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💊 Evidence-Based
🌿 African Herbals & Foods Included
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Drug Interaction Checker
Search any drug, herbal remedy, or food — including Nigerian traditional medicines like zobo, bitter kola, agbo, and black seed — and see every interaction instantly.
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Understanding Drug Interactions
A drug interaction occurs when a medicine, food, drink, or supplement changes the way another medicine works in the body — either making it stronger, weaker, or causing unexpected side effects. Drug interactions are responsible for an estimated 3-5% of hospital admissions worldwide, yet the vast majority are entirely preventable with proper awareness.
The risk increases with polypharmacy — taking five or more medicines simultaneously — which is common in patients managing hypertension, diabetes, and heart disease concurrently. The more medicines you take, the more important it becomes to check every new prescription and even over-the-counter purchase.
The Three Types of Drug Interactions
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Pharmacokinetic
One drug changes how the body absorbs, distributes, metabolises, or excretes another. The most common example involves liver enzymes (CYP450) — one drug can speed up or slow down the breakdown of another, raising or lowering its blood level.
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Pharmacodynamic
Two drugs have additive or opposing effects at the same target. For example, two medicines that both lower blood pressure taken together can cause a dangerous drop. Or two sedating drugs taken together can cause respiratory depression.
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Chemical / Physical
Drugs bind to each other in the gut and become inactive before being absorbed. Calcium in dairy products binding to antibiotics like ciprofloxacin and doxycycline is a classic example — separating them by 2 hours prevents the interaction.
🌿 Herbal Medicines and Supplements
Herbal remedies and dietary supplements are widely used worldwide — yet patients rarely disclose this to their doctor or pharmacist. This creates hidden drug interactions invisible to the prescriber. Well-documented examples include St. John's Wort reducing the effectiveness of antidepressants and contraceptives, ginkgo biloba increasing bleeding risk with anticoagulants, and high-dose garlic supplements affecting warfarin.
Our database includes interactions with herbal and traditional preparations from multiple traditions — including West African medicinal plants and foods — making it one of the most comprehensive checkers for patients using traditional alongside conventional medicine.
Always tell your pharmacist or doctor about every herbal remedy, supplement, and traditional medicine you take. There is no such thing as a completely harmless supplement when combined with prescription medicines — the interactions are real and some are serious.
The Most Clinically Important Drug Interactions
These are the interactions responsible for the greatest proportion of preventable drug-related hospital admissions worldwide:
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Warfarin + NSAIDs (Ibuprofen, Naproxen, Diclofenac)
One of the most common causes of serious drug-related bleeding worldwide. NSAIDs are widely available over the counter — patients on warfarin must use paracetamol (acetaminophen) instead and always check with a pharmacist before buying any painkiller.
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Opioids + Benzodiazepines
The FDA has issued a black box warning for this combination, which accounts for the majority of opioid-related overdose deaths. Both depress breathing through different mechanisms, and their combined effect is synergistic — far more dangerous than either alone.
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SSRIs + Tramadol
Combining antidepressants (SSRIs like sertraline, fluoxetine) with tramadol causes serotonin syndrome — a potentially fatal reaction causing agitation, high fever, muscle rigidity, and seizures. This is the most commonly missed dangerous interaction in general practice globally.
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MAOIs + Serotonergic Drugs
MAO inhibitors combined with SSRIs, SNRIs, TCAs, or triptans cause severe and potentially fatal serotonin syndrome. A mandatory 14-day washout period is required between stopping an MAOI and starting any serotonergic drug.
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Nitrates + PDE5 Inhibitors (Sildenafil, Tadalafil)
GTN (nitroglycerin) spray or tablets combined with erectile dysfunction medicines causes catastrophic blood pressure collapse. Men with heart disease who use GTN for chest pain must never take sildenafil, tadalafil, or vardenafil. This combination has caused deaths.
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Rifampicin + Many Drugs
Rifampicin (rifampin) is the most potent liver enzyme inducer in clinical use. It dramatically reduces the blood levels of hormonal contraceptives, antiretrovirals, warfarin, antifungals, and many other drugs. Anyone starting TB treatment needs a full medication review.
🍊 Food and Drink Interactions
Some of the most important drug interactions involve everyday foods and drinks — not just other medicines:
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Grapefruit Juice
Grapefruit permanently inhibits intestinal CYP3A4 enzymes for up to 72 hours. This can raise blood levels of simvastatin up to 16-fold, and significantly affects many other drugs including some calcium channel blockers, immunosuppressants, and certain antiretrovirals.
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Vitamin K Foods (Leafy Greens)
Spinach, kale, broccoli, and other leafy greens are rich in vitamin K, which directly opposes warfarin. Patients on warfarin do not need to avoid these foods — but must keep their intake consistent week to week. Sudden large changes destabilise INR control.
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Dairy Products
Calcium in milk, yoghurt, and cheese chelates (binds) certain antibiotics — particularly ciprofloxacin, doxycycline, and tetracyclines — in the gut, reducing antibiotic absorption by 40-90%. Separate these antibiotics from dairy by at least 2 hours.
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Alcohol
Alcohol interacts with almost every CNS-active drug — sedatives, opioids, antidepressants, antihistamines, and antiepileptics all become significantly more dangerous. Metronidazole (Flagyl) combined with any alcohol causes a severe disulfiram-like reaction. Metformin combined with heavy drinking increases lactic acidosis risk.
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Coffee and Caffeine
Coffee reduces levothyroxine (thyroid hormone) absorption by up to 40% when taken simultaneously — take thyroid tablets 30-60 minutes before morning coffee. Ciprofloxacin also significantly raises caffeine levels by inhibiting the liver enzyme that breaks caffeine down.
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Food Timing with Medicines
Some drugs must be taken with food (artemether-lumefantrine for malaria, rilpivirine for HIV, metformin for diabetes tolerance), others on an empty stomach (bisphosphonates like alendronate, levothyroxine). Taking medicines at the wrong time relative to food significantly affects how well they work.
Understanding Severity Ratings
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Contraindicated — These medicines must never be taken together. The risk of serious harm or death is too high to justify this combination under any circumstances. Examples: nitrates + sildenafil, MAOIs + SSRIs, warfarin + miconazole oral gel.
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Major — A serious interaction that may require changing one of your medicines or close monitoring. Tell your doctor or pharmacist as soon as possible. Examples: warfarin + fluconazole, digoxin + amiodarone, lithium + ibuprofen.
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Moderate — A significant interaction. Your doctor or pharmacist should be aware and may adjust your dose or recommend additional monitoring. Examples: omeprazole + clopidogrel, aspirin + ibuprofen, metformin + trimethoprim.
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Minor — A mild interaction. Usually manageable without changing treatment, but worth being aware of. Examples: azithromycin + warfarin, cetirizine + alcohol, calcium + iron (reduced absorption if taken simultaneously).
Not finding an interaction does not guarantee safety — our database covers 3,000 clinically validated pairs but no database covers every possible combination. Always confirm with a pharmacist or physician before starting, stopping, or changing any medication.
Who Should Check for Drug Interactions?
Drug interaction checking is important for everyone who takes medicines — but certain groups face higher risk and should check every new prescription:
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Older Adults
Age-related changes in liver and kidney function alter how drugs are processed. Polypharmacy is common. Drug interactions are more likely and more severe.
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People on 4+ Medicines
Taking five or more medicines (polypharmacy) dramatically increases the probability of at least one significant interaction being present.
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Anticoagulant Users
Warfarin, rivaroxaban, apixaban, and similar blood thinners interact with hundreds of drugs. Any new medicine needs checking first.
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Antidepressant Users
SSRIs and SNRIs interact with many pain medicines, migraine treatments, and other antidepressants through serotonin mechanisms.
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Supplement Users
St. John's Wort, ginkgo, garlic, omega-3, glucosamine, and many other supplements have documented drug interactions that patients rarely mention to prescribers.
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New Prescriptions
Every time a new medicine is added to an existing regimen, checking for interactions with current medicines is essential — including OTC drugs and supplements.
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Not Sure? Ask a Pharmacist
Our licensed pharmacists can review your full medication list — including prescription drugs, supplements, and herbal remedies — and advise on interactions, timing, and safe alternatives.