Register · 17 entries · including 6 involving a medicine
Dietary supplement interactions
Some supplements interfere with each other; others make a medicine less effective or riskier. Each fact sheet gives a verdict, the level of evidence and what to do, with sources. To analyze your own supplement combination, use the checker.
Check my stackAll interaction entries
17 entries
| Combination | Verdict | What you need to know |
|---|---|---|
| St John's wort + Contraceptive pill Supplement + medicine | AvoidStrong evidence | St John's wort speeds up clearance of the pill's hormones: bleeding, possible ovulation. Read the fact sheet |
| St John's wort + Antidepressants Supplement + medicine | AvoidModerate evidence | Risk of serotonin syndrome: never combine without medical advice. Read the fact sheet |
| Caffeine + Melatonin Supplement + supplement | Take separatelyModerate evidence | Evening caffeine delays your body clock and shortens sleep: keep it to the morning. Read the fact sheet |
| Calcium + Iron Supplement + supplement | Take separatelyStrong evidence | At the same meal, calcium reduces iron absorption by 50–60%: take them separately if you are correcting a deficiency. Read the fact sheet |
| Coffee or tea + Iron Supplement + food | Take separatelyStrong evidence | Coffee and tea drunk with a meal greatly reduce iron absorption: wait at least one hour. Read the fact sheet |
| Levothyroxine + Calcium and iron Supplement + medicine | Take separatelyStrong evidence | Calcium and iron reduce levothyroxine absorption: leave at least 4 hours between doses. Read the fact sheet |
| Antibiotics + Calcium, magnesium, iron, zinc Supplement + medicine | Take separatelyStrong evidence | Tetracyclines and quinolones bind to minerals: the antibiotic may become ineffective. Read the fact sheet |
| Caffeine + Creatine Supplement + supplement | MonitorLimited evidence | Limited and conflicting evidence: no solid reason to take them separately. Read the fact sheet |
| Zinc + Copper Supplement + supplement | MonitorModerate evidence | High-dose zinc taken for months can cause copper deficiency. Read the fact sheet |
| Vitamin K + Vitamin K antagonist anticoagulants Supplement + medicine | MonitorModerate evidence | Vitamin K counteracts vitamin K antagonists: keep intake consistent and do not supplement without advice. Read the fact sheet |
| Omega-3 + Anticoagulants Supplement + medicine | MonitorModerate evidence | No increase in bleeding at usual doses; high-dose EPA slightly increases the risk. Read the fact sheet |
| Zinc + Iron Supplement + supplement | MonitorModerate evidence | At high doses on an empty stomach, iron reduces zinc absorption; with a meal, the effect disappears. Read the fact sheet |
| Magnesium + Melatonin Supplement + supplement | CompatibleLimited evidence | No known interaction, but the combination itself has not been studied much. Read the fact sheet |
| Magnesium + Zinc Supplement + supplement | CompatibleLimited evidence | Compatible at usual doses; very high-dose zinc interferes with magnesium. Read the fact sheet |
| Vitamin D + Calcium Supplement + supplement | CompatibleStrong evidence | A logical combination for bones, but with modest benefits and slightly more kidney stones. Read the fact sheet |
| Caffeine + L-theanine Supplement + supplement | Useful combinationModerate evidence | Studied combination: a little more precision and vigilance, modest effect. Read the fact sheet |
| Iron + Vitamin C Supplement + supplement | Useful combinationModerate evidence | Vitamin C increases iron absorption from a meal; its effect on stores is small. Read the fact sheet |
Other combinations flagged by the checker
These combinations do not have a fact sheet yet. Those without a source are based on a basic consistency rule, for example combining a stimulant with a sleep aid.
| Pair | Type | Reading | Sources |
|---|---|---|---|
| Glycine + Melatonin | Synergie | Melatonin + glycine: a sleep- and relaxation-focused profile. | Editorial rule, not source-backed |
| Ashwagandha + Rhodiola | Alerte | Ashwagandha + rhodiola: sometimes conflicting adaptogenic profiles. | Editorial rule, not source-backed |
| Ashwagandha + Caffeine | Alerte | Caffeine + ashwagandha may be inconsistent if you are looking for a stable effect. | Editorial rule, not source-backed |
| Caffeine + Rhodiola | Alerte | Caffeine + rhodiola can cause excessive stimulation in sensitive individuals. | Editorial rule, not source-backed |
| Alpha-GPC + Caffeine | Synergie | Alpha-GPC + caffeine: a possible focus combo, but keep it restrained. | Editorial rule, not source-backed |
| NAC + Zinc | Synergie | NAC + zinc: a neutral, fairly simple stack. | Editorial rule, not source-backed |
| Berberine + Caffeine | Alerte | Berberine + caffeine can be a little harsh on the digestive system. | Editorial rule, not source-backed |
Method
The checker does not give a score. It compares each pair in your selection with the table above, applies a few profile rules (several stimulants in the evening, too many calming products, more than 5 products), then displays a status and coverage: how many combinations in your stack our database was able to assess.
9 pairs out of 16 are based on cited studies. The others are editorial consistency rules, identified as such in the table.
- The four statuses
- Documented interaction
- Opposing rationale or redundancy
- Insufficient data
- No alerts within the scope covered
Limits
This table covers 19 common supplements. The entries also cover a few major interactions with medicines, but not all of them: they are no substitute for your pharmacist or doctor, who know your full treatment regimen.
For the highest-risk cases, also read our guide to dangerous interactions between popular supplements . If you are currently receiving treatment, discuss your stack with a healthcare professional before changing anything.
Frequently Asked Questions (FAQ)
How does the checker reach its verdict?
It does not assign a score. It displays one of four statuses (documented interaction, opposing mechanisms or redundancy, insufficient data, no alerts within the scope covered) and indicates how many combinations in your selection its database was able to assess. No alerts does not mean no risk: combinations not covered remain unknown.
Does an alert mean danger?
No. An alert flags opposing effects (stimulant versus sedative), redundancy or a documented reason for caution. It is something to watch for when simplifying your stack, not a diagnosis or a formal contraindication.
Which supplements interact with medicines?
The best-known examples are St John's wort, which makes the pill and many medicines less effective; calcium, iron and magnesium, which interfere with levothyroxine and certain antibiotics; and vitamin K, which counteracts VKA anticoagulants. Always tell your doctor or pharmacist about your supplements.
Why do some pairs not have a detailed fact sheet?
Because a fact sheet requires sufficient evidence: an understood mechanism and identifiable trials. Pairs without a fact sheet remain in the table with their indicative level, and the checker flags them in your analysis.