Creatine Monohydrate: The Most Studied Supplement in History

If you take only one supplement in your life, take creatine. Nothing else in the legal supplement world comes close to its combination of evidence, effect, safety, and price. It has been studied in hundreds of trials over more than thirty years, it works for almost everyone, and a tub costs less than a single restaurant meal and lasts months. My tub is Naked Creatine, which is exactly what you want: pure creatine monohydrate with literally nothing else in it.

Because creatine is so proven, the interesting questions are not "does it work" but "how does it work, what should I ignore, and what should a 38-year-old specifically care about." This guide answers all of that, cuts through the loading and fancy-forms noise, and explains why creatine has quietly become as much a longevity and brain supplement as a gym one.

What Creatine Is

Creatine is a compound your body already makes and stores, primarily in skeletal muscle. Your liver, kidneys, and pancreas synthesize roughly 1-2 grams per day from the amino acids glycine, arginine, and methionine, and you get more from meat and fish in your diet. About 95% of your body's creatine is stored in muscle as phosphocreatine and free creatine.

Here is the key fact: your muscles are not naturally fully saturated with creatine. Most people walk around at roughly 60-80% of their muscles' creatine storage capacity. Supplementation tops off that tank, raising muscle creatine stores by roughly 20-40%. That headroom between your natural level and full saturation is the entire opportunity creatine supplementation exploits.

How It Works: The ATP Engine

To understand creatine you need to understand ATP. Adenosine triphosphate (ATP) is the immediate energy currency of every cell. When a muscle contracts, it spends ATP, converting it to ADP (adenosine diphosphate) and releasing energy. The problem: muscles only store enough ATP for a few seconds of maximal effort. To keep going, you have to regenerate ATP fast.

That is creatine's job. Phosphocreatine donates its phosphate group to ADP to rapidly regenerate ATP, refilling the tank almost instantly during short, intense bursts. The more phosphocreatine you have stored, the faster and longer you can regenerate ATP during those efforts. In practical terms:

• You get a slightly higher ceiling on maximal force output.
• You can perform one or two more reps before the set fails.
• You recover slightly faster between sets, maintaining performance deeper into a workout.

None of those is dramatic in isolation. An extra rep here, slightly better set there. But training adaptation is cumulative. A few more quality reps every session, multiplied across every workout for months and years, is meaningfully more total training volume, and volume is a primary driver of strength and muscle growth. Creatine does not build muscle directly; it lets you do the work that builds muscle. (For the volume side, see the training volume guide.)

The Strength and Muscle Evidence

The performance evidence for creatine is about as strong as sports science gets. The International Society of Sports Nutrition's position stand on creatine, the most authoritative summary available, concludes that creatine monohydrate is the most effective ergogenic nutritional supplement available for increasing high-intensity exercise capacity and lean body mass during training.

The numbers from the broader literature:

• Strength: Creatine supplementation combined with resistance training increases strength gains by roughly 5-15% above training alone, across a wide range of studies and populations.
• Lean mass: Meta-analyses consistently show greater gains in lean body mass with creatine versus placebo, on the order of a couple of extra pounds over a training block, partly intramuscular water and partly genuine muscle protein accrual driven by the extra training capacity.
• Power and high-intensity work: Improvements in repeated sprint performance, jump performance, and total work in the gym are well documented.

Importantly, these effects are real across men and women, younger and older lifters, and trained and untrained individuals. There is a subset of "non-responders", people with already-high muscle creatine (often heavy meat eaters) who have less headroom to fill and therefore see smaller effects, but true non-response is less common than internet lore suggests.

The Water-Weight Myth

The most persistent piece of misinformation about creatine is that it "just makes you hold water" or causes bloating. Let me dismantle this carefully, because it scares people off a great supplement.

Creatine is osmotically active, meaning it draws water with it. When you saturate your muscles with creatine, water follows it into the muscle cells (intracellular), not into the space under your skin (subcutaneous). This is the opposite of the puffy, smooth "bloat" people fear. Intramuscular water makes muscles look fuller and rounder, and there is even a theory (cell volumization) that the swollen, hydrated cell state is itself a mild anabolic signal.

The typical 1-3 pounds of weight gained in the first week or two of creatine is mostly this intramuscular water. It is not fat, and it is not the bad kind of water retention. Once your muscles are saturated, weight stabilizes. The old "bloating" reputation came mainly from aggressive 20g/day loading phases, which can cause some temporary GI water shifts and stomach upset. At a simple 5g/day, the vast majority of people notice no bloating whatsoever, just fuller muscles.

Brain Function and Healthy Aging

This is the part of the creatine story that has exploded in recent years and is the reason I think of creatine differently at 38 than I did at 25. Your brain, like your muscles, runs on ATP and uses the phosphocreatine system to buffer its energy supply. That means creatine is not just a muscle supplement, it is a cellular energy supplement, and the brain is an energy-hungry organ.

The emerging evidence:

• Cognition under stress. Creatine supplementation has been shown to improve aspects of cognitive performance, particularly under conditions of stress such as sleep deprivation or demanding mental tasks. When the brain's energy system is taxed, the extra phosphocreatine buffer appears to help.
• Memory in older adults. A 2023 systematic review found that creatine supplementation improved measures of memory, especially in older adults, where baseline brain creatine may be lower.
• Healthy aging and muscle preservation. Combined with resistance training, creatine helps older adults preserve and build muscle and strength, which is one of the single most important factors for independence, fall prevention, and metabolic health with age.
• Mood research. There is early, promising research on creatine as an adjunct in depression, again tied to its role in brain energy metabolism, though this is not yet settled.

The throughline is that creatine supports cellular energy availability everywhere it is needed, and the benefits extend well beyond the gym into cognition and the preservation of muscle and function as we age. That broadens the case for creatine from "lifters who want to be stronger" to "essentially every adult."

Loading vs. Just Taking 5g

The loading question confuses more people than anything else, so here is the simple truth: loading is optional and mostly unnecessary.

There are two ways to saturate your muscles:

1. Loading protocol: ~20g per day, split into 4 doses of 5g, for 5-7 days, then 3-5g per day to maintain. This saturates your muscles in about a week.
2. No loading: Just 3-5g per day from day one. This reaches the exact same saturation point in about 3-4 weeks.

Both paths arrive at the identical end state. The only thing loading buys you is speed, full saturation in one week instead of three to four. If you have a competition or a specific deadline, load. Otherwise, skip it. Loading offers no long-term advantage, wastes more creatine, and is the phase most associated with the minor GI upset that gives creatine its (undeserved) bloating reputation. I never load. I just take 5g a day and let saturation happen on its own.

Why Monohydrate Beats the Fancy Forms

Walk into any supplement store and you will see creatine HCl, creatine ethyl ester, buffered creatine ("Kre-Alkalyn"), creatine nitrate, and "micronized" creatine, all marketed as superior to plain old monohydrate, usually at a higher price. Here is the honest verdict: creatine monohydrate is the gold standard, and none of the fancy forms have been shown to outperform it.

Monohydrate is the form used in the overwhelming majority of the research, it is the cheapest, and it is fully effective. The alternative forms market themselves on claims of better absorption or less water retention, but the evidence does not support them being more effective, and some are actually less proven or less stable. "Micronized" simply means the powder is ground finer so it mixes more easily, which is a minor convenience, not a different molecule, and is fine to buy (my Naked Creatine is essentially this: pure micronized monohydrate).

Why It's My One Non-Negotiable at 38

The reason creatine's value goes up with age is worth sitting with. Starting around your 30s, you begin a slow loss of muscle mass (sarcopenia) and, eventually, a decline in various aspects of cognitive and cellular energy function. Creatine directly addresses both: it amplifies the muscle-preserving effect of resistance training and it supports the brain's energy buffer. So while a 25-year-old takes creatine for a few extra reps, a 38-year-old (and a 68-year-old even more so) takes it as a foundational tool for staying strong, capable, and sharp. The case strengthens every year, which is exactly why it is non-negotiable for me.

Food Sources of Creatine

You do get creatine from food, exclusively from animal flesh, since creatine is stored in muscle. This is also why vegetarians and vegans tend to have lower baseline muscle creatine and often respond especially well to supplementation.

Notice the practical problem: to get the 5g of creatine a supplement provides, you would need to eat roughly 2-3 pounds of raw beef or fish, and cooking destroys a meaningful fraction of the creatine in the process. That is neither practical nor calorie-efficient as a daily habit. This is the clearest example in the supplement world of "the powder genuinely beats food" for a specific purpose, because the quantities required from food are unrealistic. A flavorless $0.10 scoop of monohydrate does what two pounds of steak would.

Safety, Kidneys, and Side Effects

Creatine monohydrate is one of the safest supplements ever studied. It has been used in trials lasting up to five years, in populations ranging from teenage athletes to elderly adults to clinical patients, with no evidence of harm to the kidneys or liver in healthy people. Major sports nutrition and medical bodies have repeatedly affirmed its safety.

Two points worth clarifying:

• The creatinine confusion. Creatine naturally breaks down into creatinine, which is the same marker doctors measure to estimate kidney function. Supplementing creatine can slightly raise your measured creatinine without any actual change in kidney health, simply because there is more creatine in your system to break down. This can cause a false alarm on a routine blood panel. The fix is simple: tell your doctor you take creatine before any kidney bloodwork so they can interpret the result correctly.
• Pre-existing kidney disease. People with established kidney disease should consult their doctor before supplementing, as a precaution, even though there is no good evidence creatine causes kidney problems in healthy people.

Side effects at 3-5g/day are minimal. The main one is occasional mild GI discomfort, almost always associated with high-dose loading or taking a big dose on an empty stomach. Take it with water and food, skip loading, and even that is rare.

The Bottom Line

Creatine monohydrate is the closest thing the supplement world has to a sure thing. It works through a well-understood mechanism (refilling the phosphocreatine that regenerates ATP), it reliably increases strength, training volume, and lean mass, and it carries decades of safety data. The water it adds goes into your muscles, where you want it. The fancy forms are a waste of money; plain monohydrate is the gold standard. Loading is optional. And the benefits now clearly extend to the brain and to healthy aging, which only strengthens the case as you get older.

For a 38-year-old, creatine is the foundation, the one supplement I would never drop, taken at 5g every single day for muscle, strength, brain energy, and the long defense of the muscle mass that keeps you capable for life. It is cheap, it is safe, and it is proven beyond reasonable dispute. If you are going to be deliberate about exactly one supplement, make it this one.

References

1. Kreider, R.B., et al. (2017). International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 14, 18.
2. Branch, J.D. (2003). Effect of creatine supplementation on body composition and performance: a meta-analysis. International Journal of Sport Nutrition and Exercise Metabolism, 13(2), 198-226.
3. Rawson, E.S., & Volek, J.S. (2003). Effects of creatine supplementation and resistance training on muscle strength and weightlifting performance. Journal of Strength and Conditioning Research, 17(4), 822-831.
4. Avgerinos, K.I., et al. (2018). Effects of creatine supplementation on cognitive function of healthy individuals: a systematic review of randomized controlled trials. Experimental Gerontology, 108, 166-173.
5. Prokopidis, K., et al. (2023). Effects of creatine supplementation on memory in healthy individuals: a systematic review and meta-analysis. Nutrition Reviews, 81(4), 416-427.
6. Candow, D.G., Forbes, S.C., et al. (2021). Creatine supplementation and aging musculoskeletal health. Nutrients, 13(3), 877.