Supplements and Medicine Interactions: A Safety Guide

How supplements and medicines interact

• Absorption: minerals such as calcium, iron, magnesium and zinc bind to some medicines in the gut and reduce absorption (thyroid tablets, some antibiotics, osteoporosis tablets). Fibre can bind others.
• Metabolism: some herbs and foods speed up or slow down liver enzymes that break down medicines (St John's wort speeds many; grapefruit slows some), changing blood levels.
• Additive effects: two products doing the same thing, for example two blood-thinning agents, or two blood sugar-lowering agents, add up and can cause bleeding or hypoglycaemia.
• Kidney and liver burden: some supplements and herbs harm these organs, especially when they are already weak.
• Hidden ingredients and contamination: some herbal, Ayurvedic and imported products contain undeclared drugs (steroids, painkillers, diabetes drugs) or heavy metals (lead, mercury, arsenic).
• Duplication: the same vitamin in a multivitamin, a calcium tablet and a "health drink" adds up to excess.

Older adults are at particular risk because of multiple medicines (polypharmacy), reduced kidney and liver function, lower body weight and fewer check-ups; see polypharmacy and deprescribing and medicine side effects families should watch for.

High-risk medicines and the common culprits

### Blood thinners (warfarin, apixaban, rivaroxaban, dabigatran, clopidogrel, aspirin)

• Vitamin K: warfarin works by blocking vitamin K. Large changes in vitamin K intake from multivitamins, green leafy vegetables (methi, palak, coriander leaves, cabbage), green tea, and supplements alter the INR. Keep leafy greens consistent rather than avoiding them, and tell the clinic about changes.
• Supplements that may raise bleeding risk: fish oil at higher doses, vitamin E at high doses, ginkgo, garlic and ginger supplements, turmeric and curcumin, glucosamine, danshen, dong quai, feverfew, and some Ayurvedic products. See omega-3 supplements for seniors: evidence and cautions and joint supplements: what the evidence says.
• St John's wort and some other herbs can reduce the effect of anticoagulants, raising clot risk.
• Alcohol and cranberry products in large amounts alter effects.
• Painkillers and anti-inflammatories (NSAIDs) raise bleeding risk.
• Always inform the anticoagulant clinic and the doctor before any change; see atrial fibrillation and blood thinners: a family guide.

### Diabetes medicines (insulin, sulfonylureas, metformin and others)

• Herbs and foods that lower blood sugar: karela (bitter gourd) juice or tablets, fenugreek (methi) seeds, cinnamon, jamun, gymnema, neem, aloe vera juice, ginseng and psyllium. Combined with medicines, they can cause hypoglycaemia, particularly in older adults who eat irregularly; see low blood sugar in older adults: recognising and treating it.
• Ayurvedic and herbal "sugar" products sometimes contain hidden diabetes drugs or steroids.
• Metformin lowers vitamin B12 over time; see vitamin B12 in older vegetarians.
• Niacin (vitamin B3) in high doses can raise sugar.
• Monitor sugar and tell the doctor; see eating for diabetes after 60.

### Blood pressure and heart medicines

• Potassium supplements and salt substitutes with ACE inhibitors, angiotensin receptor blockers or potassium-sparing diuretics can cause dangerous high potassium.
• Liquorice (mulethi) products and some herbal tonics raise blood pressure and lower potassium, and interact with diuretics and digoxin.
• Grapefruit and some juices alter levels of certain calcium channel blockers and statins.
• Calcium supplements with thiazide diuretics can raise blood calcium; see calcium and vitamin D after 60: doses, food and sun.
• Digoxin: interacts with St John's wort, calcium and magnesium-containing antacids and high-fibre supplements.
• Red yeast rice contains a statin-like compound and should not be combined with statins.
• Stimulant herbs (ephedra, bitter orange, guarana) raise heart rate and blood pressure; avoid.
• Fish oil may lower blood pressure slightly.
• See eating for heart health after 60.

### Thyroid medicine (levothyroxine)

Calcium, iron, magnesium and antacids, soy products, high-fibre supplements and some multivitamins reduce absorption. Take levothyroxine on an empty stomach with water, and separate these by at least four hours, as the doctor advises. Biotin (in hair and nail supplements) can interfere with thyroid blood tests; tell the lab.

### Antibiotics, osteoporosis tablets and others

• Tetracyclines and quinolone antibiotics: bind to calcium, iron, magnesium, zinc and antacids; separate by several hours, as the pharmacist advises.
• Bisphosphonates (alendronate and others): must be taken with plain water on an empty stomach, with calcium and other supplements well apart.
• Iron interacts with levothyroxine, some antibiotics and calcium; see iron and anaemia in older adults.
• Antacids and acid reducers change absorption of several drugs and reduce B12 and magnesium; see acidity and reflux in older adults.

### Antidepressants, sedatives, epilepsy and Parkinson's medicines

St John's wort interacts with many antidepressants, anticonvulsants and warfarin; valerian, kava and ashwagandha may add to sedatives and raise fall risk (kava has been linked with liver injury); and iron or high-protein meals can reduce levodopa absorption, so ask about timing; see Parkinson's disease at home: a practical guide.

### Kidney disease

Many supplements are unsafe: potassium, magnesium, phosphate-containing products, vitamin A in excess, creatine, protein powders, certain herbs and Ayurvedic preparations with heavy metals or aristolochic acid; NSAIDs also harm. See eating with chronic kidney disease: a family guide and chronic kidney disease: a home care guide.

### Liver injury

Some herbal supplements (kava, concentrated green tea or turmeric extracts, comfrey and certain Ayurvedic and weight-loss products) have been linked with liver injury. Report yellow eyes, dark urine, pale stools, itching or severe tiredness at once.

### Cancer treatment and surgery

Antioxidants (high-dose vitamins C and E, beta-carotene) and many herbs may interfere with chemotherapy or radiotherapy, so ask the oncologist. Tell the surgeon and anaesthetist about all supplements; some (fish oil, vitamin E, ginkgo, garlic, ginger, turmeric, ginseng, St John's wort) are commonly paused before surgery, but only the surgical team can say which and for how long.

Foods and drinks that interact

• Grapefruit and pomelo: raise levels of some statins, calcium channel blockers, immunosuppressants and others.
• Leafy greens and vitamin K: with warfarin, as above.
• Tyramine-rich foods (aged cheese, fermented soy products, preserved meats) with older antidepressants (MAOIs).

Ayurvedic, herbal and traditional products

Ayurveda and traditional medicine are valued in many families, and some products have long histories of use, but they are not automatically safe with modern medicines or in older bodies.

• Tell the doctor and pharmacist about every product, including churna, bhasma, kadha, tablets, oils and tonics, and tell the Ayurvedic practitioner about all modern medicines, ideally letting them talk to each other.
• Beware of bhasma, rasa and metal-containing preparations, unless made and prescribed by a reputable practitioner with testing for heavy metals. Studies in India and abroad have found lead, mercury and arsenic in some products.
• Beware of products sold with claims of curing diabetes, blood pressure, kidney disease or arthritis, or of replacing medicines. Never stop prescribed medicines for them.
• Buy from licensed manufacturers, with batch numbers and AYUSH or FSSAI licences, and avoid unlabelled or imported products sold online; see spotting fake or poor-quality care products.

How to check safely: a step-by-step habit

1. Make a complete list of every medicine, supplement, herb, tonic, injection, eye drop, inhaler and cream, with the name, strength, dose, timing and reason. Include "natural" and over-the-counter products and those from other practitioners. Use the template in keeping a health record at home. 2. Bring all the actual bottles and strips (a "brown bag review") to a doctor or pharmacist at least once a year, and whenever something changes. 3. Ask before adding anything new, even vitamins: "Is this safe with my parent's medicines, kidneys and conditions?" 4. Ask the right questions: What is it for? Is it needed? What dose? How long? What could go wrong? Does it interact? Should it be taken apart from other medicines? 5. Check the label for ingredients, doses and warnings; see how to read a supplement label. 6. Use one pharmacy where possible, so that the pharmacist can see the whole picture. 7. Space doses properly, using a pill organiser and a written schedule; see pill organiser guide, setting up a weekly medicine box and giving medicines safely at home. 8. Start one thing at a time, so that effects and problems can be traced. 9. Watch for new symptoms after any change: rash, bruising, bleeding, black stools, dizziness, confusion, palpitations, nausea, jaundice, swelling, breathlessness, low sugar. 10. Review and trim supplements that are not clearly needed, with the doctor's agreement.

Red flags

Call 112 for chest pain, severe breathlessness, fainting, uncontrolled bleeding, black or bloody stools, vomiting blood, swelling of the face or throat, seizures, severe confusion or severe low sugar with drowsiness. Call the doctor the same day for new bruising, nosebleeds, dark urine, yellow skin, persistent vomiting or diarrhoea, rash or any suspected side effect.

When to ask a professional

Ask the pharmacist to review all medicines and supplements for interactions, and ask the doctor whether each is necessary. Ask the dietician about foods that interact. Ask an Ayurvedic or other practitioner to coordinate with the doctor. Seek urgent help for the red flags above.