What Supplements Interact with Medications?
Quick Answer
Many. Common dangerous interactions: St. John's Wort with antidepressants/birth control, fish oil with blood thinners, vitamin K with warfarin, calcium with thyroid meds, grapefruit with dozens of drugs. Always tell your doctor about supplements. If on any medication, check interactions before starting supplements.
Key Points
- St. John's Wort is the most dangerous supplement for interactions
- Vitamin K directly opposes warfarin
- Calcium blocks thyroid medication absorption
- Fish oil adds to blood thinner effects
- Always tell doctors about all supplements
Detailed Answer
Supplement-drug interactions are common and underappreciated. Here are the most important ones:
HIGH-RISK INTERACTIONS:
• St. John's Wort + SSRIs: Serotonin syndrome risk (potentially fatal) • St. John's Wort + Birth Control: Reduces effectiveness, unplanned pregnancy • St. John's Wort + Many drugs: Activates CYP450 enzymes, speeds drug metabolism
• Vitamin K + Warfarin: Vitamin K reverses warfarin. Eat consistent amounts, don't supplement.
• Grapefruit + Statins/Calcium blockers/etc: Inhibits CYP3A4, increases drug levels dangerously
MODERATE INTERACTIONS:
• Fish oil + Blood thinners: Additive anticoagulation, increased bleeding risk • Calcium + Thyroid meds (levothyroxine): Take 4+ hours apart, calcium blocks absorption • Iron + Many medications: Binds to drugs, reduces absorption of both • Magnesium + Antibiotics: Reduces fluoroquinolone absorption • Vitamin C + Aluminum antacids: Increases aluminum absorption (bad)
SPECIAL CASES:
• Melatonin + Immunosuppressants: May enhance immune function (opposite of drug goal) • CBD + CYP450 drugs: Affects metabolism of many medications • Ashwagandha + Thyroid meds: May enhance thyroid function, requires monitoring
Always disclose supplements to doctors and pharmacists. Use interaction checkers before new supplements.
Important Considerations
- NEVER start St. John's Wort if on any medication without pharmacist check
- Warfarin users must avoid vitamin K supplements
- Blood thinner users should discuss fish oil with doctor
Evidence Quality
Multiple high-quality studies support this
Key Sources:
- reviewSupplement-Drug Interactions: Clinical Review
- guidelineSt. John's Wort Drug Interactions Database
- reviewNatural Products and Drug Metabolism: CYP450 Review
Related Questions
Use drugs.com interaction checker, tell your pharmacist, or ask your doctor. Most pharmacies have databases that check supplements too. Don't guess.
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About this information: Our recommendations draw from peer-reviewed clinical trials, systematic reviews, and the same medical databases your doctor uses. These statements have not been evaluated by the FDA. Supplements are not intended to diagnose, treat, cure, or prevent any disease.
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