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Our approach
Elthio grades supplements from A to D based on
three factors: the bioavailability of the
supplement form, the presence of concerning
fillers or additives, and verification against
the NIH Dietary Supplement Label Database (DSLD).
Form quality assessments draw on published
absorption research, NIH ODS fact sheets, and
peer-reviewed literature. Final grades follow
consistent internal criteria and are never
influenced by commercial relationships with
supplement brands.
The A–D grade scale
A
Excellent
Highly bioavailable form with strong
absorption evidence. Clean label with no
concerning fillers. Consistent with NIH
registered products.
Examples: Magnesium Bisglycinate,
Methylcobalamin B12, Ubiquinol CoQ10,
Zinc Picolinate
B
Good
Good bioavailability with solid absorption
evidence. May contain minor fillers of low
concern, or a form that is good but not
optimal. Generally a sound choice.
Examples: Magnesium Citrate,
Cyanocobalamin B12, Zinc Gluconate,
Calcium Citrate
C
Average
Moderate bioavailability or a form with
mixed evidence. May contain fillers of
moderate concern. Functional but better
options usually exist.
Examples: Zinc Sulfate,
Calcium Carbonate (without acid),
some multivitamin blends
D
Poor
Low bioavailability form with weak
absorption evidence, or contains
high-concern fillers such as titanium
dioxide or artificial colors. A
significantly better alternative
usually exists at similar cost.
Examples: Magnesium Oxide,
supplements with titanium dioxide
or artificial colors
What determines the grade
Supplement form bioavailability
HIGH weight
Concerning fillers or additives
HIGH weight
NIH DSLD label verification
MEDIUM weight
Third-party testing certification
(if detectable)
BONUS
Filler concern levels
Not all fillers are equal. We flag fillers
based on published safety evidence:
High concern
Titanium dioxide, artificial colors
(Red 40, Blue 1, Yellow 5),
carrageenan, hydrogenated oils, BHT, BHA
Moderate concern
Magnesium stearate, silicon dioxide,
maltodextrin, carnauba wax
Low concern / acceptable
Cellulose, rice flour, hypromellose
(vegetable capsule), stearic acid
(plant-derived)
How we grade interaction evidence
For drug-supplement and supplement-supplement
interactions we apply an evidence strength
rating to every rule:
STRONG
Multiple RCTs or established
clinical guidance
e.g. Levothyroxine + Calcium (4-hour
separation), Warfarin + Vitamin K,
Iron absorption enhanced by vitamin C
MODERATE
Observational studies or pharmacological
reasoning with clinical support
e.g. Statins depleting CoQ10,
PPIs reducing magnesium absorption,
Metformin affecting B12 levels
LIMITED
Case reports, small studies, or
mechanistic reasoning only
e.g. Some herb-drug combinations,
timing based on absorption half-life
THEORETICAL
Based on mechanism of action only,
limited clinical confirmation
e.g. Theoretical nutrient competition
at transport level, extrapolation
from animal studies
Clinical review status
Interaction rules and severity ratings in
Elthio are compiled from public sources and
are pending review by a licensed
PharmD. Until that review is complete,
treat all interaction results as educational
starting points — not clinical decisions.
Always confirm with your pharmacist or
prescriber before changing medications or
supplements.
Our data sources
Drug-supplement interaction rules are
based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature including NIH ODS,
FDA drug labels, and peer-reviewed literature.
Supplement quality grades use NIH DSLD label
verification, NIH ODS fact sheets, and
peer-reviewed absorption research. We only
include interaction rules with identifiable
public sources:
NIH Office of Dietary Supplements
NIH DSLD — Dietary Supplement Label Database
FDA FAERS — Adverse Event Reporting System
NCCIH Herb-Drug Interactions
PubMed peer-reviewed literature
RxNorm drug database
What we don't do
- Accept payment from supplement brands
to influence grades
- Add interaction rules without identifiable
public sources
- Make medical claims or guarantee outcomes
- Use language that implies our tool replaces
a pharmacist or doctor
- Store or sell user data
Disagree with a result?
If a grade or interaction doesn't match guidance
from your pharmacist or doctor we want to know.
Your pharmacist's clinical judgment always takes
precedence over our tool.
Email us at
feedback@elthio.health
with the supplement name, the result you
received, and what your pharmacist said.
We review every report.
Review schedule
Full PharmD clinical review of interaction
rules is in progress. Until complete, rules
are refreshed against primary sources on a
rolling basis. Quality grading logic is
reviewed quarterly. This page was last
updated September 2026.
Elthio is an educational tool only —
not medical advice.
Always confirm supplement decisions with
your doctor or pharmacist.
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