What are your supplements doing to each other?
Free interaction checker. 110 documented interactions across 53 supplements and 20 prescription medication classes. No signup, no email.
Roughly half of the serious problems in this rule set involve a
prescription drug — so if you take one, add it below. That is where the checker earns its keep.
What do you take?
Any prescription medication?
Stackwise for iPhone
The app does this continuously — checks your whole stack, enforces the timing gaps, tracks what you actually take, and tells you which supplements measurably change how you sleep and recover.
Get the appEvery interaction in the set
One page each, with the mechanism and what to do about it.
Serious
- 5-HTP + L-Tryptophan — Double serotonin precursor load
- 5-HTP + St. John's Wort — Serotonin syndrome risk
- 5-HTP + SSRIs / SNRIs — Serotonin syndrome risk
- 5-HTP + MAOIs — Hypertensive and serotonergic crisis risk
- Berberine + Insulin or sulfonylureas — Hypoglycaemia risk
- Calcium + Thyroid hormone — Calcium blocks your thyroid medication
- Calcium + Tetracycline / quinolone antibiotics — Calcium inactivates the antibiotic
- EPA + Blood thinners (warfarin type) — Additive bleeding risk
- Ginkgo Biloba + Blood thinners (warfarin type) — Additive bleeding risk
- Iron + Thyroid hormone — Iron blocks your thyroid medication
- Iron + Tetracycline / quinolone antibiotics — Iron inactivates the antibiotic
- L-Tryptophan + SSRIs / SNRIs — Serotonin syndrome risk
- L-Tryptophan + MAOIs — Serotonergic crisis risk
- L-Tyrosine + MAOIs — Hypertensive crisis risk
- Magnesium + Tetracycline / quinolone antibiotics — Magnesium inactivates the antibiotic
- Potassium + ACE inhibitors / ARBs — Dangerous potassium build-up
- Potassium + Potassium-sparing diuretics — Dangerous potassium build-up
- SAM-e + SSRIs / SNRIs — Additive serotonergic effect
- St. John's Wort + Blood thinners (warfarin type) — St. John's Wort lowers warfarin levels
- St. John's Wort + SSRIs / SNRIs — Serotonin syndrome risk
- St. John's Wort + Hormonal contraception — Contraceptive failure risk
- St. John's Wort + Immunosuppressants — Transplant rejection risk
- St. John's Wort + Antiretrovirals — Loss of viral suppression
- St. John's Wort + Digoxin — Reduced digoxin levels
- St. John's Wort + Active chemotherapy — Reduced chemotherapy exposure
- Vitamin E + Blood thinners (warfarin type) — Additive bleeding risk
- Vitamin K + Blood thinners (warfarin type) — Vitamin K directly opposes warfarin
Worth knowing about
- 5-HTP + SAM-e — Additive serotonergic effect
- Alpha-Lipoic Acid + Insulin or sulfonylureas — Hypoglycaemia risk
- Ashwagandha + Thyroid hormone — Ashwagandha raises thyroid hormone
- Ashwagandha + Sedatives / sleep medication — Additive sedation
- Beet Root + Other blood pressure medication — Additive blood pressure drop
- Berberine + Alpha-Lipoic Acid — Additive blood sugar lowering
- Berberine + Metformin — Additive glucose lowering
- Berberine + Statins — Raised statin levels
- Bromelain + Blood thinners (warfarin type) — Additive bleeding risk
- Caffeine + Melatonin — Caffeine cancels your melatonin
- Caffeine + Lithium — Caffeine shifts lithium levels
- Calcium + Iron — Calcium blocks iron absorption
- Calcium + Digoxin — Arrhythmia risk
- Chondroitin + Blood thinners (warfarin type) — Additive bleeding risk
- Curcumin + Blood thinners (warfarin type) — Additive bleeding risk
- Curcumin + Active chemotherapy — Possible interference with treatment
- DHEA + DIM — Stacked hormone modulation
- EPA + Vitamin E — Additive bleeding risk
- EPA + Ginkgo Biloba — Additive bleeding risk
- EPA + Antiplatelets — Additive bleeding risk
- Fenugreek + Insulin or sulfonylureas — Hypoglycaemia risk
- Folate + Vitamin B12 — Folate can mask a B12 deficiency
- Garlic Extract + Blood thinners (warfarin type) — Additive bleeding risk
- Ginkgo Biloba + Antiplatelets — Additive bleeding risk
- Iodine + Thyroid hormone — Extra iodine destabilises thyroid dosing
- Iron + Acid reducers (PPIs) — PPIs reduce iron absorption
- L-Citrulline + Other blood pressure medication — Additive blood pressure drop
- Magnesium + Thyroid hormone — Magnesium reduces levothyroxine absorption
- Magnesium + Digoxin — Reduced digoxin absorption
- Melatonin + Sedatives / sleep medication — Additive sedation
- NAC + Active chemotherapy — Possible interference with treatment
- Niacin (B3) + Statins — Raised muscle injury risk
- Panax Ginseng + Blood thinners (warfarin type) — Ginseng can alter INR
- Panax Ginseng + MAOIs — Reported manic episodes
- Psyllium Husk + Iron — Fiber traps minerals
- Psyllium Husk + Thyroid hormone — Fiber reduces levothyroxine absorption
- St. John's Wort + SAM-e — Additive serotonergic effect
- St. John's Wort + Statins — Reduced statin effectiveness
- Valerian Root + Sedatives / sleep medication — Additive sedation
- Vitamin C + Active chemotherapy — Possible interference with treatment
- Vitamin E + Antiplatelets — Additive bleeding risk
- Zinc + Copper — Zinc depletes copper over time
- Zinc + Tetracycline / quinolone antibiotics — Zinc reduces antibiotic absorption
Minor
- Ashwagandha + Melatonin — Sedative stacking
- Berberine + Chromium — Additive blood sugar lowering
- Berberine + Fenugreek — Additive blood sugar lowering
- Caffeine + Rhodiola Rosea — Stimulant stacking
- Caffeine + L-Tyrosine — Stimulant stacking
- Calcium + Zinc — Calcium reduces zinc uptake
- Calcium + Magnesium — Large calcium doses crowd out magnesium
- Chromium + Insulin or sulfonylureas — Additive glucose lowering
- EPA + Garlic Extract — Additive bleeding risk
- EPA + Curcumin — Additive bleeding risk
- EPA + Resveratrol — Additive bleeding risk
- GABA + Valerian Root — Sedative stacking
- GABA + Sedatives / sleep medication — Additive sedation
- Ginkgo Biloba + Garlic Extract — Additive bleeding risk
- Iodine + Ashwagandha — Both push on the thyroid
- Iron + Zinc — Iron and zinc compete
- Magnesium + Zinc — High magnesium can reduce zinc uptake
- Manganese + Iron — Manganese and iron compete
- Melatonin + Valerian Root — Sedative stacking
- Potassium + Insulin or sulfonylureas — Potassium shifts with insulin
- Psyllium Husk + Zinc — Fiber traps minerals
- Psyllium Husk + Calcium — Fiber traps minerals
- Saw Palmetto + Antiplatelets — Possible additive bleeding risk
- Vitamin A + Vitamin D — Very high vitamin A can antagonise vitamin D
- Vitamin C + Vitamin B12 — High-dose vitamin C can degrade B12
Pairs that help each other
- Caffeine + L-Theanine — Theanine smooths caffeine
- Coenzyme Q10 + Statins — Statins deplete CoQ10
- Collagen Peptides + Vitamin C — Vitamin C is required for collagen synthesis
- Creatine + Beta-Alanine — Complementary performance mechanisms
- Curcumin + DHA — Complementary anti-inflammatory routes
- Iron + Vitamin C — Vitamin C multiplies iron absorption
- L-Citrulline + Beet Root — Two routes to the same nitric oxide bump
- Magnesium + Acid reducers (PPIs) — PPIs deplete magnesium
- Selenium + Iodine — Selenium protects the thyroid
- Vitamin B12 + Metformin — Metformin depletes B12
- Vitamin B12 + Acid reducers (PPIs) — PPIs reduce B12 absorption
- Vitamin D + Magnesium — Magnesium activates vitamin D
- Vitamin D + Vitamin K — K2 directs the calcium D absorbs
- Vitamin D + Calcium — Vitamin D unlocks calcium absorption
- Zinc + Copper — Keep the ratio right