A supplement store carries thousands of products, but fewer than a dozen have a consistently confirmed effect. Here are five that hold up under meta-analysis: exact doses, how long each takes to work, and a list of what you can safely cross off your shopping list.
The supplement industry is built so that a product's marketing budget has almost nothing to do with the strength of evidence behind it. Before you pay, ask three questions.
Is there a body of evidence, or a single study? One trial on twelve college students is a hypothesis, not a fact. Cochrane and the scientific panels at EFSA evaluate the full body of research, and that is the level worth relying on.
Who was studied? Effects found in a cell culture or in rodents routinely fail to reproduce in humans. "Boosts metabolism in vitro" is not a promise of weight loss.
How large is the effect? A 0.4% gain in endurance can be statistically significant and completely invisible to a recreational athlete. Everything below has an effect you can feel in the gym or see in your training log.
💡 The priority rule: supplements account for 2–5% of your results. Calorie balance, daily protein, training consistency, and sleep account for the other 95%. Buying a tub before those four are in place is like adding a spoiler to a car with no engine.
The most studied sports supplement in history — hundreds of controlled trials over more than thirty years. Creatine increases the phosphocreatine stored in muscle, the fuel for short, powerful efforts. That lets you get one or two extra reps at your working weight, and from there the accumulated training volume does the rest.
With daily intake alongside resistance training, lean mass gains over 4–12 weeks run roughly 0.9–1.8 kg above control groups, and strength gains come in at 5–15%. The effect reproduces in men and women, in young and older adults; in older adults creatine is additionally being studied as a countermeasure to sarcopenia.
The working protocol is 3–5 g of monohydrate daily, at any time of day, including rest days. Full muscle saturation takes 3–4 weeks. The accelerated option is a loading phase of 20 g per day (four 5 g doses) for 5–7 days, then a 3–5 g maintenance dose. The only gain here is speed: after a month both approaches land in the same place, and loading more often causes stomach discomfort.
You cannot get this much from food. Per USDA data, beef and salmon contain roughly 4–5 g of creatine per kilogram of raw product, so matching a supplement dose would mean eating a kilogram of meat every day.
In healthy people, long-term intake at doses up to 5 g per day has not shown any decline in kidney function. The confusion comes from lab work: creatine predictably raises blood creatinine — the marker used to assess the kidneys — without damaging the organ itself. That is why you should tell your doctor you take creatine before bloodwork. With existing kidney disease, use the supplement only under medical supervision.
The most predictable ergogenic aid there is. Caffeine blocks adenosine receptors and lowers your perceived effort: the same workload feels easier, so you finish the set or hold the pace. Endurance gains in studies run around 2–4%, strength gains 2–7%. For a marathon runner, 2–4% is several minutes off the finish time.
3–6 mg per kilogram of body weight, 45–60 minutes before training. For a 70 kg person that is 210–420 mg. EFSA considers single doses up to 200 mg and up to 400 mg per day safe for healthy adults, so the top of the athletic range is territory for experienced users, not a starting point. Begin at 3 mg/kg.
| Source | Serving | Caffeine |
|---|---|---|
| Espresso | 30 ml | ~63 mg |
| Drip coffee | 240 ml | ~95 mg |
| Instant coffee | 240 ml | ~62 mg |
| Black tea | 240 ml | ~47 mg |
| Green tea | 240 ml | ~28 mg |
| Energy drink | 250 ml | ~80 mg |
| Caffeine tablet | 1 tablet | 100–200 mg |
⚠ Caffeine's half-life is 5–6 hours, and longer in some people. In controlled research, a 400 mg dose taken six hours before bed cut total sleep time by about an hour — and participants did not notice the impairment. An evening workout with a pre-workout is a direct route to sleep loss that erases everything the supplement gave you.
Protein powder is not an anabolic or a "chemical" — it is dried milk protein. It works not on its own but as a tool for hitting your daily target. A meta-analysis of 49 studies published in the British Journal of Sports Medicine found that muscle gains from increasing protein plateau at around 1.6 g per kilogram of body weight per day. If you already hit that with food, a tub adds nothing.
The value of powder is convenience and leucine: about 30 g of whey isolate delivers ~25 g of protein and 2.6–2.8 g of leucine, and roughly 2.5 g of leucine per meal is considered the threshold for triggering muscle protein synthesis.
| Source | Serving | Protein | Leucine | Cost per serving |
|---|---|---|---|---|
| Whey isolate | 30 g | 25 g | ~2.7 g | $1.00–1.40 |
| Chicken breast | 120 g | 27 g | ~2.2 g | $0.60–0.85 |
| Cottage cheese, 5% | 150 g | 25 g | ~2.4 g | $0.55–0.80 |
| Eggs | 4 large | 25 g | ~2.1 g | $0.70–1.00 |
| Cooked lentils | 350 g | 31 g | ~2.2 g | $0.45–0.65 |
The table leads to a conclusion sellers dislike: ordinary food is cheaper and does the same job. Powder earns its place where food physically will not fit — a packed schedule, travel, or a high daily target paired with a small appetite.
The only supplement on this list that does not work for everyone — only for people who start out deficient. In someone with a normal 25(OH)D level, extra capsules improve neither strength nor endurance. In someone deficient, they improve both, noticeably.
NIH defines deficiency as a 25(OH)D level below 30 nmol/L, insufficiency as 30–50 nmol/L, and sufficiency as 50 nmol/L and above. The recommended daily allowance is 600 IU (15 mcg) for ages 1–70 and 800 IU (20 mcg) after 70. The tolerable upper limit for adults is 4,000 IU per day.
Above the 50th parallel, skin synthesis of vitamin D essentially shuts down from October through March — the angle of sunlight is simply too low. That covers much of northern Europe, Canada, and the northern United States. The sensible sequence: test 25(OH)D, set a dose with your doctor if you are deficient, and retest after 8–12 weeks.
⚠ Vitamin D is fat-soluble and accumulates in the body. Taking "10,000 IU just in case" without testing is not prevention — it is a hypercalcemia risk. Doses above 4,000 IU per day belong under medical supervision with regular bloodwork.
The least famous item on the list, with a genuinely solid evidence base. Beta-alanine raises muscle carnosine, and carnosine buffers acidity — the burn you feel on the last few reps. Pooled data show an average performance gain of about 2.8% in efforts lasting from 30 seconds to 10 minutes.
The key caveat is that the window is narrow. Beta-alanine is useless for a one-rep max, where acidity never builds up, and equally useless past the 25-minute mark. Its zone is intervals, rowing, 100–400 m swimming, CrossFit, and high-rep sets.
The dose is 3.2–6.4 g per day, split into 0.8–1.6 g portions. Carnosine saturation takes 4–10 weeks, so a single dose "before training" accomplishes nothing — even though that is exactly how it is usually packed into pre-workout blends. Single doses above 800 mg typically cause paresthesia, a tingling in the face and hands; the sensation is harmless, passes in 30–60 minutes, and splitting the dose solves it.
| Supplement | Daily dose | When to take | Effect appears in | What it does |
|---|---|---|---|---|
| Creatine monohydrate | 3–5 g | Any time, daily | 3–4 weeks | Strength, lean mass |
| Caffeine | 3–6 mg/kg | 45–60 min pre-workout | Immediately | Endurance, focus |
| Whey protein | Whatever the gap requires | Any time | Works via total protein | Hitting 1.6 g/kg |
| Vitamin D | 600–800 IU (test first) | With a fat-containing meal | 8–12 weeks | Only if deficient |
| Beta-alanine | 3.2–6.4 g, split | Daily, any time | 4–10 weeks | Efforts of 30 sec – 10 min |
| Supplement | The claim | What the research shows |
|---|---|---|
| BCAAs | Muscle growth, anti-catabolism | No added benefit when total protein is adequate: three amino acids are not enough, synthesis requires the full set of essentials |
| Glutamine | Recovery, immunity | No confirmed effect in healthy people eating a normal diet |
| Tribulus | Raises testosterone | Controlled trials show no increase in testosterone in healthy men |
| L-carnitine | Fat burning | At supplement doses it does not increase fat oxidation on a normal diet |
| Garcinia cambogia | Weight loss | Difference from placebo stays within about 1 kg — clinically meaningless |
| ZMA | Testosterone, sleep quality | Works only where zinc or magnesium is genuinely deficient |
A word on the most durable myth of all — "fat burners." Thermogenic blends do raise energy expenditure slightly, but the magnitude is on the order of 50–100 kcal per day. That is less than one banana, and it disappears entirely inside the margin of error of estimating what you ate. Exactly one ingredient in them works, and that is caffeine, which costs twenty times less on its own.
💡 Buying order on a limited budget: creatine first — it is the cheapest thing that works and delivers the largest effect. Then caffeine, ideally from coffee. Protein powder only if you cannot close your protein target with food. Vitamin D strictly on the basis of a blood test. Beta-alanine last, and only if your sport falls inside its window.
In most countries supplements are regulated as food, not medicine: the manufacturer is not required to prove efficacy before going to market. Independent testing regularly finds labels that do not match contents — from "amino spiking" that inflates protein on paper to undeclared stimulants and prohormones. For an athlete subject to drug testing, that is a risk of a ban for something they never knowingly took.
💡 A practical filter: look for third-party certification on the package (Informed Sport, NSF Certified for Sport) and a short ingredient list. Creatine monohydrate should contain creatine monohydrate — "transport matrices" and "buffered forms" cost more and do not outperform plain monohydrate in head-to-head studies.
And the main point: none of these five supplements compensates for chronic sleep loss, a protein shortfall, or a training plan that never progresses. They amplify what already exists — they create nothing from scratch.
The 1.6 g/kg target stays abstract until you see a real day in numbers. Photograph your plate — the bot calculates calories and macros, shows how much protein you are missing, and suggests what will close the gap.
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