The Science

Four hours of focus. Built from research, not hype.

Every ingredient in GC18 was chosen because it has been studied in humans for attention, mental stamina or calm under pressure. This page walks you through that research: the good, the promising, and the honest caveats.

Clinically studied ingredients·Formulated in Scotland

The problem

The back nine

Golf is unusual because it asks for physical energy and precise thinking for roughly four hours. You need enough energy to walk the course and stay switched on, but not so much that you feel wired, jittery or unable to settle over the ball. The ideal state is calm, composed energy.

As the round moves into its second and third hour, mental sharpness can begin to fade. Around the 13th hole, that can show up as a rushed putt, a poor decision or a shortened pre-shot routine. A sharp early caffeine spike followed by a dip can make those moments feel even harder to manage.

GC18 was designed specifically for the demands of golf: sustained energy for the full round, paired with ingredients chosen to support focus and composure. The aim is steady, calm energy without the hard spike, jitters or late-round crash associated with a typical energy drink.

~4 hours

The length of a round, and the window GC18 was designed for.

Customer survey

What golfers told us

Results from our GC18 customer survey, conducted in April 2026.

of golfers surveyed said GC18 improved their game

reported feeling calmer and more relaxed on the course

reported feeling more energised and focused on the back nine

Self-reported results from a customer survey of GC18 users. Not a clinical trial. Individual experiences vary.

The formula

At a glance

Cognizin® Citicoline

Attention and mental energy

50+ years of research

L-Theanine

Calm, steady focus

25+ years of research

Natural Caffeine

Alertness and reaction time

100+ years of research

Rhodiola rosea

Mental stamina under pressure

60+ years of modern research, centuries of traditional use

Cordyceps

Endurance support

Decades of research, centuries of traditional use

Cognizin® Citicoline

Attention and mental energy.

What it is

A naturally occurring compound found in every cell, which the body uses to build brain cell membranes and produce acetylcholine, a neurotransmitter involved in attention and memory. Cognizin® is the branded, clinically studied form.

What the research shows

Originally developed in Japan in the 1970s, citicoline has been studied for over 50 years. Randomised, double-blind, placebo-controlled trials in healthy adults have looked specifically at attention.

McGlade et al. (2012) gave 250-500mg/day to 60 healthy women for 28 days and measured attention on a continuous performance test; the citicoline groups made fewer attention errors than placebo¹.

McGlade et al. (2019) repeated this in 75 healthy adolescent males and reported improved attention and psychomotor speed².

Bruce et al. (2014) tested a drink combining citicoline with caffeine in 60 healthy adults and found faster reaction times, fewer errors on a go/no-go task, and EEG markers associated with sustained attention³. A 2025 trial of 148 healthy adults reported improvements in sustained attention, reaction time and processing speed after 12 weeks at 500mg/day⁴.

Why it's in GC18

Golf is a game of sustained attention with long gaps between shots. Citicoline is the ingredient in the formula most directly studied for exactly that. GC18 contains 500mg per serving.

Key study

Study: Bruce et al. 2014
Design: Randomised, double-blind, placebo-controlled
Participants: 60 healthy adults
Intervention: Citicoline + caffeine beverage vs placebo
Measured: Reaction time, go/no-go errors, EEG
Result: Faster reactions, fewer errors, increased sustained-attention markers

Honest note: Most citicoline attention studies used daily dosing over several weeks. Acute single-dose research in healthy adults is more limited.

L-Theanine

Calm, steady focus.

What it is

An amino acid found almost exclusively in tea leaves, first isolated in Japan in 1949. It's the reason a cup of tea feels alert but calm, rather than wired. GC18 contains 255mg per serving.

What the research shows

L-theanine has been studied in humans for around 25 years. EEG studies (Nobre et al. 2008) show it increases alpha brain-wave activity, a state associated with relaxed alertness rather than drowsiness⁵.

Higashiyama et al. (2011) found 200mg improved attention and reaction time on demanding tasks⁶.

Studies in stressed adults (Kimura 2007) found it dampened the heart-rate and blood-pressure response to stress and reduced self-reported tension⁷.

Why it's in GC18

It's the calm half of the formula. Standing over a four-foot putt, you want alert, not amped.

Key study

Study: Nobre, Rao & Owen 2008
Design: EEG study
Participants: Healthy adults
Intervention: 50mg L-theanine vs placebo
Measured: Brain-wave activity
Result: Increased alpha activity consistent with relaxed alertness

Honest note: Effects are subtle and task-specific; L-theanine is best understood as a modulator, especially alongside caffeine (see below).

Natural Caffeine

Alertness and reaction time.

What it is

The most studied performance compound in the world. GC18 uses 102mg of natural caffeine, roughly [equivalent, e.g. "one strong cup of coffee"], deliberately moderate.

What the research shows

Caffeine is one of very few ingredients with authorised health claims in the UK and EU for contributing to alertness and concentration.

Crucially, it has been studied in golf specifically. Stevenson et al. (2009) gave 20 golfers a caffeine-and-carbohydrate drink across a round; putting performance and alertness held up better over the final six holes compared with placebo¹⁴.

Mumford et al. (2016) gave 12 skilled golfers a moderate caffeine dose (around 155mg) and recorded better total scores, more greens in regulation and longer drives, alongside reduced fatigue¹⁵.

Why it's in GC18

It's the only ingredient with direct golf evidence, and it's dosed to work with L-theanine rather than overpower it.

Key study

Study: Mumford et al. 2016
Design: Randomised, double-blind, placebo-controlled
Participants: 12 skilled golfers (handicap 3-10)
Intervention: ~155mg caffeine vs placebo
Measured: Score, greens in regulation, drive distance, fatigue
Result: Lower scores, more GIR, longer drives, less fatigue

Honest note: These studies tested caffeine on its own, not the GC18 formula.

Rhodiola rosea

Mental stamina under pressure.

What it is

A hardy alpine root used for centuries in Scandinavian and Russian traditional medicine for fatigue and endurance, and studied intensively by Soviet researchers as an "adaptogen" from the 1940s onward. GC18 contains 400mg per serving.

What the research shows

Over 180 pharmacological and clinical studies have been published since 1960. The human trials most relevant to focus looked at mental fatigue in people under pressure.

Darbinyan et al. (2000) studied 56 physicians on night duty and found a standardised extract improved a composite measure of mental performance (memory, concentration, calculation) by around 20% versus placebo¹⁶.

Shevtsov et al. (2003) gave a single dose to 161 military cadets and found improved capacity for mental work compared with placebo¹⁷. Olsson et al. (2009) found reduced stress-related fatigue and improved attention after 28 days¹⁸.

Why it's in GC18

The back nine is where mental fatigue bites. Rhodiola is the ingredient in the formula most studied for holding mental performance steady when you're tired.

Key study

Study: Shevtsov et al. 2003
Design: Randomised, double-blind, placebo-controlled
Participants: 161 military cadets
Intervention: Single dose of standardised extract vs placebo
Measured: Mental work capacity under fatigue
Result: Significantly improved anti-fatigue index in both dose groups

Honest note: Systematic reviews have described the Rhodiola evidence as promising but methodologically uneven, and have called for more independent trials¹⁹. We include it for its long history and consistent direction of findings, not as the headline act.

Cordyceps

Endurance support.

What it is

A fungus prized in Traditional Chinese and Tibetan medicine for centuries as a tonic for stamina and vitality. Modern research took off after Chinese distance runners credited it in the 1990s. GC18 contains 250mg per serving.

What the research shows

Human trials have focused on physical endurance. Hirsch et al. (2017) gave 28 adults a Cordyceps militaris blend for three weeks and recorded improved VO2max and time to exhaustion²⁰.

Earlier work with the Cs-4 strain in older adults showed improvements in aerobic capacity²¹.

A small 2025 trial found a single dose was associated with faster reaction time on a Stroop test after exercise.

Why it's in GC18

Golf is a four-hour walk carrying a bag. Cordyceps is the ingredient chosen for the physical side of stamina.

Key study

Study: Hirsch et al. 2017
Design: Randomised, double-blind, placebo-controlled
Participants: 28 adults
Intervention: Cordyceps militaris blend vs placebo, 3 weeks
Measured: VO2max, time to exhaustion
Result: Both improved versus placebo

Honest note: Human research on Cordyceps and cognition specifically is still early. Most of the mental-fatigue evidence comes from laboratory studies, not human trials. We're upfront about that.

The pairing

Why GC18 doesn't feel like an energy drink

L-theanine and caffeine together is one of the most studied nootropic pairings in existence, with over a dozen randomised controlled trials, plus a 2014 systematic review and meta-analysis.

Haskell et al. (2008) found the combination improved reaction time and accuracy while reducing tiredness and headache⁸. Owen et al. (2008) found improved speed and accuracy on attention-switching tasks and reduced susceptibility to distraction at 60 and 90 minutes⁹.

Giesbrecht et al. (2010) found improved task-switching accuracy and alertness¹⁰. Camfield et al. (2014) pooled 11 trials and found moderate effects in favour of the combination on alertness and attention-switching in the first two hours¹¹.

There is also a "smoothing" effect. Rogers et al. (2008)¹² and Dodd et al. (2015)¹³ found L-theanine attenuated caffeine's rise in blood pressure, the physiological basis for a steadier, less jittery kind of alertness.

Honest note: One study (Rogers 2008) found L-theanine did not change how jittery people said they felt, even though it reduced the blood-pressure response. The evidence is stronger for the physiology than the feeling.

Caffeine alone: spike, then dip Caffeine + L-theanine: smoother curve

Illustration of the concept only. Not data from a study.

Timing

Why four hours

A conventional coffee or energy drink can feel front-loaded: an early lift followed by a noticeable dip around the middle of the round. GC18 combines a moderate caffeine dose with L-theanine and the rest of the formula to support a calmer, steadier experience across the demands of 18 holes.

We recommend taking GC18 15 minutes before the first tee, or when you feel you need it most. If that is at the ninth, take it then.

First tee

Take GC18 15 min before, if this is when you need it

Front nine

Calm energy settles into the round

The turn

Take GC18 here if this is when you need it most

Back nine

The window GC18 was designed for

18th

Finish the round, not the crash

Honest note: The four-hour window is based on how these ingredients behave in the body; GC18 itself has not yet been tested in a clinical trial. Our customer survey is the first step, and a controlled study is planned.

Our commitment to evidence

We only use ingredients with published human research.
We tell you where the evidence is strong and where it's still developing.
We are planning an independent study of GC18 itself. We'll publish the results whatever they show.

Sources

References

1.McGlade E et al. Improved attentional performance following citicoline administration in healthy adult women. Food and Nutrition Sciences. 2012.
2.McGlade E et al. The effect of citicoline supplementation on motor speed and attention in adolescent males. Journal of Attention Disorders. 2019.
3.Bruce SE et al. Improvements in concentration, working memory and sustained attention following consumption of a natural citicoline-caffeine beverage. International Journal of Food Sciences and Nutrition. 2014.
4.Nakazaki E et al. Citicoline and memory function in healthy older adults. Journal of Nutrition. 2021.
5.Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pacific Journal of Clinical Nutrition. 2008.
6.Higashiyama A et al. Effects of L-theanine on attention and reaction time response. Journal of Functional Foods. 2011.
7.Kimura K et al. L-Theanine reduces psychological and physiological stress responses. Biological Psychology. 2007.
8.Haskell CF et al. The effects of L-theanine, caffeine and their combination on cognition and mood. Biological Psychology. 2008. PMID 18681988.
9.Owen GN et al. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutritional Neuroscience. 2008.
10.Giesbrecht T et al. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutritional Neuroscience. 2010. PMID 21040626.
11.Camfield DA et al. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutrition Reviews. 2014.
12.Rogers PJ et al. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology. 2008.
13.Dodd FL et al. A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology. 2015.
14.Stevenson EJ et al. Effect of a carbohydrate and caffeine drink on golf performance. Applied Physiology, Nutrition, and Metabolism. 2009.
15.Mumford PW et al. Effect of caffeine on golf performance and fatigue during a competitive tournament. Medicine & Science in Sports & Exercise. 2016.
16.Darbinyan V et al. Rhodiola rosea in stress induced fatigue: a double blind cross-over study of a standardized extract SHR-5 on the mental performance of healthy physicians during night duty. Phytomedicine. 2000.
17.Shevtsov VA et al. A randomized trial of two different doses of a SHR-5 Rhodiola rosea extract versus placebo and control of capacity for mental work. Phytomedicine. 2003. PMID 12725561.
18.Olsson EM et al. A randomised, double-blind, placebo-controlled, parallel-group study of the standardised extract SHR-5 of Rhodiola rosea in the treatment of subjects with stress-related fatigue. Planta Medica. 2009.
19.Hung SK, Perry R, Ernst E. The effectiveness and efficacy of Rhodiola rosea L.: a systematic review of randomized clinical trials. Phytomedicine. 2011.
20.Hirsch KR et al. Cordyceps militaris improves tolerance to high-intensity exercise after acute and chronic supplementation. Journal of Dietary Supplements. 2017. PMID 28094746.
21.Chen S et al. Effect of Cs-4 (Cordyceps sinensis) on exercise performance in healthy older subjects. Journal of Alternative and Complementary Medicine. 2010.

GC18 is a food supplement. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Contains caffeine (102mg per 60ml serving); not recommended for children or pregnant or breastfeeding women. The research described on this page relates to individual ingredients and has not been conducted on GC18 itself. Customer survey results are self-reported and are not a clinical trial.