Supplement interaction checker
Select what you take and see what competes, what combines well, and what to separate.
Know what you're taking.
Manage your supplement stack, check interactions,
and track every dose.
Check your entire stack at once
Add everything you take. Every pair is checked automatically.
Get your timing right
Organised by absorption windows so nothing competes.
Daily check-in
Check off each dose. Build streaks. See what you took and when.
Scan a barcode
Point your camera at any bottle. Details fill in automatically.
Frequently asked questions
Where does the interaction data come from?
Every interaction is sourced from published, peer-reviewed research. Primary sources include the NIH Office of Dietary Supplements, PubMed-indexed clinical studies, and the USDA FoodData Central database. Each interaction entry links to at least one published citation.
Does 'no interactions found' mean the combination is safe?
No. It means we don't have published interaction data for that specific combination in our database. Absence of data is not evidence of safety. If you're unsure about any combination, consult a healthcare professional.
Can I check more than two supplements at once?
The web checker compares two supplements at a time. The OnDose app checks your entire stack at once and flags every interaction automatically, so you don't have to test each pair.
What do the severity levels mean?
Info (blue) means the supplements have a notable relationship worth knowing. Caution (amber) means they may compete for absorption and timing adjustments help. Warning (orange) flags a meaningful interaction worth discussing with a professional. Avoid (red) means published evidence suggests potential harm without medical supervision.
Is this medical advice?
No. This tool is for educational purposes only. It presents published research about supplement interactions but does not diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional before changing your supplement regimen.
Further reading
Zinc and iron: why timing matters
How these essential minerals compete for the same absorption pathway, and what to do about it.
Calcium and iron: the absorption problem
Why calcium can cut iron absorption by up to 50%, and the timing fix that solves it.
Magnesium and calcium: why order matters
Two essential minerals that compete for the same transporter. Which goes first?
Vitamin D and K2: do you need both?
D3 drives calcium absorption. K2 directs where it goes. The case for pairing them.
Supplements with food or on an empty stomach?
Fat-soluble vs water-soluble, and why the wrong timing wastes your money.
Morning vs evening: does timing matter?
Which supplements to take when, which ones don't care, and why.