The Cited Supplement Cheat-Sheet

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The supplement aisle is built to make everything look equally proven. It isn't. A handful of supplements have genuinely strong, repeatable evidence. Most of the popular ones have evidence that is thin, mixed, or paid for by the company selling the product. This cheat-sheet sorts the common ones into honest tiers, with a real citation behind each verdict. The point isn't to talk you into or out of anything — it's to let you spend your money where the science actually is.

How to read the tiers: Strong = multiple high-quality trials or a major position stand agree. Moderate = real signal, but smaller or mixed studies, or it only works in a specific situation. Limited = a little evidence, often weak, conflicting, or industry-funded. No good evidence = the marketing is doing the heavy lifting.

The cheat-sheet at a glance

The ones worth your money

Creatine — Strong

• The ISSN position stand calls creatine monohydrate "the most effective ergogenic nutritional supplement currently available" for increasing high-intensity exercise capacity and lean body mass during training. 1
• It's also one of the most-studied: the same review found no compelling evidence of harm from long-term use (up to 30 g/day for 5 years) in otherwise healthy people. 1
• Plain monohydrate is the proven (and cheapest) form. Fancier "advanced" forms charge more for no proven advantage.

Caffeine — Strong

• Caffeine "has consistently been shown to improve exercise performance when consumed in doses of 3–6 mg/kg body mass," with aerobic endurance showing the most consistent moderate-to-large benefit. 2
• More is not better — very high doses (around 9 mg/kg) add side-effects without adding benefit. 2

Whey / protein powder — Strong (but it's just protein)

• A meta-analysis of 49 studies found protein supplementation "significantly enhanced changes in muscle strength and size" during resistance training. 3
• The catch: the benefit came from hitting your total protein target, with little extra gain above roughly 1.6 g/kg/day. Powder is a convenience, not a special ingredient — real food protein does the same job. 3

The ones that depend — read the fine print

Vitamin D — Moderate, but only if you're deficient

• In people who already have adequate vitamin D, large trials of 2,000+ IU/day found no meaningful reduction in falls or fractures. 4
• The benefit shows up in people who are genuinely deficient or insufficient. So the honest move is to test, then treat — not to take it blindly. 4

Magnesium — Limited and situational

• Sleep: a 2025 randomized trial in poor sleepers found magnesium beat placebo on insomnia score, but the effect was small, with the biggest improvement in people whose dietary magnesium was already low. 5
• Leg cramps: a randomized JAMA Internal Medicine trial concluded "oral magnesium oxide was not superior to placebo" for older adults' nocturnal leg cramps — and credited much of the perceived benefit to a placebo effect. 6

The popular-but-weak ones (where marketing outruns evidence)

Omega-3 fish-oil pills — No good evidence for heart protection

• A Cochrane review of dozens of trials concluded that taking long-chain omega-3 supplements "does not benefit heart health or reduce our risk of stroke or death from any cause." 7
• That's about the pills. Eating oily fish as food is a different, more reasonable proposition. 7

BCAAs — Limited; usually redundant

• BCAAs alone can't fully switch on muscle building because they lack the other essential amino acids. A complete protein source (food or whey) provides "the full complement of indispensable amino acids," and the BCAA-only response is "less than" that. 8
• If you already eat enough protein, a separate BCAA tub is largely paying twice for less.

Collagen-for-everything — Limited, and the evidence is funding-dependent

• A 2025 meta-analysis of 23 trials in The American Journal of Medicine found the apparent skin benefits disappeared once industry-funded studies were removed: independently funded trials showed no effect on skin hydration, elasticity, or wrinkles. The authors concluded there is "currently no clinical evidence to support the use of collagen supplements to prevent or treat skin aging." 9
• This is the cleanest real-world example of "the studies that look best are the ones the seller paid for."

Fat-burners / thermogenics — No good evidence, real safety flags

• The FDA repeatedly finds weight-loss/fat-burner products spiked with hidden, undeclared drug ingredients — including, in one case, the active ingredient in a prescription drug that can dangerously lower blood pressure. 10
• Little proven benefit, meaningful risk: an easy skip.

"Detox," cleanses, and "greens" — No good evidence

• The NCCIH notes a review found "no compelling research to support the use of 'detox' diets for weight management or eliminating toxins from the body." 11
• Your liver and kidneys handle detoxification. A powder doesn't.

How to read a supplement claim (so you can do this yourself)

• "Clinically proven" ≠ proven. Ask: proven in how many people, for how long, versus a placebo? One tiny study isn't proof.
• Check who paid. If the flattering studies are funded by the maker — as with collagen — treat the result as a hypothesis, not a fact. 9
• Proxy outcome vs. real outcome. "Boosts a biomarker" or "activates a pathway" is not the same as "makes you healthier, stronger, or live longer."
• Look for the conditional. Several supplements only work in a subgroup (vitamin D if deficient, magnesium if intake is low). General claims hide that.
• Supplements are loosely regulated. In the U.S. a label can make claims without proving them first, and products are sometimes contaminated — so "it's on the shelf" guarantees nothing. 10
• Default to food and to the cheap, proven stuff. Creatine monohydrate and protein are inexpensive and well-evidenced; most premium "stacks" are not.

This cheat-sheet is general information, not medical advice. Supplements can interact with medications and conditions — check with your clinician before starting one, especially vitamin D dosing or anything during pregnancy.

References