carnitine has been investigated for several health conditions, though the evidence base varies considerably in quality and consistency.

Cardiovascular health represents one of the most studied areas. CoQ10 supplementation has been examined in heart failure, with some evidence suggesting improvements in symptoms and functional capacity. The Q-SYMBIO study, a randomised controlled trial with 420 participants, demonstrated that CoQ10 supplementation (100 mg three times daily) reduced cardiovascular mortality in patients with moderate to severe heart failure. L-carnitine has similarly been investigated in cardiovascular disease, particularly following myocardial infarction. However, it's important to note that NICE guidelines for heart failure (NG106) and myocardial infarction do not currently recommend routine supplementation with either CoQ10 or L-carnitine, and these agents should not replace evidence-based pharmacological treatments.

Mitochondrial disorders and chronic fatigue have also been areas of interest. Both compounds support mitochondrial function, and there is some evidence that supplementation may benefit individuals with primary mitochondrial diseases. However, the evidence for chronic fatigue syndrome/myalgic encephalomyelitis (ME/CFS) remains limited, and NICE guideline NG206 does not recommend supplements as a treatment for ME/CFS.

Male fertility is another area where both supplements have been studied. Some research suggests that CoQ10 and L-carnitine may improve sperm parameters, including motility and concentration, potentially due to their roles in energy production and antioxidant protection. A systematic review published in the Cochrane Database found some evidence supporting antioxidant supplementation for male subfertility, though improvements in semen parameters do not necessarily translate to increased live birth rates. Men with fertility concerns should seek specialist advice rather than self-medicating.

Statin-related myopathy has prompted interest in CoQ10 supplementation, as statins can reduce endogenous CoQ10 levels. Some patients report reduced muscle symptoms with supplementation, though evidence from randomised controlled trials remains inconsistent. UK guidance does not currently recommend routine CoQ10 supplementation for all statin users.

It is important to emphasise that whilst these supplements show promise in certain contexts, they should not be considered substitutes for conventional medical treatment, and patients should discuss their use with healthcare professionals.

Dosage and How to Take CoQ10 and L-Carnitine

Dosage recommendations for CoQ10 and L-carnitine vary depending on the intended use, though there are no universally established therapeutic doses approved by UK regulatory authorities for most indications.

For CoQ10, typical supplemental doses range from 100 to 300 mg daily, though some clinical trials have used doses up to 600 mg daily for specific cardiovascular conditions. CoQ10 is available in two forms: ubiquinone (the oxidised form) and ubiquinol (the reduced, active form). Some studies suggest ubiquinol may have better absorption in certain populations, particularly older adults, though individual responses vary. As CoQ10 is fat-soluble, absorption is significantly enhanced when taken with meals containing dietary fat. Dividing the daily dose (for example, taking 100 mg twice daily rather than 200 mg once daily) may improve absorption and tolerability.

L-carnitine supplementation typically ranges from 500 mg to 2,000 mg daily, divided into two or three doses. Various forms are available, including L-carnitine tartrate, acetyl-L-carnitine, and propionyl-L-carnitine, each with slightly different pharmacokinetic properties and tissue distribution. Acetyl-L-carnitine, for instance, crosses the blood-brain barrier more readily and has been studied for neurological applications. L-carnitine is water-soluble and can be taken with or without food, though some individuals find that taking it with meals reduces gastrointestinal discomfort.

Licensed levocarnitine (Carnitor) for deficiency states is prescribed under specialist supervision with dosing based on clinical indication and body weight.

Practical considerations include:

• Timing: Some individuals report that taking L-carnitine earlier in the day works better for them, though this is based on anecdotal experience rather than clinical evidence.

• Quality: Choose supplements from reputable manufacturers that adhere to Good Manufacturing Practice (GMP) standards. In the UK, food supplements are regulated under food law rather than medicines regulation. Look for products with third-party testing or quality certifications.

• Duration: Benefits, when they occur, typically require several weeks to months of consistent supplementation.

• Medical supervision: Always inform your GP or specialist about supplement use, particularly if you have existing health conditions or take prescription medications. This is especially important for patients taking warfarin or other anticoagulants, who should consult their anticoagulation clinic before starting or stopping these supplements.

• Dosage safety: Do not exceed the manufacturer's recommended dose unless advised by a healthcare professional.

Patients should be aware that food supplements are not subject to the same rigorous regulatory approval process as medicines, and efficacy claims may not be supported by robust clinical evidence.

Side Effects and Safety Considerations

Both CoQ10 and L-carnitine are generally well-tolerated when used at recommended doses, though certain side effects and safety considerations warrant attention.

CoQ10 side effects are typically mild and may include:

• Gastrointestinal symptoms such as nausea, diarrhoea, or abdominal discomfort

• Headache

• Dizziness

• Insomnia (in some individuals)

• Skin rash (rare)

CoQ10 may interact with warfarin and other anticoagulants, potentially reducing their effectiveness due to its structural similarity to vitamin K. Patients taking anticoagulants should consult their GP or anticoagulation clinic before starting CoQ10 and have their INR monitored more frequently if supplementation begins. Some interactions with antihypertensive medications have been reported, though clinical significance varies.

L-carnitine side effects may include:

• Gastrointestinal disturbances (nausea, vomiting, diarrhoea, abdominal cramps)

• "Fishy" body odour in some individuals

• Restlessness or agitation

• Increased appetite

Seizures have been reported with levocarnitine, particularly with the licensed medicinal form, and caution is advised in individuals with seizure disorders. L-carnitine may also interact with thyroid hormone, potentially interfering with thyroid hormone action, and patients with thyroid conditions should use it cautiously under medical supervision.

Special populations require particular consideration:

• Pregnancy and breastfeeding: There is insufficient evidence regarding safety during pregnancy and lactation. These supplements should be avoided unless specifically recommended by a healthcare professional.

• Children: Paediatric use should only occur under specialist supervision, typically in diagnosed deficiency states or specific metabolic disorders.

• Renal impairment: L-carnitine is renally excreted, and accumulation may occur in kidney disease. Medical supervision is essential.

• Cardiovascular disease: Whilst both supplements have been studied in cardiovascular conditions, they should complement, not replace, evidence-based treatments.

When to seek medical advice:

• Call 999 or go to A&E immediately if you experience chest pain, signs of stroke, severe allergic reaction, or significant bleeding.

• Contact your GP if you experience persistent gastrointestinal symptoms, unusual bleeding or bruising (particularly if taking anticoagulants), seizures, or any other concerning symptoms after starting supplementation.

• Always disclose supplement use before surgery or medical procedures, as some practitioners recommend discontinuation prior to elective surgery.

• Report suspected side effects to the MHRA through the Yellow Card Scheme (yellowcard.mhra.gov.uk).

Frequently Asked Questions