Caffeine for Ultras: How Much, When, and When to Stop

For caffeine in an ultramarathon, most runners do well on about 3 to 5 mg per kg of body weight across the whole race, taken in small doses of 1 to 2 mg per kg rather than one large hit, and saved for the night section or the low point rather than spent at the start. Stop about six hours before you plan to sleep, because caffeine taken that late still cut sleep in a controlled study.

That may be less than you’d guess. The research on caffeine is strong for races up to a few hours and thin for races that last a day, so most of what follows is about applying good short-race evidence sensibly to a long one.

How much caffeine actually helps?

Between 3 and 6 mg per kg of body weight is the range with consistent evidence, and benefits may start as low as 2 mg per kg. The International Society of Sports Nutrition’s position stand puts aerobic endurance at the top of the list for consistent gains, and notes that very high doses around 9 mg per kg bring more side effects without adding benefit (Guest et al., 2021). The IOC’s supplement consensus lists caffeine as one of only a handful of supplements with good evidence behind it (Maughan et al., 2018).

In numbers, for a 65 kg runner:

For safety context, the European Food Safety Authority judged that single doses up to 200 mg, and habitual intake up to 400 mg a day, raise no safety concerns for healthy adults (EFSA, 2015). An ultra can tempt you well past that by stacking coffee at the start, caffeinated gels and cola at the checkpoints. Count all three.

Does it still work in a race that lasts all day?

Probably, but nobody has proven it in an actual ultramarathon. Almost all caffeine trials last under three hours. The closest long test is a 100 km laboratory cycling time trial, where 6 mg per kg before the start plus small top-ups every 15 minutes made no difference to finishing time or to power in the hard efforts (Hunter et al., 2002). Eight cyclists in a lab isn’t a 100 km trail race, but it’s a useful brake on the idea that more caffeine for longer equals more speed.

Where caffeine does earn its place in ultras is the night. The ISSN position stand concludes caffeine reliably helps attention and vigilance, and may help both thinking and physical performance under sleep deprivation in some people (Guest et al., 2021). Near the equator, night falls at about the same time all year, somewhere between about 7.10 and 7.30 pm in the Klang Valley and earlier in Sabah. A 100 km that starts at dawn puts most runners on a dark, rooty trail for six to ten hours, when foot placement and decisions matter more than raw speed.

When should you take it?

Later than most people think. Caffeine is usually taken about 60 minutes before exercise in studies, but it doesn’t have to be front-loaded. In an Australian Institute of Sport study, cyclists rode two hours steady and then a time trial. Caffeine at 6 mg per kg improved the time trial whether it was taken an hour before the start or spread through the ride. Switching from sports drink to cola for the final 40 minutes of steady riding and the time trial worked just as well, on only about 1.5 mg per kg of caffeine (Cox et al., 2002).

That’s the most useful finding for ultra runners: a small dose late can do the job. So a sensible pattern is:

• Morning start: your normal coffee with breakfast, nothing extra.
• First half: little or no extra caffeine. Use caffeine-free gels.
• From dusk or the first real low point: 1 to 2 mg per kg every two to three hours, from cola, a caffeinated gel or a small coffee at a checkpoint.
• Last third: one more top-up if you need to stay sharp on technical ground.

The total for that pattern often lands around 3 to 5 mg per kg across the whole race, spread over many hours rather than taken at once.

When should you stop?

About six hours before you want to sleep. In a controlled trial, 400 mg of caffeine taken six hours before bedtime still cut total sleep by more than an hour compared with placebo (Drake et al., 2013). That matters more than people expect after an ultra, because recovery starts with the first night’s sleep and the drive home.

Work backwards from your likely finish. If you expect to cross the line at 4 am and want to sleep by 6 am, your last meaningful caffeine was around midnight. If you’ll be driving back from Kuala Kubu Bharu or up the Karak Highway after the race, think about that drive too: being too wired to sleep and then too tired to drive is a bad combination. Sleep first, drive later.

Will caffeine dehydrate you in the heat?

Not at the doses that help. In a three-day study of 50 habitual coffee drinkers, four cups of coffee a day carrying 4 mg per kg of caffeine produced the same hydration markers as the same volume of water (Killer et al., 2014). The ISSN position stand also supports caffeine at 3 to 6 mg per kg for endurance exercise in the heat (Guest et al., 2021).

So a kopi at a midnight checkpoint counts towards your fluid, not against it. The bigger hydration risk in a long Malaysian race is usually drinking too much, which we cover in Dehydration vs Hyponatremia in Ultras.

Do you need to cut caffeine before race day?

You don’t have to. In a study of 40 trained cyclists, heavy daily caffeine users improved their time trial just as much from a 6 mg per kg dose as light users did (Gonçalves et al., 2017). Withdrawal headaches in race week are a bigger risk than reduced sensitivity. Keep your normal morning coffee and don’t experiment.

What goes wrong?

The usual problems are a jittery stomach, a racing heart and a crash a few hours later. Caffeine responses vary widely between people, partly for genetic reasons, and anxiety and poor sleep after caffeine are both more common in some runners than others (Guest et al., 2021). A gut that is already struggling in the heat at 2 am doesn’t need a double espresso.

Three practical rules handle most of it:

Count every source. Write down the caffeine in each gel, cola and coffee you plan to use. Labels vary a lot, and some gels have none.

Rehearse it. Try your night-time caffeine plan on a long run that goes into the evening, ideally on a hot afternoon. If cola at hour five gives you a stitch, find out on a Sunday at Bukit Kiara, not on race night.

Keep the carbohydrate going. Caffeine doesn’t replace fuel. Cola works in studies partly because it also carries sugar. Keep to your carbohydrate plan from How Many Carbs Per Hour Do You Need for Running?, and see when to take your gels if you’re swapping some for caffeinated ones.

A sample plan for a 100 km that starts at dawn

Take a 65 kg runner aiming for 20 hours, starting at 6 am. Normal coffee at 4.30 am. No extra caffeine until about 6.30 pm, as the light goes. Then roughly 100 mg at 7 pm (a caffeinated gel or small coffee), 100 mg at 10 pm and 65 mg around 1 am from cola. That’s about 265 mg across the race, roughly 4 mg per kg, never more than about 1.5 mg per kg at once. Finish around 2 am, last caffeine five hours earlier, a little short of the six-hour mark, so expect a slow first hour of sleep.

Your numbers will differ. Plug your own body weight in, then put the plan into our race fueling calculator alongside carbohydrate, fluid and sodium so you can see the whole race on one page. For everything else that changes between 50 km and 100 km, read our ultra marathon nutrition guide.

References

1. Guest NS, VanDusseldorp TA, Nelson MT, et al. (2021). International Society of Sports Nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 18(1), 1. doi:10.1186/s12970-020-00383-4
2. Maughan RJ, Burke LM, Dvorak J, et al. (2018). IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine, 52(7), 439-455. doi:10.1136/bjsports-2018-099027
3. EFSA Panel on Dietetic Products, Nutrition and Allergies (2015). Scientific opinion on the safety of caffeine. EFSA Journal, 13(5), 4102. doi:10.2903/j.efsa.2015.4102
4. Hunter AM, St Clair Gibson A, Collins M, Lambert M, Noakes TD (2002). Caffeine ingestion does not alter performance during a 100-km cycling time-trial performance. International Journal of Sport Nutrition and Exercise Metabolism, 12(4), 438-452. doi:10.1123/ijsnem.12.4.438
5. Cox GR, Desbrow B, Montgomery PG, et al. (2002). Effect of different protocols of caffeine intake on metabolism and endurance performance. Journal of Applied Physiology, 93(3), 990-999. doi:10.1152/japplphysiol.00249.2002
6. Drake C, Roehrs T, Shambroom J, Roth T (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 9(11), 1195-1200. doi:10.5664/jcsm.3170
7. Killer SC, Blannin AK, Jeukendrup AE (2014). No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One, 9(1), e84154. doi:10.1371/journal.pone.0084154
8. Gonçalves LS, Painelli VS, Yamaguchi G, et al. (2017). Dispelling the myth that habitual caffeine consumption influences the performance response to acute caffeine supplementation. Journal of Applied Physiology, 123(1), 213-220. doi:10.1152/japplphysiol.00260.2017

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