EFS Hydration Drink

$34.99 USD


Isotonic formula that provides everything you need to maximize endurance and performance during exercise. With the ideal carbohydrate sources, industry-leading cramp prevention, and key ingredients that support optimal hydration, EFS refuels working muscles faster than ever before.

✓ Provides immediate & sustained fuel
✓ Industry-leading cramp prevention
✓Contains patented Suntheanine® for mental toughness


The Ideal Carbohydrates

The latest research shows you can almost double the amount of carbohydrates that can be absorbed without GI distress when fueling with Multiple Transportable Carbohydrates (MTC’s) in specific ratios. The key is to consume specific carbohydrates in the right ratios.

EFS was engineered to maximize carbohydrate utilization by delivering a precise combination of MTC's, glucose and sucrose for next-level endurance you’ll notice the first time you use it.

"When you nail your fueling it's pretty remarkable to see that you can actually get stronger as the race unfolds."
Hannah Otto

Leadville 100 Champion (2022)


We know how frustrating it is to have your day wrecked because you’re seized up with debilitating muscle cramps. It’s the number one issue most athletes face. That’s why we engineered EFS.

Unlike most hydration mixes, EFS delivers a clinically effective dose of all 5 electrolytes (sodium, potassium, chloride, calcium, magnesium) in the levels shown to prevent cramping.


“The latest EFS formula is a breakthrough in sports hydration. With more electrolytes than competitors and ingredients to improve mental focus, you’ll finish the race as strong as you started.”

Phil Gaimon (2x World Hillclimb Champion)


We spared no expense upgrading the EFS drink mix, investing in the latest research-driven innovation and technology. The isotonic formula delivers complete nutrition that supports physical and mental performance, redefining the limits of endurance nutrition so you can redefine your limits of endurance.

Pro Tip: For best results have a serving of EFS 30 minutes prior to training and racing.


The brain plays an essential role in endurance and performance. Mental toughness and presence of mind are equally as important as fitness. You have to be able to suffer and handle stress when your body is begging you to stop.

That’s why the reimagined EFS includes Suntheanine ®, a patented innovation that gives you the mental toughness you need to push further and find a gear you didn’t know you had.

Suntheanine® is protected by over 40 U.S. and international patents for its various physiological efficacies and L-isomer specific production processes.



To keep your performance going after two hours of exercise, recent research shows BCAAs taken during exercise – not before or after – keep the flow of fuel sources from carbs and fats mobilized and upsized when you need them the most.The final sprint, the push to the summit, grinding out the last interval - BCAAs are critical when you’re on the limit but there’s still more work to do. In EFS, BCAAs unlock a final emergency fuel source when all other options – and all of your competitors – are exhausted.

"The new EFS drink mix tastes great, helps keep you focused during long and hard training sessions, and fuels the body properly."
Matt Hanson

5x IRONMAN / 5x 70.3 Champion / Holds the record for the fastest full-distance IRONMAN (7:39:25)


Suntheanine® boosts mental toughness to help you push through suffering

Prevents cramping and dehydration—delivers 1160mg of electrolytes

Carbs from multiple sources provide immediate and sustained fuel

7% osmolality ensures bioavailability and reduces GI distress

Citric and malic acids promote oxygen uptake and energy production

New taste profile eliminates the flavor vs function compromise


EFS provides everything you need to maximize endurance and performance. Our industry-leading electrolyte levels help you stay hydrated and avoid cramping.

With the latest amino acid technology and ideal carbohydrate sources, EFS refuels working muscles faster than ever. Plus, the new flavor technology eliminates the formula over flavor compromise.

With EFS, you can train and race with confidence knowing you don’t have to worry about gaps in your nutrition.

"Beyond the importance of Suntheanine, I think the new flavors are the biggest advancement."
Jeffrey Rocco, MD


EFS is for use during exercise to prevent cramps, maintain fuel levels, and support mental toughness when it’s needed most. It can be supplemented with Liquid Shots before and during an event, and Ultragen helps consolidate gains during recovery between sessions. 

Regardless of your training load, a daily dose of our MultiV and Optygen lines help you lay a foundation to achieve your goals.

"On-the-bike taste was great. I felt amazing on the bike today! I had a PR on the top half of the climb. Surprised by this, because I had skied hard the day before."
Doug Davis

Cat I Cyclist


From the carbohydrates (osmotically balanced with your body in a 7% solution) to the electrolytes (20-100% better absorption rates), every ingredient in EFS is selected and portioned for faster and easier absorption without GI distress.

The inclusion of citric and malic acids also encourages oxygen uptake and production of ATP (the body’s energy source), helping your cells use the fuel once it’s delivered.


We prioritize purity by using only Suntheanine, the original and cleanest L-theanine, and free-form amino acids, which have a purity level of 99-100%.

We also omit ingredients with no value—even the ubiquitous vitamin C, which features in virtually every other mix despite research that shows it reduces endurance when taken during exercise. EFS still provides immune system support courtesy of theanine, just without impacting performance.


Our approach to product design eschews unexamined ingredients, traditional processes, and trendy minimalism in favor of research-based innovation, premium ingredient sourcing, and the uncompromising expectations of elite athletes. We’re always ready to show our work and support our products with the scientific literature that informs our design choices, but we also know what virtually every athlete and publication using or reviewing our products learns firsthand: First Endurance products speak for themselves, and you can feel the difference right away.


Supplement Facts
Serving Size: 1 scoop (32 g)
Servings per Container: 30
Amount Per Serving %DV
Calories-110 Calories from fat-0
Total Carbohydrate 26 g 9%
Sugars 16 g **
Calcium (as DiCalcium Malate) 100 mg 8%
Magnesium (DiMagnesium Malate) 150 mg 36%
Chloride (as sodium chloride) 450 mg 20%
Sodium (as sodium chloride) 300 mg 13%
Potassium (as di-potassium phosphate) 160 mg 3%
L-Glutamine 1750 mg *
Branched Chain Amino Acids (L-Leucine, L-Isoleucine, L-Valine) 250 mg *
L-Theanine 50 mg *
*Daily Value Not Established
**Percent Daily Values are based on a 2,000 calorie diet.
Other ingredients: Sucrose, Maltodextrin, Glucose, Citric Acid, Natural Flavor, Stevia Extract.


Q: How is EFS different than EFS-PRO?

 A: Compared to EFS, EFS-PRO has a more premium ingredients list, delivers more carbs and electrolytes, and includes PharmaGABA® for added mental toughness support. Though EFS is itself a step above the competition, EFS-PRO supports the most demanding efforts in the most extreme conditions by providing even more fuel and cramp prevention while doubling down on First Endurance’s revolutionary approach to supporting your brain like it’s a key muscle for endurance athletics. 

Q: Are there other benefits to drinking EFS or EFS-PRO, besides for training and racing?

A: Absolutely. EFS and EFS-PRO can be used to top off electrolytes and help you calm down so you can get a good night’s sleep the night before (or two nights before) an event or race. When you’ve invested an entire season’s prep in peaking for a specific day, the calming effects of EFS or EFS-PRO can help ensure restless nights leading up to that day don’t undercut your form. 

 Q: Do EFS or EFS-PRO have any artificial flavors or colors?

A: No, but it tastes so good you’d be forgiven for thinking we were cheating.

 Q: Do I need to take a full serving of EFS or EFS-PRO to get a benefit? 

A: No. A higher concentration increases calories and electrolytes. While our recommended serving concentration is designed to maximize theanine’s effects in a steady dose, ingesting reduced amounts will still produce a proportionally scaled effect in terms of promoting calm focus. In other words, if you are a smaller person and normally consume a somewhat reduced amount, you will still get the same benefits.

 Q: Do EFS or EFS-PRO have any stimulants in it?

No. In fact, it does the opposite, calming you down and maintaining a cool, collected approach to whatever you’re doing, whether that’s racing, training, or resting up the night before an event.

 Q: Can I use EFS and EFS-PRO with caffeine?

Yes. The calming effects of EFS and EFS-PRO affect you according to the baseline for caffeine consumption that you’ve established through your daily caffeine habit—err, intake. Keep drinking tea or coffee as usual. 

 Q: How much EFS should I use during my training and racing?

 A: Clinical research shows that a 6-8% solution delivering between 45-60g carbohydrates, >1000mg amino acids, 400-600mg sodium and equivalent balance in all electrolytes should be taken every hour during exercise. Athletes should consume one serving for every 30 minutes of intense exercise. Adjustments should be made based on body weight, training state, heat, individual sweat rates and preference. Use one serving for every 30 minutes as a starting point and adjust as necessary from there.  Additional calories and electrolytes can be added with Liquid Shots.

 Q: How should I mix EFS?

SMALL SERVING: Mix 1 scoop with 21-22oz of water

LARGE SERVING: Mix 1 ¼ scoop with 24-26oz of water

BEFORE: Consume 1 bottle 30 minutes before exercise.

DURING: Consume EFS as needed.

TIP: For additional calories and electrolytes, double the concentration or supplement
with Liquid Shot.

Q: Is EFS vegan friendly?
A: Yes.

Q: Is EFS gluten-free?
A: Yes.

Q: What's the glucose:frucose ratio in the formula?

A: The glucose: fructose ratio in the EFS formula is  6:1 Glc:Fru.

Q: Is there any way to get too much Theanine from EFS or EFS-PRO?

A: Only if you macro-dose (200mg or more in a single or repeated shot). Even if theanine is administered in a single macro-dose, the effect is just a too-calm calm that fades as the theanine leaves your body—Nothing serious or harmful. Click here to learn more about dosing and uptake. Since our EFS or EFS-PRO serving is limited to a gradually administered 80g every hour, you won’t hit that dose of theanine, even with continued use as directed. That’s because theanine is water-soluble, it metabolizes fast and doesn’t accumulate . Once ingested, it’s half gone after 60-90 minutes, and it’s gone completely in 24 hours.  

 Q: Does EFS or EFS-PRO help me hydrate better than water?

A: We won’t name them, but there’s a growing list of competitors in the sports hydration game making the claim that their product hydrates better or faster than water alone. This is a so-what claim predicated on evidence that not only doesn’t apply to endurance athletics, but actually hampers performance during long-term endurance events. For their rationale and claims support these companies cite WHO and other medical guidelines for treating serious dehydration in disease and severe exposure conditions, not the sports nutrition guidelines for healthy athletes in endurance competitions. Also important is the need for more fuel, and these drinks fall short in the fuel department. Check out Dr. Bucci’s extended consideration of these claims here.

 Q: I’ve heard that there are benefits to having protein during exercise. Why doesn’t EFS contain protein?

A: EFS contains 2g free form amino acids per serving which is the equivalent in BCAA and glutamine profile to 9g whey protein. Protein naturally contains BCAAs and glutamine.

Clinical evidence supporting the use of BCAAs and glutamine during exercise dates back to 1991. These clinical studies clearly indicate supplementing with as little as 1g free form amino acids improved performance, reduced post-exercise muscle damage, improved muscle glycogen resynthesis, reduced central fatigue and improved rate of perceived exertion. These are the same claims made by the most recent protein study and clearly support a mechanism for improved performance.

In addition to the clinical support, other factors lead to a decision to use these free form amino acids over complete proteins.

Proteins are more difficult to digest than amino acids during exerciseProteins don’t taste very good during exerciseProteins can reduce the glycemic index of a drink, further reducing its ability to be quickly absorbedThere is considerably more evidence supporting free form amino acids than complete protein

 Q: Are EFS and EFS-PRO safe for kids?

Yes. Just make sure they pay it back during their turns at the front. 

 Q: I am prone to cramping during longer training and racing. Will EFS help me with cramping problems?

A: Nutritionally, cramping stems from electrolyte imbalance, electrolyte depletion and/or dehydration. EFS provides the most potent electrolyte profile available. The combination of all five electrolytes delivers a potent 1160mg per serving, helping to prevent cramping. The 300mg sodium per serving also aids in maximum fluid absorption so you stay hydrated throughout your training and racing. Supplementing with additional salt tabs, electrolyte tabs, or salty snacks is no longer needed when using EFS.

 Q: How should I use EFS/EFS-PRO for races or training that lasts more than three hours?

A: New research suggests athletes can ingest more and more carbs per hour. For detailed information, check out this blog.