What the research says, what it doesn't, and when to take each one.

Most supplements marketed to runners are noise. But there are a handful with enough evidence to justify a place in your routine — not as replacements for training, sleep, or food, but as genuine marginal gains once everything else is dialled in.

Brand I use: Thorne Creatine Monohydrate

Creatine is one of the most studied supplements in sports science. It saturates your muscles' phosphocreatine stores, allowing faster ATP regeneration during high-intensity efforts.

The direct effect on steady-state marathon pace is negligible. Where creatine earns its place for runners is recovery and race-day surges. Research on runners completing a 30 km time trial found that creatine supplementation significantly reduced inflammation and muscle damage markers. When co-ingested with carbohydrates, it enhances glycogen resynthesis between sessions. And it improves your capacity for pace changes and finishing kicks — the moments that often define a race.

The trade-off is a modest increase in body mass (1–2 kg from water retention). Whether the recovery benefits outweigh the extra weight depends on where you are in your training cycle.

How to take it: 5 g/day, every day, no loading or cycling needed. Takes about four weeks to fully saturate. Time of day doesn't matter.

Other brands worth considering: Momentous Creatine (Creapure, NSF Certified for Sport), Myprotein Creapure, Naked Creatine (Creapure), Klean Athlete Creatine (NSF Certified), Optimum Nutrition Micronised Creatine. The key is creatine monohydrate with third-party testing. Look for the Creapure logo or NSF/Informed Sport certification.

Brand I use: Puresport Cordyceps

Cordyceps militaris is a fungus with a growing body of research around improved oxygen utilisation at the cellular level.

The most cited study showed that after three weeks at 4 g/day, recreationally active subjects had a significant improvement in VO2max (+4.8 ml/kg/min) and time to exhaustion (+70 seconds) versus placebo. One week showed a trend but no significant VO2max change, suggesting the effects accumulate.

The honest caveat: most studies used recreationally active subjects, not trained endurance athletes. Sample sizes are small. A 2026 narrative review in Nutrients concluded that results are promising but not yet definitive. I treat cordyceps as "probably helps, definitely doesn't hurt" — not a replacement for intervals, but if it edges VO2max even modestly over an 18-week block, that's worth something.

How to take it: 1–3 g/day, consistently, for at least three weeks before expecting any effect. I take it with breakfast.

Other brands worth considering: Real Mushrooms Cordyceps (extract from fruiting body, not mycelium), Host Defense Cordyceps (Paul Stamets' brand, mycelium-based), Four Sigmatic Cordyceps Elixir, Nootrum Cordyceps. The distinction that matters: look for cordyceps militaris (cultivated, better studied) over sinensis, and fruiting body extract over mycelium-on-grain, which dilutes potency.

Brand I use: Puresport Magnesium

Magnesium is involved in over 300 enzymatic reactions including muscle contraction, ATP activation, and nerve signalling. Roughly half of adults in Western countries don't meet the recommended intake, and runners lose additional magnesium through sweat.

For runners, it works on three fronts. Muscle recovery: it regulates the balance between contraction (calcium) and relaxation (magnesium), reducing soreness and tightness. Sleep quality: magnesium glycinate interacts with GABA receptors, improving sleep onset and depth — which for runners in peak training weeks is arguably its biggest value. And electrolyte balance: when magnesium is low, your hydration strategies become less effective regardless of how many sodium tabs you take.

The cramp evidence is actually weaker than most people assume. A Cochrane review found magnesium wasn't consistently better than placebo for nocturnal cramps in the general population. But the picture improves in active populations with confirmed low intake, which describes most distance runners during high-volume blocks.

How to take it: 200–350 mg of elemental magnesium before bed. Glycinate for sleep and recovery, citrate for general use. Avoid oxide (poor absorption). Start at 150–200 mg and adjust upward.

Other brands worth considering: Doctor's Best High Absorption Magnesium (glycinate/lysinate chelate), Natural Vitality Calm (citrate powder, good for mixing into water), NOW Foods Magnesium Glycinate, Solgar Magnesium Citrate. If you prefer topical, BetterYou Magnesium Spray is widely available in Europe. Form matters more than brand here: glycinate for sleep, citrate for general use, malate for energy and recovery.

Brand I use: Whatever is nearest. Coffee, tablets, or caffeinated gels on race day.

Caffeine is the most well-established legal ergogenic aid in endurance sport. It blocks adenosine receptors, reducing perceived effort and delaying fatigue. The effect is typically 2–4% in time trial performance — for a 3:00 marathon, that's roughly 4–7 minutes.

The catch is tolerance. Four espressos a day will blunt the acute race-day boost. Some runners taper caffeine the week before a goal race to resensitise. I've done this for my last two marathons and found the effect noticeable, though the withdrawal headaches are unpleasant.

How to take it: 3–6 mg/kg body weight, 30–60 minutes before your effort. For a 75 kg runner, that's 225–450 mg. I take 200 mg with breakfast on race morning and another 100 mg via caffeinated gel around 30 km. Save strategic dosing for races and key workouts.

Other options: For race day gels (only if you tested during your workouts), Maurten Caffeinated Gel 100 (100 mg caffeine), SiS GO + Caffeine Gel (75 mg), and Precision Fuel & Hydration PF 30 Caffeine Gel (100 mg) are all widely used. For tablets, Myprotein Caffeine Pro (200 mg) and Pro Plus (50 mg per tablet, easy to dose precisely) are cheap and effective. Plain coffee works fine for training. The delivery method matters less than the dose and timing.

Brand: AG1 (formerly Athletic Greens)

AG1 is a different category from the four above. It's not targeting a single mechanism. It's a greens powder combining 75+ vitamins, minerals, probiotics, adaptogens, and plant extracts into one daily scoop. Think of it as nutritional insurance rather than a performance supplement.

Why it's here: There is no published research linking greens powders directly to improved running performance. That needs to be said upfront. What AG1 does is close micronutrient gaps, which for runners juggling high training loads, work, and family is where it earns its place. It covers B vitamins, zinc, folate, vitamin C, vitamin E, and probiotics for gut health in a single serving. It's NSF Certified for Sport and has four clinical trials showing it supports nutrient status and digestion.

The honest case for AG1 is practical, not pharmacological. During a marathon block, when you're running 80+ km a week and your appetite swings between ravenous and non-existent, micronutrient intake becomes inconsistent. AG1 won't make you faster. But it can keep your immune system intact and your gut functioning when training stress is at its highest. That matters more than most runners acknowledge.

The honest case against it is price. At roughly €2.50–3.50 per serving on subscription, it's significantly more expensive than buying a basic multivitamin and a separate probiotic. And because AG1 uses proprietary blends, you can't verify the dose of every individual ingredient. It also lacks meaningful amounts of vitamin D, iron, and calcium, so it doesn't replace everything.

How to take it: One scoop in 250–350 ml of cold water, first thing in the morning on an empty stomach for best absorption. Daily consistency matters more than any single serving.

Other brands worth considering: Supergreen Tonik (fully transparent label, no proprietary blends), Huel Daily Greens (cheaper, available in Europe), Athletic Nutrition Greens (budget option). If you'd rather skip greens powders entirely, a quality multivitamin (Thorne Multi-Vitamin Elite is a good option for athletes) plus a standalone probiotic achieves a similar outcome at lower cost.

Creatine

Cordyceps

Magnesium

Caffeine