Marathon training is simple on paper: run more, recover well, repeat. In real life, work stress, sore legs, bad sleep, and missed meals add friction. That’s where supplements can help, but only if you use them for a clear job: fill a gap, support hard sessions, or fix a problem you can’t solve with food alone.
This article breaks down supplements for athletes preparing for marathons in plain terms. You’ll learn what’s worth considering, what to skip, how to time it, and how to avoid the common mistakes that waste money or upset your stomach on race day.
Start here before you buy anything
Supplements can’t replace training, sleep, and enough calories. If you’re under-fueled, no pill fixes that. Before you add anything, run through these basics:
- Can you finish most runs without bonking, dizzy spells, or intense cravings later?
- Do you sleep 7-9 hours most nights?
- Do you eat carbs at most meals and protein a few times a day?
- Do you have regular blood work if you’ve had low iron, heavy fatigue, or frequent illness?
If those are shaky, start there. Then use supplements to tighten the bolts.
The big rocks for marathon training
Carbs during long runs and races (this is your top “supplement”)
If you take only one thing from this page, take this: carbs during long runs matter more than any capsule. Call it nutrition, call it supplementation, call it fuel. It’s the same job.
Most runners do well aiming for 30-60 grams of carbs per hour on long runs, then pushing toward 60-90 grams per hour for longer efforts if their gut can handle it. You don’t guess this on race week. You practice it.
- Options: gels, chews, drink mix, or real food that’s low fiber and easy to chew
- Pair carbs with water and sodium so it absorbs well
- Train your gut by using the same plan weekly
For practical pacing and fueling math, use a calorie and carb planning tool like the marathon pace calculator to map effort and time, then match your fuel plan to the hours you’ll be out there.
Electrolytes, with sodium as the main one
Sweat rate and sweat sodium vary a lot. That’s why some runners finish long runs with salt crust on their shirt and others don’t. Sodium helps you hold onto the fluid you drink and can reduce the risk of cramps tied to low sodium intake, especially in hot conditions.
A simple approach:
- For long runs, try 300-600 mg sodium per hour and adjust from there
- If it’s hot, humid, or you sweat heavy, you may need more
- Avoid chugging plain water for hours with no sodium
Want a more exact starting point? The Gatorade Sports Science Institute sweat rate worksheet gives a straightforward way to estimate your fluid loss and tighten your plan.
Protein and creatine for durability (yes, even for runners)
Marathon training breaks tissue down. You rebuild it with food, especially protein. Many runners under-eat protein because they focus on carbs (which you still need). A helpful target for endurance training often lands around 1.2-1.7 g/kg/day depending on your training load and goals. If you struggle to hit that with meals, protein powder is a cheap, low-friction fix.
Creatine helps with high-intensity work and strength training. That matters for marathoners who lift, run hills, or do intervals. It won’t turn you into a sprinter, but it may support better training quality. Some runners notice a small weight bump from water stored in muscle. That can be fine, but if it messes with how you feel, skip it.
- Protein powder: 20-40 g after training or to top up daily intake
- Creatine monohydrate: 3-5 g per day, any time, take it consistently
For a science-based overview of creatine safety and use, see the International Society of Sports Nutrition position stand on creatine.
Performance supplements with decent evidence
Caffeine for pacing, focus, and perceived effort
Caffeine can make marathon pace feel more manageable, which is a big deal late in the race. It can also sharpen focus when you’re tired. But it’s easy to mess up if you don’t test it. Too much can spike your heart rate, wreck your gut, or push you to go out too fast.
Common dosing sits around 1-3 mg/kg, taken 30-60 minutes before hard sessions or race start. Some runners prefer smaller “top-ups” later (like a caffeinated gel around mile 14-18). Practice this in training.
- Test your dose on a long run first
- Avoid trying a new caffeine product on race day
- If caffeine hurts your stomach, try lower dose or different form (gum, gel, coffee)
For safety basics and how caffeine affects the body, the Mayo Clinic’s caffeine overview is a solid reference.
Beetroot juice (dietary nitrates) for some runners
Beetroot juice can improve blood flow and exercise efficiency in some athletes, especially at moderate to hard effort. Results vary. Some runners feel a real boost, others feel nothing, and a few get stomach issues.
How to test it:
- Try 2-3 hours before a tempo run or long-run marathon-pace segment
- Use a product that lists nitrate content if possible
- Don’t pair it with antibacterial mouthwash right before dosing, since mouth bacteria help convert nitrates
Sodium bicarbonate (high risk, sometimes useful)
Sodium bicarbonate can help with short, hard efforts by buffering acid. For marathoners, it’s mostly relevant if you do intense intervals and want an edge in those sessions. The downside: gut distress is common. If you’re prone to stomach trouble, this is not your friend.
If you’re curious, test it far from key workouts, and never on race day as a first try.
Health and recovery supplements that can matter
Iron (only when you need it)
Low iron can crush endurance. It can also look like “just tired from training,” which is why it gets missed. Runners, especially menstruating athletes, vegetarians, and those with a history of low ferritin, should take iron seriously.
But don’t self-prescribe high-dose iron. Too much causes side effects and can be harmful. Get labs and follow your clinician’s plan.
For a clear medical overview, the NIH Office of Dietary Supplements iron fact sheet covers dosing, interactions, and warning signs.
Vitamin D (common gap, simple fix)
Many people come up low on vitamin D, especially in winter or if they get little sun. Low vitamin D can affect bone health, immune function, and muscle performance. If you train through winter or live far from the equator, ask for a blood test. If you supplement, take it with a meal that has fat.
Omega-3s (helpful for some, not magic)
Omega-3s may support heart health and help manage inflammation. They won’t erase soreness, but they can support general health when your training load climbs. If you already eat fatty fish a few times a week, you may not need a pill.
Magnesium (only if you’re low or your diet is thin)
Magnesium gets marketed as a cramp cure. The evidence there is mixed. Still, magnesium matters for nerve and muscle function, and many diets run low. If you want to try it, start with food first (nuts, beans, greens, whole grains). If you supplement, choose a form that’s gentler on your stomach and don’t mega-dose. Too much can cause diarrhea fast.
Collagen or gelatin with vitamin C for tendon support
If you deal with nagging tendon issues (Achilles, patellar tendon, plantar fascia), collagen or gelatin might help when paired with loading work. The idea is simple: give your body the building blocks, then do the rehab that tells your tendon to use them.
A common protocol runners use:
- 10-15 g collagen peptides or gelatin
- Take it 30-60 minutes before strength or rehab work
- Add vitamin C (or have it with a vitamin C rich food)
This won’t replace smart training, but it can support it.
Supplements marathoners often buy that don’t help much
BCAAs (usually redundant)
If you eat enough protein, you already get BCAAs. Save your money for quality carbs and sodium during long runs.
“Test boosters,” fat burners, and mystery blends
These products often hide behind “proprietary blends” and hype. They can also carry a higher risk of contamination. If you race under rules, that risk matters.
Megadose antioxidants (high-dose C and E)
Antioxidants from food are great. Very high-dose supplements may blunt some training adaptations in some cases. You don’t need to fear a normal multivitamin, but think twice before taking huge doses to “speed recovery.”
Timing and dosage that fit real training weeks
Most supplement plans fail because runners treat them like a one-time fix. Build a routine that matches your training week.
Daily basics (if they fit your needs)
- Protein powder: use as needed to hit your daily protein
- Creatine: 3-5 g daily if you lift and tolerate it well
- Vitamin D: only if labs or lifestyle suggest a gap
- Iron: only with confirmed low status and a plan
Workout-specific (practice in training)
- Long runs: carbs + sodium + fluids, same products you’ll race with
- Key sessions: caffeine if you tolerate it and it supports the goal
- Optional trial: beetroot juice before some tempo sessions
Race-week rules that prevent chaos
- Don’t introduce new supplements
- Don’t “load” random products out of fear
- Stick to the foods and fuels your gut already knows
Safety, quality, and label traps
Supplements aren’t regulated like drugs. Labels can lie, and contamination happens. If you compete in tested events or you just want lower risk, choose products that use third-party testing.
Look for seals like NSF Certified for Sport or Informed Sport on the label. And read the ingredient list. If it has 40 ingredients and you can’t name half, skip it.
Watch for common interactions
- Iron can interact with calcium and some medications and can cause constipation
- Caffeine plus pre-workout blends can push your dose too high
- Magnesium can interfere with some meds and can cause diarrhea at high doses
If you take prescription meds or you’re pregnant, check with a clinician or sports dietitian before adding anything.
Putting it together with a simple marathon supplement plan
If you want a clean plan that covers most runners, start here and adjust based on your sweat rate, gut, and training.
Tier 1: high payoff, low drama
- Carbs during long runs (build toward your race target)
- Sodium and fluids matched to your sweat
- Protein intake that fits your training load
Tier 2: useful when targeted
- Caffeine for key workouts and race day (tested first)
- Creatine if you lift and want better strength and repeat efforts
- Vitamin D or iron based on labs and risk factors
Tier 3: experiment only if you like testing
- Beetroot juice for some runners
- Collagen or gelatin for tendon-prone athletes
- Sodium bicarbonate only if your gut tolerates it and you have a clear use case
Where to start this week
Pick one training run in the next 7 days and treat it like a fueling practice run. Plan your carbs per hour, your sodium per hour, and how much you’ll drink. Then write down what happened: energy, stomach, pace drift, bathroom stops, and how you felt the next day.
After two to three weeks, you’ll have real data, not guesses. That’s when supplements for athletes preparing for marathons start to make sense: they become tools you use on purpose, not habits you copy from someone else.
If you want extra help building a plan that fits your body and your race, consider working with a sports dietitian. The Academy of Nutrition and Dietetics directory can help you find a credentialed pro who understands endurance training.