Supplement Evidence Library

Evidence library

Supplement Evidence Library

Independent, primary-source evidence on 37 of the most-searched supplement ingredients. For each one we cover the forms that matter, interactions and side effects, what the research actually supports, and a plain-language verdict — graded on the strength of the underlying studies, not on marketing claims.

Graded on independent evidence

Every ingredient we cover

37 deep-dive articles, each with a headline evidence grade. Open any card for forms, dosing, interactions, side effects, and the studies behind the verdict.

Moderate
Magnesium
Sleep, stress, blood pressure — which form matters.
 Contested
Omega-3
Heart, mood, inflammation — EPA/DHA dosing.
 Strong
Melatonin
Sleep onset, jet lag, dose-dependent effects.
 Moderate
Vitamin D
Deficiency, mood, immune — who actually needs it.
 High interaction risk
St John's Wort
Mild depression — with serious interaction risks.
 Moderate
CoQ10
Heart, energy, statin-related muscle pain.
 Moderate
L-Tyrosine
Stress resilience, focus under acute pressure.
 Moderate
L-Theanine
Calm focus, caffeine pairing, anxiety support.
 Moderate
Saffron
Mood, depression — what the 34-trial meta-analysis shows.
 Moderate
Garlic
Blood pressure — allicin, aged extract, real effect size.
 Moderate
NMN
NAD+ precursors, aging, energy — human evidence vs hype.
 Contested
Probiotics
Strain-specific benefits — which ones actually work.
 Weak-to-Moderate
Collagen
Skin, joints — hydrolyzed collagen and what trials show.
 Moderate
Berberine
Blood sugar, lipids — metabolic effects and dosing.
 Moderate
Ashwagandha
Stress, cortisol — KSM-66 and the evidence behind it.
 Strong
Creatine
Muscle, cognition — the most-studied supplement.
 Moderate
Stevia
Stevioside vs Reb A vs Reb M — which form actually works.
 Strong
Monk Fruit
Mogroside V grades, forms, and the thin human evidence.
 Contested
Aspartame
IARC 2B, NutriNet-Santé, JECFA ADI — what the evidence shows.
 Moderate-to-Contested
Sucralose
Gut microbiome shifts and glycemic effects in human RCTs.
 Weak-to-Moderate
Saccharin
The bladder-cancer scare that was rat-specific — resolved.
 Contested-to-Weak
Acesulfame-K
The unreplicated cancer cohort signal — what it means.
 Strong
Whey Protein
WPC vs WPI vs WPH vs native — MPS dose-response and the leucine trigger.
 Weak
Yeast Protein
Single-cell vegan protein — one manufacturer-funded RCT, weak evidence.
 Moderate-to-Strong
Plant Protein
Pea/soy/rice/hemp — parity with whey when dose and leucine are matched.
 Moderate
Tongkat Ali
Natural testosterone booster? What human trials actually show.
 Moderate
Psyllium Husk
Nature's Ozempic? LDL and glucose yes — weight loss, weak.
 Weak-to-Moderate
Bovine Colostrum
Liquid gold for immunity? Athlete URTI data, beauty claims thin.
 Weak
Glutathione
Skin brightening from within? Oral weak, IV unsafe.
 Moderate
Myo-Inositol
PCOS metabolic and ovulatory benefit — guideline-endorsed.
 Moderate
Nattokinase
Dissolves microclots? Modest BP effect, bleeding risk.
 Moderate
Astaxanthin
Internal sunscreen? Skin moisture yes, lipid claims weak.
 Weak
Lion's Mane
Brain fog cure? Small pilots, thin human data.
 Weak
Rhodiola
Adaptogen for burnout? Promising but methodologically weak.
 Weak
Shilajit
Mountain mineral pitch — weak data, heavy-metal safety caveat.
 Weak-to-Moderate
L-Glutamine
Leaky gut repair? One strong RCT in a narrow IBS subgroup; critical-illness harm signal.
 Moderate
Zinc-L-Carnosine
Gastric ulcer healing and H. pylori adjunct — Japan drug, US supplement.
Natural vs Organic
'Natural' has no legal definition; organic is certified — but neither is proven healthier.
Natural vs Chemicals
Why natural doesn't always mean safe, and chemical doesn't always mean dangerous.
 Moderate
Narcolepsy
Excessive daytime sleepiness & cataplexy — evidence-based treatments are prescription drugs; no supplement has adequate evidence.
 Strong
Chronic Rhinosinusitis
Saline irrigation is the strongest non-drug intervention; most supplements lack CRS evidence.
 Moderate-to-Strong
Rheumatoid Arthritis
DMARDs are standard of care; omega-3 fish oil is the best-supported supplement adjunct.
Evidence-grade legend

How we grade supplement evidence

Every ingredient carries one of four grades. The grade reflects the quality, consistency, and independence of the studies behind a claim — not how often the claim is repeated online.

Strong Strong

Multiple high-quality randomised trials or systematic reviews agree. Effect is consistent and clinically meaningful.

Moderate Moderate

Reasonable trial evidence, but with limits — smaller samples, mixed results, or benefits confined to specific groups.

Weak Weak

Early or low-quality evidence — a few small studies, observational data, or findings that have not been replicated.

Insufficient Insufficient

Not enough reliable human data to judge. Claims rest mainly on mechanism, animal studies, or expert opinion.

A separate flag

Some ingredients also carry a high interaction risk flag. This is independent of the evidence grade — a supplement can be well-studied yet still interact dangerously with common medicines, as with St John's Wort.

Consistent structure

What we cover in every ingredient article

The same six-part structure runs through all 37 deep dives, so you can compare ingredients like for like.

1
Forms & types
The specific forms that matter for absorption and effect — and the cheaper forms that often disappoint.
2
Interactions
Medicines, other supplements, and conditions that change how the ingredient behaves or raise its risk.
3
Side effects
What people actually report, how common it is, and the dose thresholds where problems tend to appear.
4
What works & what doesn't
The uses supported by solid evidence, separated clearly from the popular claims that don't hold up.
5
FAQ
Direct answers to the questions people ask most — dosing, timing, safety, and who should avoid it.
6
Citations
Every claim links to the original study, systematic review, or regulator — never to another blog.
Our methodology

We work from primary sources: peer-reviewed trials, systematic reviews, and regulator guidance. Evidence is weighted by quality and independence, and we trace the funding behind each study rather than relying on author self-disclosures alone. Where a claim rests on industry-funded or unreplicated work, we say so plainly.

Read how we research and grade evidence · See our full source list

Grades reflect the current body of evidence and are revised as new high-quality research is published.