Resveratrol, a naturally occurring compound found in red grapes, berries, and Japanese knotweed, has gained attention for its potential health effects, including possible influences on blood clotting. Many people wonder whether resveratrol acts as a blood thinner, particularly if they take anticoagulant or antiplatelet medications. Whilst laboratory studies suggest resveratrol may affect platelet function, its clinical significance in humans remains uncertain. In the UK, resveratrol is regulated as a food supplement, not a licensed medicine, and carries no authorised medical claims. Understanding the evidence, potential interactions, and safety considerations is essential before starting supplementation, especially for those on prescribed blood-thinning medications.

What Is Resveratrol and How Does It Work?

Resveratrol is a naturally occurring polyphenolic compound found predominantly in the skins of red grapes, berries, peanuts, and Japanese knotweed (Polygonum cuspidatum, also known as Reynoutria japonica). It belongs to a class of plant compounds called stilbenes, which plants produce as a defence mechanism against environmental stressors such as fungal infection or ultraviolet radiation. In recent decades, resveratrol has attracted considerable scientific interest due to its potential antioxidant and anti-inflammatory properties.

The proposed mechanisms of action for resveratrol are multifaceted and complex. Laboratory and animal studies suggest resveratrol may activate certain proteins called sirtuins, particularly SIRT1, which play a role in cellular metabolism and DNA repair. However, the clinical relevance of these effects in humans remains uncertain. In experimental settings, resveratrol demonstrates antioxidant activity by scavenging free radicals and reducing oxidative stress. Laboratory studies have also suggested that resveratrol may influence various signalling pathways involved in inflammation, cell proliferation, and apoptosis (programmed cell death).

In the UK, resveratrol is regulated as a food supplement, not as a licensed medicine, and has no authorised medical claims. It is typically available in capsule or tablet form, with doses ranging from 50mg to 500mg or higher. It is important to note that whilst resveratrol occurs naturally in foods, the concentrations found in dietary sources are generally much lower than those used in research studies or available in supplements. The bioavailability of resveratrol—the extent to which it is absorbed and utilised by the body—is relatively poor, with rapid metabolism in the gut and liver (primarily through glucuronidation and sulphation) limiting its systemic effects.

Does Resveratrol Thin the Blood?

Resveratrol is not a licensed medicine for anticoagulation or antiplatelet use in the UK and is not recommended by NICE for these purposes. When people ask about 'blood thinners', they typically refer to two types of medications: anticoagulants (which reduce blood clot formation in the circulation) and antiplatelets (which prevent platelets from sticking together). However, laboratory and animal studies have demonstrated that resveratrol may influence certain aspects of blood clotting and platelet function.

Resveratrol has been shown in preclinical research to inhibit platelet aggregation—the process by which platelets clump together to form blood clots. This effect appears to occur through multiple mechanisms, including:

• Inhibition of thromboxane A2 synthesis, a compound that promotes platelet activation

• Reduction in platelet adhesion to blood vessel walls

• Modulation of nitric oxide production, which helps regulate vascular tone and platelet function

• Interference with arachidonic acid metabolism, affecting inflammatory pathways involved in clotting

Whilst these laboratory findings are scientifically interesting, it is crucial to understand that the clinical significance of these effects in humans remains uncertain. Human studies have shown limited and inconsistent antiplatelet effects. The doses used in many research studies far exceed what would typically be consumed through diet or standard supplementation. Furthermore, the poor bioavailability of resveratrol means that blood concentrations achieved through oral supplementation may be insufficient to produce meaningful antiplatelet effects.

That said, the theoretical potential for resveratrol to affect blood clotting means that caution is warranted, particularly for individuals taking prescribed anticoagulant or antiplatelet medications such as warfarin, apixaban, rivaroxaban, edoxaban, dabigatran, clopidogrel, prasugrel, ticagrelor, or aspirin. The combination of resveratrol supplements with these medications could theoretically increase bleeding risk. If you take warfarin, you should consult your healthcare provider and may need closer INR monitoring when starting or stopping resveratrol. For direct oral anticoagulants (DOACs), clinical monitoring rather than blood tests is typically used.

Safety Considerations When Taking Resveratrol

Resveratrol supplements are generally considered well-tolerated when taken at commonly available doses, with most reported adverse effects being mild and gastrointestinal in nature. However, several important safety considerations merit attention, particularly given the lack of comprehensive long-term safety data in humans.

Common adverse effects reported with resveratrol supplementation include:

• Gastrointestinal disturbances (nausea, diarrhoea, abdominal discomfort)

• Headache

• Dizziness

• Fatigue

These effects are typically dose-dependent and may resolve with dose reduction or discontinuation. Most data on side effects come from short-term studies using higher doses.

More concerning is the potential for drug interactions. Beyond the theoretical bleeding risk when combined with anticoagulants, antiplatelets, or non-steroidal anti-inflammatory drugs (NSAIDs), laboratory studies suggest resveratrol may interact with medications metabolised by cytochrome P450 enzymes, particularly CYP3A4, CYP2D6, and CYP2C9. While the clinical significance of these interactions in humans at typical supplement doses is uncertain, they could potentially alter the blood levels of various medications, including certain statins, blood pressure medications, and immunosuppressants. Consult your pharmacist or GP if you take medications with a narrow therapeutic index (e.g., warfarin, tacrolimus, ciclosporin).

Specific populations should exercise particular caution or avoid resveratrol supplementation altogether:

• Pregnant and breastfeeding women: There is insufficient evidence regarding safety in pregnancy and lactation

• Individuals with hormone-sensitive conditions: Resveratrol may have theoretical oestrogenic effects; consult your specialist team before use if you have conditions such as breast cancer, uterine fibroids, or endometriosis

• People scheduled for surgery: Many surgical teams advise stopping herbal supplements 1-2 weeks before elective procedures; consult your surgical team for specific guidance

• Those with bleeding disorders: Conditions such as haemophilia or von Willebrand disease may be exacerbated

It is also worth noting that resveratrol supplements are not subject to the same rigorous regulatory oversight as prescription medications. Quality, purity, and actual resveratrol content can vary considerably between products. Look for supplements from reputable UK manufacturers with batch numbers and quality control information.

If you experience any suspected side effects from resveratrol, report them through the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk) and seek medical advice.

When to Speak to Your GP About Resveratrol

Given the potential for interactions and the lack of definitive clinical guidance, it is advisable to consult your GP or pharmacist before starting resveratrol supplementation, particularly if you have existing health conditions or take regular medications. This conversation becomes especially important in certain circumstances.

You should definitely speak to your GP before taking resveratrol if you:

• Are currently taking anticoagulant medications (warfarin, apixaban, rivaroxaban, edoxaban, dabigatran) or antiplatelet drugs (clopidogrel, prasugrel, ticagrelor, aspirin, dipyridamole)

• Take non-steroidal anti-inflammatory drugs (NSAIDs) regularly, which may increase bleeding risk

• Have a history of bleeding disorders or abnormal bleeding

• Are scheduled for surgery or dental procedures within the next few weeks

• Have been diagnosed with hormone-sensitive cancers or conditions

• Are taking medications for chronic conditions such as diabetes, hypertension, or high cholesterol

• Are pregnant, planning pregnancy, or breastfeeding

• Have liver or kidney disease, as these may affect resveratrol metabolism and clearance

Seek urgent medical attention if you experience any of the following whilst taking resveratrol:

• Unusual or unexplained bruising

• Prolonged bleeding from minor cuts

• Blood in urine or stools (which may appear red, dark, or tarry)

• Severe headaches or visual disturbances

• Unexplained abdominal pain

• Signs of allergic reaction (rash, itching, swelling, difficulty breathing)

For severe bleeding or stroke symptoms, call 999 or 112. For urgent advice, contact NHS 111.

Your GP can review your complete medication list, assess your individual risk factors, and provide personalised advice on whether resveratrol supplementation is appropriate for you. If you take warfarin, your doctor may recommend closer INR monitoring if you start or stop taking resveratrol. Remember that whilst resveratrol is available without prescription, this does not automatically mean it is safe or appropriate for everyone. An informed discussion with a healthcare professional ensures that any supplementation decision is made with full awareness of potential benefits and risks.

Frequently Asked Questions