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.

The protocols that actually matter (dose and timing)

Knowing a supplement "works" is only half the story. The proven ones only deliver if you take the right amount, and for some, at the right time. Here is what the strongest position stands and reviews actually recommend, so the few supplements worth your money earn their place.

Creatine. The fastest route to full muscle stores is a short "loading" phase of about 0.3 grams per kilogram of body weight per day (roughly 20 grams, split into four servings) for five to seven days, followed by 3 to 5 grams a day to maintain those stores. If you would rather skip loading, simply taking 3 to 5 grams a day reaches the same saturation point over three to four weeks, just more slowly Kreider 2017. Timing barely matters; consistency is what fills the tank, and a daily dose works whether you take it before or after training.

Caffeine. The performance "sweet spot" is 3 to 6 milligrams per kilogram of body weight, taken roughly 60 minutes before exercise. Pushing higher (around 9 mg/kg) does not add benefit and sharply raises the odds of jitters, racing heart, and stomach upset Guest 2021. For an 80 kg person that target is about 240 to 480 mg, which overlaps with everyday coffee intake, so there is rarely a reason to buy a dedicated pill.

Protein powder. The meta-analysis behind the "worth it" verdict found that protein supplementation boosts strength and muscle gains during resistance training, but the effect plateaus: beyond roughly 1.6 grams of total daily protein per kilogram of body weight, adding more did not produce further gains Morton 2018. Powder is a convenience, not a magic ingredient. If you already hit that target from food, a scoop adds nothing.

Vitamin D. This is the one where "more" can backfire, so the protocol is the opposite of a fixed dose: test first. Benefits cluster in people who are genuinely deficient, and a reasonable maintenance dose for most adults is in the 800 to 1,000 IU per day range, which is considered safe Rizzoli 2020. Mega-doses are not better, as the next section explains.

The omega-3 fine print: it is the dose, not the molecule

The cheat-sheet correctly files everyday fish-oil capsules under "weak evidence" for preventing heart attacks, and a large Cochrane review backs that up Abdelhamid 2020. But there is an important nuance worth understanding before you write off omega-3s entirely, because the picture changes dramatically with dose.

The American Heart Association's science advisory concluded that prescription-strength omega-3 fatty acids at 4 grams per day are an effective, safe option for lowering high triglycerides, a specific blood-fat problem, either alone or alongside other lipid-lowering drugs Skulas-Ray 2019. The key word is prescription. A typical over-the-counter fish-oil softgel contains only a few hundred milligrams of active EPA and DHA, so reaching a 4-gram therapeutic dose from a drugstore bottle could mean swallowing eight or more capsules a day. The advisory is explicit that these benefits come from concentrated, regulated formulations, not the standard supplements on the shelf Skulas-Ray 2019.

The takeaway is not "fish oil works after all." It is that a high, precisely-dosed, prescribed product for a diagnosed condition is a completely different thing from a bargain-bin capsule taken as general "heart insurance." If your triglycerides are high, that is a conversation to have with your doctor about a prescription, not a reason to double up on supermarket softgels. For everyone else, eating fish remains the better-supported strategy.

Who should be cautious (and when to ask a clinician)

"Natural" does not mean "harmless at any dose," and a few of the supplements on the cheat-sheet have real ceilings. The point here is not to scare anyone off, but to flag the situations where more is genuinely risky and where a quick word with a pharmacist or doctor is worth it.

Caffeine. A systematic review found that up to 400 mg a day is not linked to adverse effects in healthy adults, which is a useful ceiling to keep in mind once you add pre-workout, coffee, and energy drinks together Doepker 2018. The limit drops for some groups: pregnant women are generally advised to stay at or below 300 mg a day Doepker 2018. People with anxiety, heart-rhythm conditions, or who are pregnant should treat caffeine as something to discuss with their clinician rather than free.

Vitamin D. The tolerable upper intake level for adults is widely set at 4,000 IU per day, and even this is the subject of debate. In a three-year trial, hypercalcemia (dangerously high blood calcium) appeared in 0%, 3%, and 9% of participants taking 400, 4,000, and 10,000 IU per day respectively, and very high blood vitamin D levels were linked to faster bone loss, not stronger bones Rizzoli 2020. The lesson: the high-dose drops sold online are not a "the more the better" vitamin, and anyone considering doses above the upper limit should be doing so under medical supervision with blood monitoring.

Magnesium. The upper intake level for magnesium from supplements is 350 mg a day, set specifically because diarrhea is the first thing to go wrong past that point Costello 2023. In healthy people the kidneys clear any excess efficiently, so the worst case is usually loose stools Costello 2023. The important exception is anyone with reduced kidney function: because magnesium is cleared by the kidneys, impaired kidneys can let it build to genuinely dangerous levels, so people with kidney disease should not take magnesium supplements without a clinician's sign-off.

The quality problem nobody puts on the label

Even after you have picked a supplement with real evidence and a sensible dose, one question remains: is what is in the bottle actually what the label says? In the United States this is a bigger gap than most shoppers realise. Under the 1994 Dietary Supplement Health and Education Act, supplements are regulated more like food than like drugs, which means manufacturers do not have to prove safety or effectiveness to the FDA before selling a product; oversight is mostly after the fact Jagim 2023.

That gap shows up in testing. A 2023 review reported that, depending on the study, anywhere from 14% to 50% of analysed supplement samples tested positive for anabolic agents or other prohibited substances they were never meant to contain. One large analysis found a banned stimulant in over 28% of samples examined Jagim 2023. The risk is not evenly spread: pre-workout, "thermogenic" fat-burner, and muscle-building products are the most frequently adulterated categories Jagim 2023. That is the same fat-burner aisle the cheat-sheet already warned about, and the FDA has repeatedly issued public notifications about weight-loss capsules spiked with undisclosed prescription drugs.

The practical defence is third-party certification. The review recommends choosing products carrying an independent seal such as NSF Certified for Sport, Informed Sport, Informed Choice, or BSCG, which test for contaminants and confirm label accuracy Jagim 2023. One honest caveat: even a certified product reduces risk rather than eliminating it entirely, because no program can test for every possible contaminant Jagim 2023. Still, for the handful of supplements actually worth taking, paying a little more for a verified seal is the cheapest insurance on this whole page, especially if you are a competitive athlete subject to drug testing or simply do not want unlabeled drugs in your morning scoop.

Curious about a viral one? See whether chlorophyll water lives up to the hype.

References