How much caffeine is allowed during an ultramarathon?

November 21, 2025 •

2 min read

According to the International Society of Sports Nutrition, consuming 3–6 mg of caffeine per kilogram of body weight can improve endurance performance by 2–4%. For ultramarathoners, understanding how much caffeine is allowed during an ultramarathon is critical for managing fatigue and improving focus in the later stages of a race.

Quick Summary

Optimal caffeine intake for ultramarathons involves strategic, lower doses, especially late in the race, based on distance and personal tolerance to enhance performance and alertness.

Key Points

Dosage Moderation: For ultramarathons, focus on lower, sustained doses (e.g., 50 mg/hr) rather than large, infrequent amounts to prevent adverse side effects.
Strategic Timing: Time your caffeine intake for the latter stages of the race or during nighttime hours when fatigue is most acute, reserving it for when you need it most.
Practice in Training: Always test your caffeine strategy, including product type, dose, and timing, during long training runs to assess your individual tolerance.
Know Your Sensitivity: Individual response to caffeine varies significantly due to genetics and habitual use, so find a dose that benefits you without causing jitters or GI issues.
Avoid Overconsumption: Excessive caffeine intake can impair performance through increased anxiety, gastrointestinal distress, and sleep disruption.
Timing is Key: Since caffeine can take up to an hour to peak, consume it 45-60 minutes before you need the maximum effect.

The Role of Caffeine in Ultrarunning Performance

Caffeine is a central nervous system stimulant that can benefit endurance athletes by blocking adenosine receptors, reducing the perception of effort and pain. This effect helps manage the mental and physical fatigue common in ultramarathons and can increase alertness and concentration during long events. While it was once thought to primarily aid fat oxidation, this is now considered a minor factor.

General Dosing Recommendations

For ultramarathons, lower, consistent doses are generally recommended over large amounts to sustain effectiveness and minimize side effects. A typical effective dose for many ultramarathoners is around 50 mg per hour. The International Society of Sports Nutrition suggests 3–6 mg/kg of body weight for shorter endurance events, but for ultras, a 'drip feed' approach is often better.

Strategic Timing by Race Length

Timing caffeine intake is crucial and should depend on race length and personal energy levels.

For races under 6 hours: Consider taking caffeine (around 50 mg/hr via gels or chews) in the second or third hour.
For 50K or 50-Mile races: Use caffeinated products in the latter half for a boost. A steady 50 mg/hr is often effective.
For 100-Mile or longer races: Delay caffeine use until significant fatigue or sleepiness occurs, frequently during night sections. Doses might increase to 100 mg/hr for a few hours at night but should stop before sunrise for better post-race sleep.

Risks and Side Effects of Overconsumption

Too much caffeine can negatively impact performance. Side effects include gastrointestinal distress, anxiety, increased heart rate, and sleep disruption.

Comparing Common Caffeine Sources

Understanding the caffeine content of products and practicing with them during training is vital.


Product Category	Example Product	Typical Caffeine Content	Considerations
Energy Gels	Gu Roctane Coffee	~70 mg	Convenient, provides carbohydrates simultaneously.
	Clif Shot Double Espresso	~100 mg	Higher concentration, may require less frequent intake.
	Huma Chia Energy Gel Plus	~25 mg	Lower dose, good for sensitive individuals or frequent intake.
Drinks	Tailwind Endurance Fuel	35 mg per 100 calories	Easy to consume, but dosage can be less precise with sips.
	Cola (12 oz)	~34-54 mg	Can cause GI distress due to carbonation and acidity.
Capsules/Tablets	50 mg Tablet	50 mg	Precise dosing, no calories, but easy to overconsume.
Natural	Drip Coffee (7 oz)	~115-175 mg	High and variable dose, best used pre-race if a regular consumer.

The Importance of Training and Individual Sensitivity

Individual responses to caffeine vary based on genetics and usage habits. Testing your caffeine strategy in training is essential to find the right dose, timing, and product that works for you without adverse effects.

Conclusion: A Strategic and Safe Approach

Determining how much caffeine is allowed during an ultramarathon requires considering individual needs, race length, and tolerance. While caffeine is not banned by WADA, a moderate, strategic approach is key for performance and safety. By testing your strategy, understanding risks, and using sensible dosing, caffeine can be a valuable tool in completing an ultramarathon strongly. For more details on caffeine research, refer to the Journal of the International Society of Sports Nutrition.

Frequently Asked Questions

No, caffeine was removed from the World Anti-Doping Agency (WADA) banned substances list in 2004, and there are no restrictions on its use in ultramarathons.

For most ultramarathon distances, a conservative dose of about 50 mg per hour is generally well-tolerated. Some strategies for longer races suggest up to 100 mg/hr during specific periods of fatigue.

For races over six hours, it's best to wait until the second half or when mental fatigue becomes noticeable. For overnight races, reserve caffeine until after midnight or when feeling sleepy.

Yes, even regular caffeine users can benefit. The effects on alertness and reduced perceived effort still apply, though the boost might feel less pronounced. There is no strong evidence that abstaining pre-race significantly increases the benefit.

Overconsumption can lead to anxiety, jitters, gastrointestinal issues, increased heart rate, and interrupted sleep, which can all negatively impact your race.

Caffeine pills offer precise dosing but lack carbohydrates. Caffeinated gels provide both fuel and caffeine simultaneously. The best option depends on your overall fueling strategy and personal preference, which should be tested in training.

No, research indicates that the diuretic effect of caffeine is largely negated by exercise, and it does not lead to dehydration or electrolyte imbalances during prolonged activity.