Do herbal supplements interfere with my blood pressure?
Many people in the UK turn to herbal supplements as a ‘natural’ way to support their health. However, ‘natural’ does not always mean ‘safe,’ especially when managing a chronic condition like high blood pressure. Some herbs contain active compounds that can directly increase your blood pressure or prevent your prescribed medications from working correctly. Understanding these interactions is vital for maintaining cardiovascular stability and preventing avoidable health complications.
What We’ll Discuss in This Article
- Common herbal supplements that can raise blood pressure.
- Herbs that may dangerously lower blood pressure when combined with medication.
- How herbal products can interfere with the metabolism of prescription drugs.
- The causes behind supplement related blood pressure fluctuations.
- Clinical triggers that make herbal interactions more likely.
- Differentiation between regulated medicines and herbal supplements.
Herbs That Can Raise Blood Pressure
Several herbal supplements are known to increase blood pressure or interfere with antihypertensive medications. The most notable is liquorice root, which can cause the body to retain salt and water while losing potassium. Other supplements, such as St John’s Wort, do not necessarily raise blood pressure themselves but can speed up how the body breaks down medications, making your blood pressure pills less effective.
Common herbs to watch for if you have high blood pressure include:
- Liquorice Root: Found in some teas and supplements, it can lead to significant blood pressure spikes and low potassium.
- St John’s Wort: A popular remedy for low mood that is notorious for interacting with a wide range of cardiovascular drugs.
- Ginseng: Some studies suggest it may interfere with blood pressure stability in certain individuals.
- Arnica: While often used topically, oral forms can raise blood pressure and should be avoided by those with hypertension.
- Ephedra (Ma Huang): This is banned in many countries but may still be found in unregulated online supplements; it is a potent stimulant that significantly raises heart rate and blood pressure.
Herbs That Can Lower Blood Pressure Dangerously
Some herbal supplements have a blood pressure lowering effect that can become dangerous when combined with prescription antihypertensives. This can lead to hypotension (excessively low blood pressure), causing symptoms like dizziness, fainting, or falls. Herbs such as garlic, flaxseed, and hawthorn are often cited for their heart benefits, but they must be managed carefully alongside medical treatment.
If you are already taking medication like Ramipril or Amlodipine, be cautious with:
- Garlic: High doses of garlic supplements can have a mild thinning effect on the blood and lower pressure.
- Hawthorn: Frequently used in traditional medicine for heart failure, it can significantly enhance the effect of blood pressure drugs.
- Omega 3 Fatty Acids: While beneficial, very high doses can have a cumulative effect on blood pressure reduction.
- Cat’s Claw: This may lower blood pressure and should be monitored if taken with prescription tablets.
Causes of Herbal Interactions
The primary cause of herbal interference is the way the body processes chemicals in the liver, specifically through the cytochrome P450 enzyme system. Many herbs, such as St John’s Wort, ‘induce’ or speed up these enzymes, causing the body to clear blood pressure medication much faster than intended. This leaves the patient unprotected, even if they are taking their pills regularly.
Other biological causes include:
- Fluid Balance Alteration: Some herbs act as natural diuretics or cause sodium retention, disrupting the delicate balance managed by prescription medications.
- Direct Vasoconstriction: Certain herbal compounds act as stimulants, causing blood vessels to tighten and heart rate to increase.
- Hormonal Interaction: Herbs like liquorice affect the hormone aldosterone, which is responsible for regulating salt and water in the kidneys.
Triggers for Adverse Reactions
The risk of an adverse reaction to a herbal supplement is often triggered by the dose, the duration of use, and your underlying health. Dehydration can trigger more severe side effects when taking herbal diuretics, while a high salt diet can worsen the hypertensive effects of liquorice. Additionally, starting a new supplement at the same time as a new prescription is a common trigger for unstable blood pressure readings.
Clinical triggers to consider:
- Polypharmacy: The more medications you take, the higher the mathematical chance that a herbal supplement will interfere with at least one of them.
- Surgery: Many herbs trigger bleeding risks or blood pressure fluctuations during anaesthesia; surgeons usually require patients to stop all herbal supplements two weeks before an operation.
- Age: Older adults often have reduced kidney or liver function, meaning herbal compounds stay in their system longer and cause more intense interactions.
Differentiation: Regulated vs Unregulated Products
It is important to differentiate between medications with a Marketing Authorisation (PL number) and herbal products, which may have a Traditional Herbal Registration (THR) or no regulation at all. In the UK, a THR mark means the product has been checked for quality and safety, but it does not mean the herb is free from interactions with your other medicines.
- Prescription Medicines: Tested rigorously for interactions, efficacy, and safety.
- THR Herbal Products: Regulated for quality and traditional use; safety information is provided in a leaflet.
- Unregulated Supplements: Often sold online without safety checks; the concentration of active ingredients can vary wildly between bottles.
Conclusion
While herbal supplements are often marketed as ‘natural’ alternatives, they can have a profound impact on your blood pressure and the effectiveness of your medical treatment. Supplements like liquorice and St John’s Wort are particularly risky for those with hypertension. Always consult your GP or a pharmacist before starting any herbal remedy to ensure it will not interfere with your prescribed medications or put your cardiovascular health at risk.
If you experience severe, sudden, or worsening symptoms, such as sudden chest pain, severe dizziness, or a racing heart after taking a supplement, call 999 immediately.
Is it safe to drink liquorice tea if I have high blood pressure?
The NHS advises that people with high blood pressure should avoid eating or drinking too much natural liquorice, as it can cause blood pressure to rise significantly.
Can I take garlic supplements with my blood pressure pills?
You should speak to your doctor first, as high doses of garlic can enhance the effect of your medication and potentially cause your blood pressure to drop too low.
Does St John’s Wort stop blood pressure pills from working?
It can; St John’s Wort increases the speed at which your liver breaks down many medicines, which may result in your blood pressure pills becoming less effective.
Are all ‘natural’ supplements safe for the heart?
No, ‘natural’ does not mean ‘safe.’ Many plants contain powerful chemicals that can affect heart rate, blood pressure, and kidney function.
What is the THR mark on herbal medicine?
The Traditional Herbal Registration (THR) mark shows that a herbal product has been regulated for quality and safety standards in the UK.
Should I tell my surgeon about my herbal supplements?
Yes, you should always inform your surgical team about any supplements you take, as some can interfere with blood pressure and blood clotting during surgery.
Authority Snapshot
This article has been reviewed by Dr. Stefan Petrov, a UK trained physician with an MBBS and extensive experience in general medicine and emergency care. It examines the potential interactions between herbal supplements and blood pressure levels or medications, based on NHS and NICE safety standards. Our goal is to provide evidence based, neutral information to help you understand the risks of self-prescribing herbal remedies while managing hypertension.
