Research on supplement and drug interactions — mechanisms, evidence, sources.
2026-07-18
Chronic alcohol use depletes magnesium through increased renal excretion and impaired intestinal absorption. Why supplementation is less effective while drinking continues, and how this connects to common symptoms.
Read →2026-07-18
Prednisone and other corticosteroids reduce the intestinal calcium absorption that vitamin D normally drives, while also increasing urinary calcium loss. What the NIH ODS documents about this interaction.
Read →2026-07-17
Calcium carbonate requires stomach acid to dissolve and absorb. PPIs suppress that acid, reducing calcium carbonate bioavailability. Calcium citrate does not depend on acid and absorbs better in low-acid conditions.
Read →2026-07-17
H2 receptor antagonists like famotidine reduce gastric acid, impairing the protein-unbinding step that releases dietary B12 for absorption. Less severe than PPIs, but relevant for people on chronic H2 blocker therapy.
Read →2026-07-17
Loop diuretics like furosemide cause substantial renal magnesium wasting by blocking the NKCC2 transporter. Thiazides have a similar but less severe effect. What the NIH ODS documents for people on chronic diuretic therapy.
Read →2026-07-16
Proton pump inhibitors, H2 blockers, calcium supplements, antacids, and certain antibiotics all reduce iron absorption through different mechanisms. Timing strategies that help, and why the interaction is often missed.
Read →2026-07-16
Vitamin D enhances calcium absorption through VDR-mediated intestinal transport — which is why they are commonly co-supplemented. But the combination carries a specific hypercalcemia risk with thiazide diuretics.
Read →2026-07-16
Long-term PPI use causes hypomagnesemia through a colonic transport mechanism that oral magnesium supplements cannot reliably fix. What the FDA safety communication documents and what it means for people on chronic PPI therapy.
Read →2026-07-15
In rheumatoid arthritis, folic acid co-prescription with methotrexate is standard of care that reduces toxicity. In cancer treatment, supplemental folate may reduce chemotherapy efficacy. The mechanism behind the difference.
Read →2026-07-15
High-dose calcium and iron compete for the DMT1 intestinal transporter. Taking them together at supplement doses reduces iron absorption by 30–60%. What the research shows and how to take both effectively.
Read →2026-07-15
Long-term proton pump inhibitor use impairs absorption of vitamin B12, iron, magnesium, and calcium through four distinct mechanisms. What the NIH ODS fact sheets document for each nutrient.
Read →2026-07-14
Proton pump inhibitors like omeprazole suppress the gastric acid needed to convert dietary iron to its absorbable form. Long-term PPI use is associated with iron deficiency in epidemiological studies.
Read →2026-07-14
Melatonin and alcohol both depress CNS activity — their sedative effects add. Alcohol also suppresses natural melatonin secretion, undermining the supplement's purpose even before the interaction risk.
Read →2026-07-14
Vitamin C enhances non-heme iron absorption by 2–4x through a well-understood chemical mechanism. When to take them together, who benefits most, and the one group that should be cautious.
Read →2026-07-14
Combining 5-HTP with SSRIs raises serotonin through two independent mechanisms simultaneously — increased production plus reduced clearance. What NCCIH documents and why the answer is not "yes."
Read →2026-07-13
Curcumin inhibits platelet aggregation through thromboxane B2 suppression — an effect INR testing does not capture. Combined with warfarin, the bleeding risk is broader than most people realize.
Read →2026-07-13
Ashwagandha raises T4 and T3 levels in human studies, creating a real interaction with levothyroxine. For people on thyroid medication, this additive effect can push hormone levels too high.
Read →2026-07-13
Both berberine and metformin activate AMPK to lower blood glucose, producing additive effects when combined. What this means for people managing type 2 diabetes with medication.
Read →2026-07-12
Magnesium is a cofactor in insulin receptor signaling. High-dose supplementation may modestly enhance insulin sensitivity and compound the glucose-lowering effect of sulfonylureas and insulin. What the evidence shows.
Read →2026-07-12
St. John's Wort induces CYP3A4, speeding up metabolism of contraceptive hormones and lowering their circulating levels. Case reports document breakthrough bleeding and unplanned pregnancies. What the evidence shows.
Read →2026-07-12
Rhodiola rosea has mild MAO-inhibiting properties and stimulant-like effects on dopamine and norepinephrine systems. Combined with prescription MAOIs or stimulants, these effects may be additive.
Read →2026-07-11
5-HTP directly increases serotonin production. Combined with SSRIs or MAOIs, it can produce serotonin syndrome — a serious and potentially dangerous reaction. What NCCIH documents and why this interaction is often missed.
Read →2026-07-11
Passionflower flavonoids modulate GABA-A receptors — the same system as benzodiazepines and z-drugs — producing additive sedation with CNS depressants including prescription sleep medications and alcohol.
Read →2026-07-11
Feverfew parthenolide inhibits platelet aggregation through collagen-induced activation and serotonin pathways, creating additive bleeding risk with warfarin, aspirin, and clopidogrel. What NCCIH documents.
Read →2026-07-11
Grape seed extract proanthocyanidins inhibit platelet aggregation via thromboxane A2 suppression and collagen-induced activation, creating additive bleeding risk with anticoagulants and antiplatelet drugs.
Read →2026-07-11
Silymarin inhibits CYP2C9 and CYP3A4, raising plasma concentrations of warfarin, cyclosporine, tacrolimus, and many other medications. Narrow-therapeutic-index drugs carry the most clinical concern.
Read →2026-07-10
Saw palmetto has been associated with antiplatelet activity, creating potential additive bleeding risk with warfarin, aspirin, and other anticoagulants. What NCCIH documents and what the evidence actually shows.
Read →2026-07-10
Glycyrrhizin inhibits 11-beta-HSD2, causing pseudo-hyperaldosteronism: sodium retention, potassium loss, and elevated blood pressure. This counteracts antihypertensives and worsens diuretic-related potassium depletion.
Read →2026-07-10
Green tea catechins chelate non-heme iron, reducing absorption. High-dose EGCG supplements also inhibit OATP drug transporters, with a documented 75% reduction in nadolol levels in one pharmacokinetic study.
Read →2026-07-10
Kava's kavalactones modulate GABA-A receptors — the same system as benzodiazepines — producing additive sedation. Separately, kava's documented hepatotoxicity risk compounds with acetaminophen, statins, and antifungals.
Read →2026-07-08
Black cohosh inhibits CYP2D6, the enzyme that converts tamoxifen to its active metabolite endoxifen. Reduced endoxifen may diminish tamoxifen efficacy. What NCCIH documents for breast cancer patients.
Read →2026-07-08
Echinacea stimulates NK cells, phagocytic activity, and cytokine production — effects that directly oppose immunosuppressants used after organ transplant or for autoimmune conditions. What NCCIH documents.
Read →2026-07-08
Valerenic acid modulates GABA-A receptors — the same system targeted by benzodiazepines and z-drugs. Combining valerian with CNS depressants produces additive sedation. What NCCIH documents.
Read →2026-07-07
Ashwagandha increases thyroid hormone levels and stimulates immune function — both create real interactions with levothyroxine and immunosuppressants like cyclosporine and tacrolimus. What NCCIH documents.
Read →2026-07-07
Curcumin inhibits platelet aggregation through thromboxane B2 suppression and inhibits CYP1A2 and CYP3A4, raising plasma levels of drugs like tacrolimus and cyclosporine. What NCCIH documents.
Read →2026-07-06
Berberine activates AMPK — similar to metformin — and inhibits CYP3A4, raising levels of drugs like cyclosporine. Both create real interactions with diabetes medications and CYP3A4-sensitive drugs.
Read →2026-07-06
Zinc chelates fluoroquinolone and tetracycline antibiotics in the GI tract, competes with iron at the DMT1 transporter, and at sustained high doses depletes copper via metallothionein induction. What the NIH ODS zinc fact sheet documents.
Read →2026-07-05
Statins inhibit the mevalonate pathway, which produces both cholesterol and CoQ10. Whether this depletion contributes to muscle symptoms is plausible but not conclusively proven. What NCCIH documents.
Read →2026-07-05
Metformin impairs B12 absorption through a calcium-dependent mechanism at the ileal membrane. Proton pump inhibitors reduce the gastric acid needed to release B12 from food. Who is most at risk.
Read →2026-07-04
Red yeast rice contains monacolin K — chemically identical to lovastatin. Combining it with a prescription statin is pharmacologically equivalent to taking two statins at once, substantially increasing the risk of muscle damage.
Read →2026-07-03
High-dose vitamin E supplements inhibit platelet aggregation and may potentiate warfarin. What the NIH ODS fact sheet documents and why dose matters more than most people realize.
Read →2026-07-03
Fluvoxamine inhibits CYP1A2, the enzyme that breaks down melatonin, raising melatonin blood levels roughly 17-fold. What this means for people on Luvox who take melatonin for sleep.
Read →2026-07-02
St. John's Wort reduces simvastatin and lovastatin levels via CYP3A4 induction. Red yeast rice contains monacolin K — pharmacologically identical to lovastatin — and should not be combined with prescription statins.
Read →2026-07-02
Ginkgo biloba contains ginkgolides that inhibit platelet activating factor, creating additive bleeding risk when combined with warfarin, aspirin, or clopidogrel. What NCCIH documents.
Read →2026-07-01
Garlic inhibits platelet aggregation and can induce CYP3A4, affecting warfarin, saquinavir, and other medications. What NCCIH and NIH ODS document.
Read →2026-07-01
Melatonin interacts with CNS depressants through additive sedation and with fluvoxamine through CYP1A2 inhibition — which can increase melatonin levels 17-fold. What the evidence shows.
Read →2026-07-01
ACE inhibitors, ARBs, and potassium-sparing diuretics all raise blood potassium. Adding a potassium supplement on top can push levels into a dangerous range. What the mechanisms are and who is at risk.
Read →2026-07-01
Calcium reduces the absorption of bisphosphonates, levothyroxine, fluoroquinolone and tetracycline antibiotics through chelation in the GI tract. What the evidence shows.
Read →2026-07-01
Vitamin D supplements interact with thiazide diuretics (hypercalcemia risk), corticosteroids, and anti-seizure medications. What the mechanisms are and why they matter.
Read →2026-06-30
Omega-3 fatty acids have antiplatelet effects that may interact with warfarin and other anticoagulants. The clinical evidence is mixed but the combination is worth understanding.
Read →2026-06-30
Magnesium supplements interact with antibiotics, bisphosphonates, and other medications through chelation in the GI tract — and some medications deplete magnesium over time. What the NIH ODS fact sheet documents.
Read →2026-06-30
Iron supplements can significantly reduce levothyroxine absorption through chelation in the GI tract. What the evidence shows and why it matters for thyroid patients.
Read →2026-06-30
St. John's Wort has one of the most extensive interaction profiles of any supplement. Three well-documented interactions — with warfarin, SSRIs, and oral contraceptives — and the mechanism behind each.
Read →