Two running supplements have strong evidence behind them: caffeine and creatine. Caffeine helps on race day; creatine helps you recover across a training block. An IOC consensus statement puts both on its short list of supplements with good evidence. Magnesium and cordyceps are maybes, and greens powders are nutritional insurance rather than a performance aid.
Walk into any running shop and the wall of tubs makes a quiet promise: buy this, run faster. Most of it won’t. The supplement industry lives in the gap between what sounds plausible and what has been proven, and for runners that gap is enormous. Below is what each survivor can and can’t do, and the rules that matter more than any of the pills.
Does caffeine make you run faster?
Yes, caffeine is the most reliable legal performance aid in endurance sport. It blocks the adenosine receptors that tell your brain you’re tired. The ISSN position stand on caffeine finds aerobic endurance gets the most consistent benefit, at doses of 3–6 mg per kilogram of body weight. That is roughly 200–400 mg for a 65 kg runner. The catch is tolerance: habitual intake may blunt the response, which is why some runners cut back for a few days before a goal race. The most common timing is about 60 minutes before the start. And unlike everything else on this list, you almost certainly already own it.
Creatine spent decades typecast as a lifters’ supplement, and distance runners ignored it. That was a mistake. Creatine won’t move your steady marathon pace, but it helps with the work around it. It improves repeated hard efforts like surges and interval repeats, the effect the IOC consensus rates best supported. It may also speed recovery between hard sessions, with some evidence for less muscle damage and better glycogen restocking (ISSN position stand). The trade-off is weight: expect 1–2 kg of extra water in the muscle, which the IOC notes can work against you in endurance events. A daily 3–5 g fills your stores in about three to four weeks; a 5–7-day loading phase of about 20 g a day gets there faster. It’s not a race-day trick; it’s a training-block decision.
Does magnesium stop cramps?
Probably not: magnesium is where evidence and folklore part ways. It genuinely regulates muscle contraction, and there is some limited evidence it may help sleep, which is where most of your adaptation happens. What it probably won’t do is the thing it’s most often sold for. A Cochrane review of 11 trials found it unlikely to help the common, unexplained muscle cramps of older adults, and found no trials at all on exercise cramps. Treat it as a sleep-and-recovery aid, not cramp insurance — and check the form before you buy, because absorption varies wildly between them.
Cordyceps militaris, a medicinal mushroom, is the interesting outsider. Small studies point to improved oxygen use, higher VO₂max and longer time to exhaustion — exactly the levers endurance runners care about. The honest asterisk is large: most of that research is on recreationally active people in small samples, and whether it holds up in already-trained athletes is genuinely unknown. Promising, unproven, and — like creatine — it needs a few weeks in your system before you’d feel a thing.
Insurance, not performance
Greens powders — AG1 and its many imitators — have no direct evidence of making anyone faster, and anyone claiming otherwise is selling. What they can do is quietly fill micronutrient gaps during a heavy block, when appetite lags behind training load and the odd B vitamin, bit of zinc or dose of probiotics slips through the cracks. That’s a reasonable job for a supplement to do. Just price it as nutritional insurance, not a performance upgrade, and don’t expect the tub to show up in your splits.
The rules that matter more than the pills
None of this works in a vacuum, and a few principles decide whether any of it is worth doing at all:
- Fix deficiencies first. A supplement does the most when you were genuinely short of something. That’s an argument for a blood test, not a guess — especially for the classics runners run low on, like iron and vitamin D.
- Mind the tolerance. Caffeine rewards the occasional user and shrugs at the daily one. Cycle it down if race-day performance is the goal.
- Respect the timeline. Caffeine acts in an hour; creatine and cordyceps take weeks. Start the slow ones long before you need them.
- Buy tested, not just branded. Look for third-party certification — NSF, Informed Sport, Creapure — so you know what’s actually in the tub. For anyone who might be drug-tested, that isn’t optional.
The best supplement is the block of training you actually recovered from. Everything else is a rounding error.
Here’s the unglamorous truth the marketing buries: the thing that made you faster this season wasn’t in a tub. It was the ninety hard mornings, the long runs you didn’t skip, the sleep you finally took seriously. Capsules live at the margins; consistency is the whole story.